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Help on a divide and blend circuit - wet and dry - tl072

Hello,i want to build a "divide and blend" circuit with one potentiometer to blend between a dry and wet signal, the source will only be audio and the wet signal will be a clone of the MS-20 filter.my knowledge of electronic is almost zero... so i looked on different circuits and tried to adapt to what i want, but i need you guys to confirm if what i've designed works? do you see any problem? to you have any suggestions? thank you very much

Question by FilipeB21    |  last reply


Infinity divided by 0?

Does infinity divided by zero theoretically equal any number other than 0 or infinity? I heard something about ohm's law applied to a circuit with an ideal voltage source (which is only theoretically possible) and having the terminals shorted out and at 0 ohms, resulting in the current going up to infinity? 

Question by .Unknown.    |  last reply


Transformer vs Potential divider

Hi guys! I got bored and decided to make a study table light using LED's. My setup consists of 4 LED's in an arm and 10 such arms in parallel. I actually designed it in view that the transformer i used converts 230v - 15v. But after it all finished, i found out that all my transformers are used up for other circuits. I was wondering,  Can i use a potential divider for such simple circuits? I approximated that if i place a 46K and a 3K resistor in series and take the voltage across the 3k resistor, i will have about 15 v. What are the disadvantages of using such potential divider? 

Topic by charmquark    |  last reply


Hows this circuit as mileage meter? Answered

I recently got permission from my parents to hack the car,so I thought,what mod is most suitable in India.so I came up with an idea of milage meter My dad told me that the amount of petrol used in each cycle of engine is the same,adjusted to optimum level. So I thought that if i can divide the rpm value with speed,i'll get rounds per distance,ie fuel consumption per distance. and i devised the following circuit for it-

Question by Suraj Grewal    |  last reply


Why can't I use a voltage divider?

I am working on building my own firework controller. the whole thing will be powered by 6v dc, with the exception of the test circuit this going to run on 1.5v (I am using an optocoupler to separate it from the 6v). I was just going to use 2 resistors to make a voltage divdered to get the volatge down to 1.5. I just read however that "voltage dividers should not be used to supply power to a load". My question is why cant I use this method? When do you actually use this method? and what should I use to properly reduce the voltage? 

Question by Mpc1055    |  last reply


analog circuit to mimic constant resistance load? Answered

I unfortunately do not have many big resistors that can dissipate lots of power, and would like to make a dummy load to test and parameterize batteries and power supplies. I want constant power, constant current, and constant resistance load, I do have lots of opamps and a few N and P channel enhancement mode MOSFETs as well as many 2N3055s and a couple MJE2955's. I think constant current is the easiest, since all I need to do is make a closed loop controller that will turn off the transistor as the current is exceeded, and turn it on as the current falls. Constant power might be more tricky, as I need a device that controls the bias on a transistor as a function of the product of the voltage and current, since P=IE or W=AV, and similarly, constant resistance, I need a thing that will divide voltage across the pass element by the current through it. I don't want to use a "slow" microcontroller for this, I like nice continuous analog control system, if that is possible.

Question by -max-    |  last reply


40kHz Ultrasonic Receiver Wanted

I'm looking for a breakout board, module, etc that is basically a 40kHz ultrasonic receiver, where if it detect a 40kHz signal it puts a pin high sort of thing (volume level as a PWM whatever, I just need to know when there is a 40kHz signal near by). I was thinking of using a HC-SR04 Ultrasonic Range Finder but they only receive for a very short time after the trigger pin goes high, I need it to constantly be sensing.Ideally works with a Raspberry Pi (ie 3.3 volts output, but 5v just means I add a voltage divider not a biggie)Thanks

Question by Duke Nukem  


Do LED's need to be mounted to a circuit board, or can they be attached in some way to a tube of some sort?

Most LED circuits, like DIY brake lights are mounted to a board & covered w/ a plastic lens cover like a typical brakelight. My plan is to leave it exposed, if possible so that it sort of blends in until it is actually illuminated.

Question by gamnoparts    |  last reply


How can I reduce the output voltage of a zener diode?

Hello, My main goal here is to get an LED to light up when it "detects" over 30V, regardless of the specific output of the voltage source. I attached here an image of the circuit that I currently have. The output of the zener diode is about 30V. What I want to do now is reduce this output to 2V in order to light up an LED that has a 1.8-2.2 VDC forward drop and a max current of 20mA.  I was thinking of attaching a voltage divider to this circuit in order to lower the 30V to 2V, but I'm not sure how, especially with the zener diode involved. Can anyone help me?

Question by frossiove    |  last reply


PCB Repair Process of 3 different kind of circuits

1 Power Supply Circuit: During the circuit board repair process, power supply part should be inspected at the first hand and then come to the other part. +/-5V, Power supply failure can occur under below several situation: (1) NO power supply voltage or power supply voltage is deficiency, NC system is often used +/-5V, +/-12V, +/-15V and +/-24V, a few of them use +3.3V, and the varied or unstable voltage of power supply will cause the system working impropery; (2) Use voltmeter to test the voltage of power supply, and the result show is normal. Voltage waveform detected by oscillograph has shown the existence of big ripple. This situation maybe caused by open circuit of Filtering capacitance, bad rectifier diode or cold soldering, but sometimes it could be caused by an overloaded component which has been brokendown and damaged by power. (3) System can run properly when it is just being opened, after a while of operating, the voltage begin to drop off. This is usually caused by voltage stabilizing circuit and large power triode. (4) The voltage decrease accompany with temperature increase maybe cause by component cold soldering, it is electrical connection can be affected negatively when the temperature high up. (5) NO power supply voltage or supply voltage decreases significantly will cause the system to interrupt or stop working, this fault can be detected and spotted easier. (6) When the capacity of power supply load drop off or filter circuit become invalid, it will cause the system halt suddenly, this situation which is very difficult to justify can bring damage to the equipment and facility even get personnel wound. 2 Clock Circuit: Clock circuit mainly exist on the systematic motherboard, it is the foundation of large-scale integrated circuit system through which it can work, it can generate the constant square signal in the circuit base upon the crystal oscillator (commonly known as crystal), Once the crystal oscillator stop working, it is same as the heart of human being stop beating, the whole system will fall into the status of paralyzed, only after crystal can work under normal condition, the systematic circuit can operate under the command of CPU according to the frequency of crystal. The number and frequency of the crystal could be different due to the variety of numerical control system, but generally will at least one crystal, different clock frequencies required by the other circuit can be solved by frequency dividing circuit or other crystal. Crystal possess a higher rate of failure or damage, below are some malfuntions of crystal: (1) Leakage: Use multimeter and switch to P*10K level to test it, if the resistance is infinite, then it can be viewed as normal; (2) Internal OPEN CIRCUIT: Value of resistance is infinite tested by Use multimeter, can fail to generate oscillating pulse in the circuit; (3) Alternative crystal: Due to the transformation of crytal will cause its internal parameter change which can only be detected by osillagraph or cymometer. Although the crystal can still has oscillation, but the clock frequency is deviated from its nominal value, and the still existing oscillation pulse can’t make system circuit work properly due to the value of oscillation is wrong. Only cymometer can test its tolerance now. (4) In clock circuit, the both ends of crystal would be connected to ground by one ceramic capacitor value range from several picofarads to tens picofarads, failure of the clock circuit result from this capacitor leakage, deterioration is also more common. The best tool to test whether the crystal is good or bad could be oscillagraph or cymometer, multimeter is very difficult to detect the root cause. 3 Reset Circuit Reset circuit also exist in the circuit system of motherboard, it is unique set of large-scale digital integrated circuit. Microprocessor and interface circuit are all possess reset terminal. Reset pulse generate by reset circuit will clear the progam counter, force CPU recall the orginal files from the memory, execute initiation process on all the controller chips, system will occurs the phenomenon of disorder or crash as a result of faulty reset circuit, the method of using cymometer to illustrate the reset pulse is turn on/off power supply repeatly, observe and record the pulse value at the right moment of power supply on/off since it should be the normal square wave-form. If there is no existence of reset pulse, all the resistor, capacitor and transistor in the reset circuit should be detected. The reset terminal of integrated circuit should be regular low or high electrical level, or else, it is probably the malfunctional reset circuit or damaged integrated circuit.http://www.circuit-engineering.com

Topic by circuiteng    |  last reply


more output current with LM317 ?

