Ok,so I get a 3 volt signal from a detector and use this 3 volt to trigger an alarm which atleast need a decent 7 volts to function.The detector could take a max. of 5 volts input which I got from the 7 volts DC supply.This 5 volts fed,gets transformed into 3 volts after the detection.So let me make this clear,I have a 3 volt and a 7 volt supply.I need to use this 3 volt to trigger the 7 volt circuit.I know what you are thinking-a relay !right?but I couldn't get  a 3 volt relay anywhere(though I got a 5 volt relay).I can tackle this situation in two ways.1)Either by stepping this 3 volt to 5 volts and making the relay do the job.but how? 2)Or some