Hi, for some time I have been wondering if I can make LM317 to output more than 1.5Amps. After many hours of searching I found that I can achieve this in 2 ways. The circuits are in LM317 datasheet which can be downloaded from here : http://www.ti.com/lit/ds/symlink/lm317.pdf 1- By using a transistor with LM317 (page 16) . 2-By using several LM317 regulators in parallel and using TL080 (page 15). Second one seems better IF load is equally divided between regulators, it also has the benefit of producing less heat when  high currents are drawn. My question is: will the second circuit (LM317s in parallel) work and output more than 2Amps? is load equally divided between regulators in this design ? can I replace TL080 with another IC ? By the way, there is a circuit in page 12 called "tracking preregulator" , what is the purpose of this design ? PS. I know there are switching regulators which output more current, but I'd like to experiment with LM317.

Question by ehsan_zt    |  last reply


96 by 286 LED Light strobe.

Hi I am Michael, and i want to make a Name board which will have 2 parts. it will have 382 in total divided in 2 parts leds96/286.  I want to make a strobe controller for these many leds.  it should blink 96 led at one time and the other 286 at other time. Please help with the circuit diagram or the schematics Thanks. michaelferns1@gmail.com

Question by michaelferns1    |  last reply


74hc193 equivalent? Answered

Dear All. I have an schema circuit 74193 divider frequency to N (2 to 15) without using  other component .But my regional haven't sale 74193 . So please help me to known  what the chip CD4520 - CD4510- CD4029- CD40193  or other IC  can instead of 74193 (TTL  or CMOS don't matter). Thank you in advance for your time.                                                    Best regards

Question by lam.huuminh.3    |  last reply


Dropping 1v?

I'm designing a circuit for a very high precision installation, and I need to regulate a 6VDC supply to 5VDC. I have looked at various regulators, but most seem to require at least 2v above the output. It also needs to be very precise, available in a 500mA package, and have a very low current draw. The less external components required, the better. Voltage dividers won't work as the battery will vary in voltage from full to empty.

Question by andy70707  


read external 6V power source via 5V driven arduino?

I need to check external 6V voltage for a servo circuit on my 5V USB driven arduino uno - in order to not waste power & "over-power" the arduino's analog pin reading the external 6Vt: - should i use a voltage divider with high resistor values? i look forward to your advice …

Question by marc_is_curious    |  last reply


Autorange Brymen BM511?

I have an unusual problem. My BM511 will not auto-range and readings on VDC are odd. A 1.5v battery initially shows OL, then 00.61, 001.5 then 0002V as you manually step up through the range of the meter using the 'range' button. I suspect it has been burnt, either the input protection, bridge or scale divider. As I do not have a diagram i cannot fault find. Does anyone have a circuit diagram for the Brymen BM511 DMM. Thanks in advance. Regards, KH

Question by KeithH65    |  last reply


LED 3 Watt Testing

I recently purchased 13- 3 watt LED's.  I'm trying to establish a high out put LED light.  I also purchased a LED Driver Transformer 48 Watt 120 Volt to 12v DC 4 Amp. First I would like to test each LED using the same divider.  I'm thinking that if I create a voltage divider two 330 ohms to limit the current and reduce the voltage to about 6 volts that would allow me to test with the driver that I purchased.  Secondly, will this driver be enough to drive all my LED's and would I have to reduce the voltage down too since it appears to push out enough wattage and amperage for the total number LED's I'm putting together?   I'm building my circuit based on this video. http://www.youtube.com/watch?v=4qYZahe2s5o&NR;=1   Assistance would be greatly appreciated.  Regards,

Topic by lancruz    |  last reply


using 1 watt LEDs with a 4017

I want to build a chaser type light array using a 4017 counter divider circuit, 555 timer and the ever popular 1 watt luxeon LEDs, but I don't think that the 4017, or the 555 can withstand the current that will be going through them. I know in most cases you can simply toss a heatsink on the component and it will be fine, but I don't know if this will work with the ICs. https://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId;=10001&catalogId;=10001&productId;=12749Here is the spec sheet for the 4017. Thanks

Topic by John Culbertson    |  last reply


Solar charging a battery with Arduino?

I am making a solar rover robot using an arduino duemilanove. I have a 12 volt solar panel and a 9.6 volt nicad battery. I am wondering if this circuit I sketched http://www.flickr.com/photos/56541142@N02/5229716662/ would allow me to prevent the battery from over charging. The battery is monitored by dividing the voltage and connecting it to analogue input on the arduino. When the battery is fully charged, the arduino sets an output pin HIGH and breaks the connection between the panel and the battery using a PNP transistor. Does the transistor subtract current from the circuit? In the open state will there be more than 9.6 volts entering the battery? here are some links to the robot so far! (without solar installed) Pics! http:// http://www.flickr.com/photos/56541142@N02/with/5229716662/ Video! http://www.youtube.com/watch?v=YZkXnul2j5M

Question by Revolt Lab  


+Help with Digital PSU+?

Hi everyone after many days of constant tinkering, I finally got the circuit of my Digital Power supply made. However, I am experienced difficulty in the programming side. I am using an Arduino with an LCD (and various other io such as a current sensor, voltage divider, button and rotary encoder). My program is limited to what I could find online for an ammeter/ voltmeter sketch. I wanted help or some guidance in figuring out how to use the rotary encoder to 'set' a voltage (visible on the lcd) and when i press the button, i send a certain signal to my DAC which is connected to my psu circuit. and i wanted to be able to switch over from voltage 'setting' to current 'setting'. Frankly, i have no idea how to do this :s ! here is a video of what i want it to almost look like https://www.youtube.com/watch?v=bGnTzT_OCpc Thanks  

Question by making9719    |  last reply


Help with LM741 op-amp? Answered

Just to test it out, I hooked up a voltage follower with a LM741 Op-amp. But, when I measure the voltages, it doesn't work. When I have problems with such simple circuits, it makes me want to kick a small animal. Please, save the small animals, help me with my circuit. When I measure Vout, I expected something somewhere around 7-8 volts, but I'm actually getting 13-14 volts. I also tried changing the resistors in the voltage divider, but the output did not change. I'm getting my power from an unregulated 12v 1A wall transformer, but I measured it at around 15v unloaded. I replaced the chip once to rule out static electricity as the problem, and I got an output 0.1 volt higher. Any ideas?

Question by WerdnaN    |  last reply


Please help me Open Source Air Particle Counter

Please help me I'm making this project:https://www.instructables.com/id/How-to-Build-a-Po...the part of the circuit is already ready, I have difficulty understanding the program (you can also explain it to me with a flowchart or simply in words)- I did not understand the software how it counts and divides the particle size?-pin c6 (mosi) what function does it perform? - the frequency of the clok and when it is givenfrom luigi from italy

Question by luiiii  


Testing a 3 watt LED? Answered

I recently purchased 13- 3 watt LED's. I'm trying to establish a high out-put LED light. I also purchased a LED Driver Transformer 48 Watt 120 Volt to 12v DC 4 Amp. First I would like to test each LED using the same divider. I'm thinking that if I create a voltage divider two 330 ohms to limit the current and reduce the voltage to about 6 volts that would allow me to test with the driver that I purchased. Secondly, will this driver be enough to drive all my LED's and would I have to reduce the voltage down too since it appears to push out enough wattage and amperage for the total number LED's I'm putting together? I'm building my circuit based on this video. http://www.youtube.com/watch?v=4qYZahe2s5o&NR;=1 Link to website data of 3 Watt LED. http://ledsupply.com/indusstar-1up.php Assistance would be greatly appreciated. Regards, 

Question by lancruz    |  last reply


Testing 3 Watt LED's

I recently purchased 13- 3 watt LED's. I'm trying to establish a high out-put LED light. I also purchased a LED Driver Transformer 48 Watt 120 Volt to 12v DC 4 Amp. First I would like to test each LED using the same divider. I'm thinking that if I create a voltage divider two 330 ohms to limit the current and reduce the voltage to about 6 volts that would allow me to test with the driver that I purchased. Secondly, will this driver be enough to drive all my LED's and would I have to reduce the voltage down too since it appears to push out enough wattage and amperage for the total number LED's I'm putting together? I'm building my circuit based on this video. http://www.youtube.com/watch?v=4qYZahe2s5o&NR;=1 Link to website data of 3 Watt LED. http://ledsupply.com/indusstar-1up.php Assistance would be greatly appreciated. Regards, 

Topic by lancruz    |  last reply


HC06 Bluetooth module, can't find it when I search for it

I paired to my HC06 Bluetooth module from my android phone then used application to drive my RC car without any issue. After that I tried to connect from the laptop or even from the same phone but I couldn't find it when I search for it, Although I'm still able to connect through the APPLICATION only and control my RC car.I have other HC06 bluetooth module which I couldn't find it at all when I search for it. so is that a normal problem with the HC06 and is there any solution for it ? or it is just a problem in my installation.NOTE: I used a voltage divider circuit from the Arduino Tx pin to the module Rx pin, there is a red led on the module flashing slowly when I turn the circuit On.

Question by omaralani28889  


Where have all the EE's gone; long time passing......

I'm trying to upgrade the control circuit on my cheap TIG welder. The existing control is a 10k ohm potentiometer, mounted on the welder. It's wired up such that the voltage drop across the pot is proportional to the welders output. Instead of having one knob that controls the output, I want one knob on the welder's panel that selects the maximum output, and another knob ( to be mounted in a foot pedal control) that allows me to select output power from zero up to the maximum value that is set on the panel knob. Seems to me that there should be a relatively simple, elegant solution that gets covered in the second year of an electrical engineering course. Or am I just insane to think that such a thing should be simple? I've tapped out my own social network, and I can't find anyone who will admit to being an electrical engineer. Thanks.

Topic by CTroyer    |  last reply


I want to make an RGB LED microlight that has multiple modes for which it flashes with PWM. rainbow fade, slow/fastblink

Http://www.youtube.com/watch?v=Sqq0doh7Dto I want to make my own version of this. I'm willing to do whatever it takes. Can someone point me in the right direction? Its has to be a small portable flashlight and run off of small batteries. It has to have multiple modes: one of which is a rainbow fade, another of which is a super fast blinking mode). I understand Pulse Width Modulation achieves this, but I've only seen LARGE circuits that achieve this in comparison with the size of a microlight. I don't think a 555 timer circuit would work for me since it would be too large and I would need 3 to controller the RGB. I understand that microcontrollers are needed to control the modes, what type of microcontroller could i use that is that small? If filmed under time lapse, I want to achieve the effect in the picture for a mode: http://lightzombies.com/store/images/Blending%20Rainbow%20-%20White%20Blue%20Green%20(1).JPG Any help is very very welcome. This is an extremely important project to me.

Question by SpiffyChee  


usb to fm transmitter

 Hi, I am a very big noob to wiring. For a present, I wanted to make my cheap old AAA powered fm transmitter into a usb powered one.  Thinking I was so smart, I cut up an old usb cord and soldered the red to positive and black to negative. It worked great until it started melting the transmitter.  So I now I realize that usb is much more powerful than 2 AAAs.  heh heh. I found this: www.instructables.com/community/USB-to-Travel-Clock-Circuit-Help-/ but it's a bit over my head.  I'm assuming I need to get a capacitor or voltage divider but I could use a little help breaking it down into noob speak.  Plus the transmitter is a little thing, 2 inches, is there a smaller way of checking the voltage? K, thanks bye!

Topic by audrywolters    |  last reply


Having trouble measuring accurate voltage with arduino.

For a week now I’m trying to get very precise voltage readings with no luck so far. I’m using a voltage shunt regulator (LM431) for reference but still. My goal is to read values low as a 1mv change. I’m using a voltage divider to convert 38 volts to 4v (According to my vref). I've read that 10 bit ADC in atmega328 is enough for this job. Is it or am I doing something wrong? Thanks P.S i have made a lot on changes to my circuit so please go over to my new link to get up to date. Ive read all of your feedback and tried to implement it. Thanks a lot for all your answers.  LINK: https://www.instructables.com/answers/Having-trouble-measuring-voltage-with-arduino/

Question by faraz ahmed khan    |  last reply


How to convert 300 volts DC to 30 volts DC?

Alright so i made a simple full bridge rectifier (http://www.electroboom.com/?p=544) credits to Medhi Sadahagar. I modified it such that it works with 240 volts mains instead of 120 volts mains. my capacitor bank is 2.4 mF and 400 volts. However, the output is 312 volts DC and I require around 12-36 volts DC at minimum 10 amps to power a ZVS driver (by Plasmana). I tried a voltage divider but I think the power rating of my resistors was not enough as one of them heated up and broke. I need help in designing or making a suitable circuit to reduce 312 volts DC to 12-36 volts DC at 10 amps minimum. Please help me and have a great day :D 

Question by BenderSanchez    |  last reply


Troubleshooting unwanted distortion in a DIY guitar effect pedal? Answered

I built myself one of Moosapotamus' Bass Paraloopers following his design (the updated one, that is) to the letter.  The only modification I did was to remove the low pass filter, since I'm using it for guitar, not bass.  Unfortunately, it has several problems. The one I am most concerned about is some unwanted distortion.  It is fairly mild, but noticeable enough to be a problem when playing clean.  It affects both the dry and wet signal (i.e. it is present when the blend knob is set to both 100% wet and 100% dry).  I do not think the signal from the effects pedal in the loop is overdriving the circuit.  How can I narrow down where/what component this distortion is coming from?  Unfortunately, I do not have an oscilloscope to use for troubleshooting.  Any help is appreciated.

Question by RelaxedSoup    |  last reply


Odd Breadboard Question

Hi All  I am brand new to hobby electronics and would love one day to be able to create the endless amount of cool Instructables but I have ran into a problem on my first attempt at putting theory into practice and would really appreciate any help. I have made two diagrams / images showing the circuit I made I have attached them to this post. I am using an Arduino Uno as a power source.... I ran a 5v positive from the 5v pin on the Arduino using solid core jumper to the top of the breadboard onto the positive row / rail and a negative / ground jumper to the bottom of the breadboard. In the middle of the breadboard I placed a 1k ohms resistor bridging the gap / grove/ divide and ran the positive feed through it and on to the anode leg of the LED. The cathode leg of the LED was connected to the negative row / rail completing the circuit. All works as it should because of the high resistance from the resistor the LED barely lights and is green as it should be. So without using a multimeter I know and can see the resistor is clearly working. However if I move the resistor so it's still on the same line / row as it was but no longer bridging the gap the LED goes super bright and turns yellow which means that the resistor is no longer working which I can't figure out why because I know there is definitely current flowing through it given the extreme reaction of the LED. I vaguely remember reading somewhere on these forums that Fritzing is not liked very much so I hope no one minds but to help explain what I mean above I have created two diagrams / pictures using Fritzing. The images diagrams shows the resistor "bridging" and working and the other shows it not bridging and therefore not working. So my question would be why given the resistor has current flowing through it does it not work unless it's bridging this middle divide / gap / grove? It makes me think I am missing something really stupid that everyone should know about breadboards but just seems really odd to me. Many Thanks Rab

Topic by belfastrab    |  last reply


Matching 700mA constant current driver to 20mA LEDs? Answered

Hello all: Ultimately I'm trying to drive upwards of 100 3mm white LEDs in an art project with dimming and a connection to 120v AC power (this is for a chandelier). I've been playing around with some constant current IC driver like the Supertex CL2 as well as 5 and 12v power supplies but I've been looking for a dimmable solution with a small form factor. I picked up a Robertson constant current LED driver but it outputs at 700mA, I assume because it's intended for 1W or 3W LEDs needing the higher current. Is there a circuit design that I can use like a current divider to drive smaller loads with this supply? My current thinking is as follows: 1) I could simply load 35 parallel strings of LEDs since 700/20 = 35 (of an appropriate voltage drop probably between 9v-15v) and rely on the equivalent resistance of each string to act as a defacto current divider. 2) I could do the same thing but with an in series resistor of some value for each string, the constraint being that increasing the resistor will reduce the number of parallel strings and I may need relatively high wattage resistors if I'm driving 9+volts of LEDs on each string. 3) I could do a smaller parallel current divider, but I'm not confident in my math analyzing the ratios of the resistors to achieve this (for instance if I had only two parallel loads and one was drawing 20mA and the other the balance of 680mA the resistors would have to have the same (inverted) relationship i.e. 34:1...to say nothing of the wattage through the 680mA line, which might be as high as 6-8 watts depending on voltage. Is that right? Are there any other clever solutions I'm not thinking of? Obviously I could buy a lower current driver (and I may ultimately)  but even the lower current options are at 350mA, so the same problem will exist at a smaller scale. Thanks everybody for thinking about this, I look forward to seeing your thoughts!

Question by michael.pokorny.54    |  last reply


Small variable power supply from car charger?

A friend of mine gave me a bunch or car USB charger used in his company to charge the tablets and phones the delivery drivers use. His problem was that they ordered 10 exclusive for Apple products and 15 generic ones that have the standard 1amp/2.1amp USB outlets. I was asked to take a look and see if the problem is easy to fix. Long story short it was as apart from 2 blown fuses they all suffered from bad solder connections for the cigarette  lighter contacts that failed. Anyway I looked the chips up used to regulate it all and to my surprise the datasheet said they are "variable" from about 0.3V to the max supply voltage of 32V or even 40V. Checked two of mine and same story for one, the other is dirt cheap unregulated and only used to charge a flashlight. But it made me wonder... Since the output voltage is created with a simple resistor divider giving the right feedback voltage it is very easy to adjust them to whatever might be required. Could be a far better option than our standard adjustable voltage regulators and easier plus cheaper than building your own circuit. All the benefits of short circuit protection, under voltage shut off and self regulated max power to prevent overheating for 5 bucks from the next china shop. Give it a go one day before you power wasting old school regulators ;)

Topic by Downunder35m    |  last reply


Measuring DC Motor Load Resistance - Selecting the Right Switching Transistor

I am an electronics noob, although I have done several Arduino based circuits, the stuff I have done is all a bit "painting by numbers" and I feel the need to understand more about what I am doing. I have searched the internet for an answer but can't quite get all the info I need. Time to ask for help! I am building a circuit (without a microprocessor) where a PIR sensor will start a small 3v DC motor (from the junkbox) when the sensor is activated (PIR output pin goes high).  The most helpful page I stumbled upon so far (because I think I understand it) is here: http://www.kpsec.freeuk.com/trancirc.htm#relays Under the heading: Choosing a Suitable NPN transistor, where it  gives a procedure for selecting a transistor. The first step is to ensure that the transistor's maximum collector current is greater than the load current, where load current  is calculated by dividing the supply voltage by the load resistance. The thing that is tripping me up is: how do I measure load resistance of the motor? My hunch is that I just measure  the resistance across the positive and negative terminals of the motor whilst it is disconnected.  Can it be that simple I ask myself. I appreciate, I could just try any old NPN transistor and see if it works, but that will leave me no better off for the next time. Thanks for any help you can give, be they  answers or other places to look! Softy Squirrel

Question by SoftySquirrel    |  last reply


Using a hall effect sensor with TL494 pulse width modulator.

I have an electric billy cart with a dead controller board. I constructed the kit circuit below to replace the dead board and it works well enough for the job except for one small problem. The throttle on the billy cart utilizes a hall effect device and not a pot. The billy cart also has a handbrake with a switch that closes when applied. I use this with a resistor to discharge C2 and pull pin 4 (inhibit) high. This ensures a gentle start (as the capacitor slowly charges through the 100k resistor) if the brake is released with the throttle advanced. The output range of the throttle is 950 mV to 4.1 V if VREF (5V) is used as the supply. (I'm dropping it in in place of the pot.) 4.1 V is sufficient to achieve the maximum 90% duty cycle of the chip, but 950 mV leaves me with a minimum duty cycle of about 21%, and of course a motor that won't stop. Will changing the divider ratios 20k/2k2 & 47k/47k be sufficient to get me zero speed or am I going to have to do something more exotic? Thanks in advance.

Topic by Rasputin182    |  last reply


Capturing Audio using ESP32

I'm building a modest wall of lights with an ESP32 and dozens of ws2812b leds and thought wouldn't it be cool to set it up as spectrum analyser. I was thinking of having bluetooth speakers with an aux out, pair them to my phone and hook the aux out to the ESP32 to analyse the audio and drive the leds. Of course, it's not that straight forward so I thought I'd break it down into smaller tasks - First off hooking up the aux cable to the ESP32Amanda’s explanation of her op amp circuit proved very useful as a starter for 10 but I'll need to make some changes .First off, I need to lose the 9 volt batteries. To do this I believe I can replace the TL072 dual op amp she used with a TLV2372 dual rail to rail op amp. (Keeping it dual just in case I go stereo) The rail to rail feature allows me to use my currently available 5 volt supply rather than needing a higher voltage from the batteries Dan also pointed out in the comments, that the circuit is an inverted amplifier rather than a non-inverted amplifier. I checked out op amp circuits on Wikipedia And It turns out he was right – good catch Dan He’s obviously very smart so I also went along with his other suggestion of strapping the opposing input to ground with a 10k resistor to reduce noise For this project I don’t wish to use a mic and will be replacing it with an aux in jack so there is no need to give it any power. The amplitude of the voltage will be about half that of Amanda’s microphone but we have the variable pot to crank up the amplitude. Finally I’ll be replacing the Arduino with an ESP32 to perform the sampling/analysis of the signal. It’s faster and has bags of IOT features but I’m concerned I’ll need to make yet more changes. The Arduino ADC pin has a range from 0 – 5 volts whereas the ESP32 has a range of 0 - 3.3 volts. Thankfully we have the variable pot to adjust the amplitude to say 1.5volts . And for the voltage divider we can take advantage of the 3.3volts provided by the ESP32 dev board so there is in fact no need to adjust the resistors as the 100k/100k split gives us the desired 1.65 offset voltage. That turned out to be a lot easier than I expected So the circuit now looks like this Well done for reading down this far! Let me know if you see anything I may have missed or perhaps direct me to a similar project where I can pick up more tips Thanks

Question by CharlesGoodwin65  


Operational Amplifier input voltage affects other input?

Hello, I have created a simple circuit where 2 10k resistors make a voltage divider. Supply voltage is 12.5V and if I measure in between the 2 resistors, I'm getting 6.3V. Great! Now I connect that 6.3V to the +input of an OpAmp. Result: the value is still 6.3V. Great! (The OpAmp is also fed with 12.5V) Now I connect the -input of the OpAmp to the supply voltage (12.5V). The voltage in between both resistors suddenly changes from 6.3V to 10.1V. NOT Great! Now I connect the -input of the OpAmp to ground (0V). The voltage in between both resistors changes from 6.3V to 2.4V. ?! The output of the OpAmp is not connected to anything. I thought that OpAmp inputs, in theory, have infinite resistance? The datasheet of this OpAmp (LT1253) sais the input resistance should be 10Mohm I also tested this same thing with the LT1497 and the results are the same. When the -input of the  OpAmp was connected to 12.5V, I measured the current going into that pin, 39mA!! (Only measured on the LT1253) What's the problem here? Are both OpAmps broken? Or is there something about the way OpAmps work, that I clearly don't understand?

Question by DELETED_Electorials    |  last reply


Having trouble measuring voltage with arduino.

I have posted this question before but I’ve made a few changes with my circuit with no luck. I’m trying to make a variable lab bench power supply with an lcd screen to read voltage and current while adjusting them. I’m using TL431 to have a 2.5v Vref and  a op amp in voltage follower configuration with 10M and 1M trimmer (Divider) on the input to finely calibrate 38v down to 2.5. The op amp is acting like a buffer. This is the code I've come up with: float volt; int sum = 0;                   unsigned char sample_count = 0; #define NUM_SAMPLES 10 void setup() {   analogReference(EXTERNAL);   Serial.begin(9600); } void loop() {   while (sample_count < NUM_SAMPLES) {    sum += analogRead(A0);    sample_count++;    delay(10);     }    volt = ((float)sum / (float)NUM_SAMPLES * 2.5) / 1023.0;     Serial.println(volt * 15.2 ,3);     sample_count = 0;     sum = 0; } Parts list: LM358 (for now, will upgrade to a unity gain stable op amp) 10M 5% resistor 1M trimmer Arduino Mega (Will use a pro mini in the final circuit) Breadboard (Will this effect my readings?) TL431 (2.5v Vref) Yes I now the LM358 is not suited for this application but I don’t think this will affect my readings by much, about 5% maybe. Will it? This code is gives me OK values at start but when I start to decrease/Increase the voltage. It lags behind and offsets by 1-2 volts on the reading. My goal with this project is to read (LIVE, meaning while changing voltage with buttons and see it change without any offset/lag) Voltage with a resolution of +-5/10mv accuracy and also read current (But thats for a later day). One last thing, I’m 16 so a lot of electronic terms tend to go over my head so please while giving an answer keep it simple if possible. Thanks :D

Question by faraz ahmed khan    |  last reply


Are high power resistors really neccessary on a benchtop PSU conversion?

Was looking through the site and I was just wondering--why all the huge resistors on the bench-top power supply conversions of PC Power supplies? From personal experience this seems like a waste of perfectly good electricity.I know that they require some current to just stay on however in designing a project for my school's Engineering Technology department I found that the heat generated by such a small resistance (Around 10 ohms) was unacceptably high. Originally I was looking at Instructables and this sitethis site for inspiration but all the cooling measures taken to prevent the high power resistor from becoming a hazard seemed rather silly. A few calculations and experiments later with the 250 watt power supply and I determined that 160 ohm1 watt resistors and 1K 1/2 watt resistors were perfectly acceptable for the purpose of keeping the PSU awake and functioning. I connected one of each between each voltage and ground. According to calculations I can get away with dissipating a grand total of two watts or less spread across multiple resistors.The current divider rule dictates that if you add resistances in parallel, the resulting resistance will be smaller meaning more current will flow through the overall circuit. However this increased current will divide itself across the parallel resistances according to the rule Ix= RtIT/(Rx+Rt). The current through and power dissipated by the resistor you've soldered into the PSU will not change enough to be significant no matter how large or small a resistance you attach in parallel with it--with the exception of an effective short and what in God's name are you doing intentionally shorting the terminals of your bench-top PSU? Now several months later, the PSU is still operating happily and powering multiple micro-controller projects on a display board. Therefore I can reliably conclude that the high-power 10 ohm resistors in many computer power supply conversions are probably a gratuitous waste of wattage. You can get away with using a higher resistance and a resistor that dissipates much less current.

Topic by Psickattus    |  last reply


Idea for Social Electronic Art

Hi everyone, I have been working on an idea for a new type of electronic creative art form. Social media has increasingly become cloud and computer-based, enabling people to network and share ideas and concepts online with others from around the world; this community is an excellent example of the power of electronics in fostering shared creativity. Art has always been an important aspect of society, bringing people together through the power of self-expression. In recent years, graffiti parks have become a popular method for communities to express themselves in a constructive way. In the area of electronics, circuitry and robotics have become increasingly accessible through open-source programs such as Arduino, enabling anyone to build complex and beautiful projects in their own garages (or anywhere!). This idea focuses on blending the social aspect of conventional art mediums with the untapped potential of electronic technology. One new technology in particular that has taken the first step towards merging the different fields of creativity is conductive ink and paint, created by Bare Conductive. This graphene-based material enables users to paint circuits and electrical systems onto most surfaces, opening up the entire world as a building area. Essentially, this is the focus of the idea- creative communities making the world their canvas through the power of conductive ink and open-source electronics tools. Imagine the possibilites! Walls covered with lights that can be activated by touching a drawn image, buildings covered with playable arcade games and interactive media, and childrens' parks with community-sourced learning tools on the play area! Of course, there's another aspect here; the social possibilities. See a circuit that someone didn't ever finish, or a piece of electronic art that you wanted to expand? Whip out your Arduino kit and ink bottle, and draw it in! Every wall would tell a story, and it would never stop growing. Our imaginations would be the only limit... What does everyone think of this idea? Let me know any thoughts or input you might have!

Topic by Chikpeas Brother    |  last reply


Trying to run my sony Cybershot from an external 12V supply. Need help

Background: I am currently trying to build a housing that will turn my Sony DSC W-55 Cybershot Camera into a time lapse camera (Automatically take a photo every X Seconds for an extended period of time). I have already built the enclosure that houses the camera, circuit board and actuator that presses the shutter release button ever 15sec. (Adjustable). Pictures below Problem: I Need to run the camera for very long periods of time (current baseline is >8hr, but indefinately would be nice). The camera uses a Sony G-Type Li-Ion Battery that does not provide the runtime I need for this application, so I am trying to hook the camera up to an external supply. The battery has three terminals as follows [+] = ~3.9V    (No surprise here) [C] = 3V         (This is weird) [-]  = 0V I accepted that the extra terminal was strange, but figured it would not be hard to simulate. I used an LM317 Adj. Voltage regulator to simulate the 3.7V [+] Terminal and a voltage divider off of the 3.7V bus to get the 3V required for the [C] terminal. I double checked everything and plugged it in with no success, the camera will not turn on. My question is, what smarts are in the battery that I need to simulate, or is there something wrong with my current set-up. Any help will be appreciated. Thanks, John

Topic by John Culbertson    |  last reply


Input problem with OpAmp-controlled ZVS Induction Heater

Hello, Idea: I'm trying to build a circuit which uses an OpAmp to drive 2 mosfets, which power the LC tank of an induction heater. The idea is to detect when the voltage over the LC tank crosses zero, and at that voltage I would make the 2 outputs of the OpAmp change states from fully on, to fully off. The two OpAmps (both inside one chip) have their positive and negative inputs connected to eachother, but with reversed polarity. This would make sure that one output is high, and the other one is low. Why use an OpAmp? I wanted the MOSFET gate switching to go faster as usually, because in the mazzilli circuit, the gate voltage actually slews at the same rate as the LC tank's voltage slews when it crosses zero volts. In the mazzilli circuit, it actually doesn't switch when the voltage is 0v, but when the tank voltage drops below the gate threshold voltage. This would mean that you are always switching current at 5v (for example) instead of at 0V. So for these two reasons, I wanted to try switching them with an OpAmp. Measurements: Probe I on drain 1, probe II on drain 2, and GND on the circuit's ground, gives me an expected result: when switching states, at 0 voltage of the LC tank, the voltage on one side stays low (since it's pulled to ground) and the voltage on the other side goes from 0v up to 50v, back down to 0v, like a sine-wave. Then the OpAmps switch again, and the one side now goes up to 50v as a sine wave, and the other one stays low at 0v. All good, this is working just fine. Probe I on the one differential input line, probe II on the other differential input line. Since this is nothing more than just a 1/10 voltage division of the previous measurement, I'm also expecting the signal to be exactly the same, but 11x smaller. -> problem: However, this does not happen. Because of some strange reason, as you can see in the scope images: Both channels go high, Twice per cycle, instead of going high only once per cycle, and staying low for the next half of the cycle. This really isn't good! Do the inputs affect the waveform in some way? Remarks about scope images: Image: 2 gates Blue gate voltage seems 'quite' fine. Turning on looks good, turning off is not really good becuse if tends to turn on for a short time once again, before it fully turns off. Yellow gate voltage is terrible. Turning on doesn't happen as expected. Voltage drops back to 0 for a long while which is very bad for the circuit. Frequency seems fine; 50kHz is as expected with the 14µH and 6µF. Image: 2 drain voltages These voltages were measured with a 1-10 voltage divider, and thus show only 1/11th of the actual voltage. This is getting close to what I want the LC tank to do. The voltages seem quite like sine waves. I suspect that if the gate voltages would be as they should be, these drain voltages would also be perfect sine waves. The regular sine amplitude of 50V is as expected, with a 24V supply voltage, but at the moments when the drain voltages strangely drop down to 0v, as you can see in image: '2 gates', at these moments the drain voltage seems to spike over 250V!! Image: 2 differential input lines This is the image which I don't understand. I expect the same wave as in the previous picture, but only 11 times smaller because of the voltage divider. However, the voltage does NOT reach 0v while the drain voltage does, and its shape is also completely different. In this image, both channels are doing one (half) sine wave, twice per switching period. They should be LOW for half a period, as the drain voltages do in the previous image. Better quality images: 2 gates 2 drain voltages 2 differential input lines schematic Datasheets: OpAmp: http://cds.linear.com/docs/en/datasheet/1497f.pdf MOSFETS: http://www.vishay.com/docs/91262/91262.pdf Coils and capacitors: Line inductor value: I'm not sure if this value is correct. Center-tapped main coil inductance: This value should be pretty correct, I calculated it by measuring it's size and windings, and the operating frequency is also nearly the same as the calculated one. tank capacitance: 6 times a 1µf MKP capacitor Questions: - Why these strange large spikes? - Why is the waveform suddenly different when reading it near the differential inputs? For the first time ever, I can provide you with scope images! I finally bought a (quite cheap) oscilloscope. I hope it helps a lot. Oh, and one more thing: The induction heater does actually work already. I'm getting huge currents in the LC tank, since the 6mm copper tubing gets hot after a minute. Water cooling has been added, and it works like a charm! The MOSFETS do get quite hot after 15 seconds of heating an object, or after 40 seconds of heating nothing. This, probably because the gate voltage isn't what it should be. Kind regards, Electorials

Question by DELETED_Electorials    |  last reply


Really, really basic question about resisters Answered

I am building a battery pack out of pouch LiFePO4 pouches 180Ah, 12V charged from a solar charger at 50A. I have an Arduino with ethernet which I am using to monitor it and I'm assembling the circuit board. 2 current measuring boards (1 for charge, 1 for load) and 2 voltage splitters to drop the 12-15V down to the Arduino's 5V max analog in.It's these voltage splitters that I'm puzzled by. The recommendation is to use the lowest resistance to give the results you're looking for. So if I have 12V in, R1, R2, Gnd and R1 and R2 are low value resistors, what's the difference between this and a short? Do resisters limit the current, too?Just trying to figure it out before I start frying components.Mike.Edit: I was a little vague as to the setup. I am fitting out a van for full-time living. This has the LiFePO4 power pack which ranges from 12-15V and a 50A MPPT solar charger. Within the battery's housing, I have an Arduino which is tasked with monitoring what's going on with the power system and sending the status across the network via an Ethernet connection. It should make monitoring it a lot easier than digging it out, opening it up and connecting a multimeter to it! If the current gets too high (or the smoke detector kicks in or the temperature gets too high or something on the network tells it to) then the Arduino can isolate the battery.The current on both the load and the charge lines can be monitored with small current-voltage boards across the ground lines so no problem there. I would like to be able to monitor the voltage in both the battery and the charger so it's really down to converting the 12-15V of the power system down to the 0-5V for the analog pins. Lopping off 10V would be ideal but scaling it with a voltage divider/splitter seems to be how it's done.As you may have gathered, I've been more of a software person and I'm having to learn electronics by finding problems, using my 30-year-old high school physics to figure out what I don't know, looking it up and then either trying it or figuring out what I'm missing.

Question by ImmortalSoFar    |  last reply


Questions about making computer systems from discrete components?

I am interested in building certain components of computer processors with the use of discrete components only. I want to build on the individual component level (transistors, resistors, caps) and not on the gate level (quad and gate or hex inverter ic) and I have run into some problems. I have a few questions and they are large. If you can answer any of them I would be glad but could you number them so I know which one you are talking about. ((1)) My first question is about how to build logic gates with discrete components. I have seen some schematic diagrams for and gates, or gates and inverters; they all seem to have some problems. For example, an and gate might have two bjt's where the base of each is an input. http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/ietron/and4.gif My question stems from the saturation voltage of transistors. I assume that in logic circuits you want a transistor to act as a switch, and thus would want to make sure that the voltage drop is 0. I learned that to do this, you find the resistance value of the load you are trying to run and figure how much current it would take for the voltage drop to be Vcc. (Light bulb has a resistance of 100ohms, Vcc is 10V, V=IR dictates that the current running through the light bulb would be .1A). Then you divide this current by B (gain of transistor) to find the current that needs to be running through the base emitter path. How do you find the load of a computer, where the output of a circuit might run through paths of great or little resistance? Is there a way to make logic circuits with transistors acting like switches while avoiding finding the saturation voltage? ((2)) How are computers made so that they can sit idle and then respond to inputs. This might sound like a stupid question but from a programming perspective the only way I could think to do it would be to create an infinite loop that constantly checks for inputs or a 1 in some input register.  The more I think about it the more it seems possible that this is how computers do it now; I know that the're able to run many programs at once so it seems possible. However, how did early computers do it? If a computer had only the capacity to run one program at a time then it seems a program accepting inputs would always have to come to a halt when an input is requires. Is this truely the only way? How do modern computers accept inputs, how do computers that can only run 1 program at a time accept inputs? ((3)) I am also interested in memory circuitry. Looking at the types of ram, dram seems to be pretty strait forward. As I understand it sram is essentially memory made of logic grates where an outside signal initially acts as an input. The output of the logic circuit is then feed back in as an input and the circuit hold "itself" high or low (this description might be totally wrong). The problem is I have only seen schematics that show sram using CMOS. Is there a way to build sram using bjt's? ((4)) I have also had a chance to look at how rewritable rom (despite being read only) such as flash memory works. My first question is, why is this called read only? I get that it is nonvolatile so it's not ram, but it surely isn't read only memory either! Are there any ways to make rewritable rom with discrete components? Flash involves, to my understanding, trapping electrons with some kind of tunneling. As far as I know, this can only be done in silicon. If I were to make some sort of computer (or more accurately: a device that demonstrates the properties of a computer) would the non volatile memory be limited to non-electrical things (brain, punch card, magnetic memory)? ((5)) How are jumps done in the opcode level? Assembly has specific commands for different types of jumps. Lets say you are running an 8 bit computer that had 8 bits of memory at each address, can't you only address 256 addresses (0 to 255)? Lets say the 8 bit computer processor has 128 unique operations, and an unconditional jump happens to be the 100th operation. In the memory you write your program to, the jump would be written as 1100100 (100 in decimal, the jump command). There would only be 1 bit left, hardly enough room to write the address of where you are actually trying to jump to. My only conclusion is that you would tack a 0 to the front of the jump command making 01100100 and filling up the whole byte of memory. Then, when the computer reads the byte it recognizes the opcode for unconditional jump and reads the next byte of memory as the location of the jump and not  as a specific jump. Thus if you were trying to write an unconditional jump to address zero, the program would look like: ........ ........ 01100100 00000000 Is this how computers perform operations containing operational code and memory addresses that are written as one line in assembly code? Thanks for your time and help!

Question by seanroberts    |  last reply


how do you make a voltage splitter to dividea current in two so they act as if they were coming from different sources

Hello, i am building and rc tank that uses 4 relays to power 2 motors in both forwards motion and backwards, all running from 1 battery pack. however ive hit a snag in my developements in which the single battery pack was actually bypassing the relays as it connected to the terminals of the motors, therefore not allowing me to use one relay to apply +/- power the motor via the battery and useing another to apply -/+ via another. my only logical solution at the time was to remove 1 of the 3 battery packs being used (were each batpack contains 10X1.2v 3AH AA batteries), and arrange it so that 1 pack powerd the motor when going in reverse, and the other two were to power the motor going forwards, and although this means that my tank would run fine, and the subtraction of 1 pack doesnt make a difference power wise to the motors as they run at max efficiency with 2 packs, its still a real hassle to recharge them as i cant just charge em all up at once, the reverse motor battery pack may run out before the forwards, and vice versa, giving me less time to run the tank, than if they were together. so now you know my problem, what i need is a solution, how can i make a voltage splitter or current splitter or whatever, so that it can divide a current in two so that if i were to connect a positive wire from current 1, and negative wire from current 2 it would not complete a circuit, and basically act like they come from two totally different sources. this was what i was doing until i realised that when i tested the motors in either direction, it was actually going forwards each time i switched it on, after swaping the wires around when it would just run the motor if the relays werent even turned on. my tank has nothing yet on its motors shafts like gears or nothing, it was a simple mistake. so please, can anyone help me?

Question by oldmanbeefjerky    |  last reply


Smart amplifier design building blocks help? (making an amp w/ auto-volume adjust by controlling gain with running avg)

I am currently working on a simple headphone audio amp that automatically adjusts volume to my preference, regardless of what video I click on when it is plugged into a computer. I am tired of some video's being so quiet that I have to crank up the volume to overdrive to hear it, while other video's blast out sound and burst my eardrums. And of course when watching photonicinduction videos, he often can be hard to hear his voice at really low volume at like 12 at night when everyone is asleep, but then the sparks and hammers come into the picture, it is often too late to crank the volume back down, and thus makes your ears bleed or waking everyone up in the neighborhood! X-(. (Luckily he has included sound warnings, but I am lazy, and will engineer things that do the hard work of adjusting volume for me! :)   ) In a way, I understand that this will minimize the dynamic range, which I suppose hardcore "audiophiles" will go NUTS over me actually WANTING to do that, but none the less, That is what I want. My design currently is just a simple emitter follower with a NPN and PNP transistor is the class AB operation, and to minimize crossover distortion and give a definite gain, I have negative feedback op amp from the output of the totem pole transistor arrangement back to the inputs that feed the base of the low and high side transistor. (obviously, the transistors by themselves are low impedance output, (CV mode) and high impedance input, and have a gain of like 1.) Sorry, no schematics, but you capable of googling it if you want to see what I am describing. As it is, it works fine. HOWEVER, it does not do the automatic volume, or gain control. That is set in stone by a resistor divider network between the feedback and ground (the basic non inverting amp feedback config.) I do not want a fixed gain. I want a electrically adjustable gain. The thing I plan to use to do the automatic adjustment would be a peak detector on the input, which is probably going to be a simple diode and capacitor with a buffer, and a discharge resistor (or constant current drain) across the capacitor to gradually lower the max output, or possibly an integrating op amp that effectively takes a running average. The output of that needs to control GAIN of the primary amplifier, and I want to be able to control the PID of that thing, maybe by tuning the a LCR circuit, or what have you. It is all nice and analog, just the way I like it! :) If ONLY there was some magical (and common) component that I could control the resistance anywhere in the feedback loop, of with a given voltage w/ respect to ground... I was thinking of like a MOSFET, but I would have to deal with the non linearity of the input vs output impedance, which probably changes with respect to everything from the current flowing through the channel, the voltage relative to ground at the source, the temperature, the alignment of the planet's, what mood god is in, etc etc etc. That is too many factors for an open loop control on to model in discrete stuff! And digital potentiometers are out of the question since, well they are digital, I want an elegant simple solution, and the are $$ and difficult to deal with. They have so many requirements that need to be addressed.  I prefer a elegant discrete transistor circuit, but op amps and other basic building blocks are acceptable, (this thing I want to be built over a weekend with with jellybean parts from by junk bin.) if you happen to know of a specific audio chip that does this for me, please mention it, but I will probably not use it, but maybe analyze the internal circuitry and learn how it works.

Question by -max-    |  last reply


New Interactive Collaboration Page & UI (Instructabook - social ible)

Bricobart has proposed a collaboration contest, read more: here. I guess it would be great to introduce the less-noticed collaboration feature of instructables.  Problem: I think one of the main reasons why the collaboration feature is ignored is because it's difficult to use. Difficult in a way that two or more ible members are having a hard time exchanging ideas through email. Emails are are slow and bulky compared to social networking. Also one of the problem with collabs is that the people who contributed to the write-up doesn't show-up on the credits. My Experience: My former classmate and I had the same problem. We both did the same thing, e-mailing. It also took us hours to finish a write-up. Months after my first collab another friend of mine encouraged me to do another collab, this time with the help of Facebook. The chat and group feature of FB blended perfectly with instructable's collab feature. Proposal: I think that it would be good to have a new social collaboration feature in ibles without using Facebook as a seperate medium for planning and for discussing ideas. ____________________________________________ Concept: The concept includes a designated page for social ible collaboration. The page has six main parts, the six main parts are the following. 1st.) Proposal Page: Imagine this as the forum page, it's divided into all the possible channel categories. People can post ideas of their dream project (like starting a new thread in forums).  2nd.) Find Partners: The project proposal threads are now being viewed by fellow ible members (members willing to discuss and build the project). The project proposal thread should have a "COUNT ME IN" button. Those who wants to join the project should press the "COUNT ME IN" button. 3rd.) Discussion Page: Now that you have found fellow ible members who are willing to build the proposed project, it's now time to close the thread. The thread's status is switched to "In Progress", the "COUNT ME IN" button is now greyed-out. During the discussion, collab members are redirected to a new page, the private discussion page. This page should look like a private group of Facebook. In this page, you can share photos, videos, ideas with one another. You can post on the group's wall and comment on the posts. Notifications shall be sent automatically to the "you page" once a member posts something on the group page. We need to know if everyone is ready to build the project. Once everyone has checked the "I'm Ready" check box, the project advances to the next step. *The discussion page can be accessed by fellow collab members anytime.  4th.) Write-up/ Editing Stage: This is where the traditional instructable text-editor comes in. This time with the presence of a  live chatbox, similar to FB. The chat box should also have a "upload/ attach an image" feature.  5th.) Add Contest: bricobart's idea comes in here. Collab members can join regular and special contests (collab contests). 6th.) Publish: The collab members can now publish the guide! Credits should be given to the collab members. Ex. Designer:_____, Builder:_____ , Programmer:_____, etc..... ______________________________________ I hope this helps. If the idea is too blurry, just tell me. I'll make a HTML-PHP dummy page of how it looks like. 

Topic by ASCAS    |  last reply


How to limit welder current (heat)? Answered

Hi All, I admit to being electrically dumb, well one step above dumb, I'm a software engineer not electrical engineer, but I don't even know enough enough to be dangerous yet:) I'm going to be converting an ac welder to dc. It's a harbor freight 90 amp flux wire job, comes from the factory as AC for some unknown reason, but should be DCEN for FCAW welding. There are several walk throughs availabile online. I don't know the rules for linking to other forums, so I won't post a link, but you can google 90 amp welder dcen conversion if you want details. I attached an image of the circuit I got from a post by bluecatfish onweldingweb. I'll be taking the transformer output, running through a full bridge rectifier to convert to rippled DC, using capacitors to remove ripple, and lastly running through a torroid inductor. Another problem with this welder is it only comes with high/low power settings. The low is still too hot and burns through thinner metals.  I want a way limit current further, but maintain voltage for a stable arc. I'll be adding a bleeder resistor to drain the caps, which gave me an idea. At first I thought to use several more resistors in parallel with the bleeder to reduce current. I imagine this might work but be horribly inefficient. It would still use all available power from the supply, just converting some of it to heat, leaving less power for the arc. I've read that adding resistance in series will reduce current, but won't that drop voltage available for the arc? Then I was thinking, I have a motor speed control for a router. I believe this is a pwm. Could it be used to chop the mains input (120v 20a) to the transformer and reduce overall output without effecting voltage(I've read this is 38v 80a in the factory state before my mods)? since I'm adding capacitors downstream, will they just discharge too fast leaving me with ripple/pulsing? If so, how would I slow the discharge rate? (I'm looking at 3x or 4x caps 22,000uF @65v in parallel on a bus bar, so 66,000 or 88,000uF total). Sorry if in not making sense, as I said in the intro, I have a lot to learn, and right now, the more I read, the more confused I get. Edit:  After more research, and to hopefully use correct terminology, I think I'm talking about using a current divider when referring to multiple resistors in parallel to the welding leads. I think I'm referring to a switching regulator when I suggested using a pwm to chop the transformer input. Can either of these work like I'm hoping? Is there a better way, that is relatively simple?  Thanks in advance for your patience and help. 

Question by DonaldF9    |  last reply


Arduino knock sensor with a twist

Hey there! I live in a dorm and there's no preinstalled doorbell so i thought i'd do something funkier. I've used the stock Arduino Knock code and modified it a bit so agitating the piezo will make a connected buzzer beep. The problem is that while the entire setup is working, the buzzer itself is very very quiet. With a pure tone making script the buzzer will make a loud BEEEP, but combined with the knock code it's extremely quiet. I'm new to Arduino's so please bear with me when i show my code (most is copy/paste to fit): /* Knock Sensor      This sketch reads a piezo element to detect a knocking sound.    It reads an analog pin and compares the result to a set threshold.    If the result is greater than the threshold, it writes    "knock" to the serial port, and toggles the LED on pin 13.      The circuit:     * + connection of the piezo attached to analog in 0     * - connection of the piezo attached to ground     * 1-megohm resistor attached from analog in 0 to ground    http://www.arduino.cc/en/Tutorial/Knock       created 25 Mar 2007    by David Cuartielles    modified 30 Jun 2009    by Tom Igoe  */   // these constants won't change: int speakerPin = 9; int ledpin = 13; const int ledPin = 12;      // led connected to digital pin 13 const int knockSensor = 1;  // the piezo is connected to analog pin 0 const int threshold = 10;  // threshold value to decide when the detected sound is a knock or not // these variables will change: int sensorReading = 0;      // variable to store the value read from the sensor pin int ledState = LOW;         // variable used to store the last LED status, to toggle the light void setup() {  pinMode(ledPin, OUTPUT); // declare the ledPin as as OUTPUT } void loop() {   // read the sensor and store it in the variable sensorReading:   sensorReading = analogRead(knockSensor);        // if the sensor reading is greater than the threshold:   if (sensorReading >= threshold) {     // toggle the status of the ledPin:     ledState = !ledState;       // update the LED pin itself:            digitalWrite(ledPin, ledState);     buzz(9, 2500, 500); // buzz the buzzer on pin 4 at 2500Hz for 1000 milliseconds   delay(100);    }     // delay to avoid overloading the serial port buffer } void buzz(int targetPin, long frequency, long length) {   long delayValue = 1000000/frequency/2; // calculate the delay value between transitions   //// 1 second's worth of microseconds, divided by the frequency, then split in half since   //// there are two phases to each cycle   long numCycles = frequency * length/ 1000; // calculate the number of cycles for proper timing   //// multiply frequency, which is really cycles per second, by the number of seconds to   //// get the total number of cycles to produce  for (long i=0; i < numCycles; i++){ // for the calculated length of time...     digitalWrite(targetPin,HIGH); // write the buzzer pin high to push out the diaphram     delayMicroseconds(delayValue); // wait for the calculated delay value     digitalWrite(targetPin,LOW); // write the buzzer pin low to pull back the diaphram     delayMicroseconds(delayValue); // wait againf or the calculated delay value   } } If i get this working i'll see if i can make an instructable out of it (and make a "secret knock identifier"). I ended up using this code: [url]http://vimeo.com/groups/arduinoprojects/videos/1940394[/url] which works (code can be found by following the links) And it works! I'm still wondering what was wrong with my (pasted) code though.

Topic by Eirinn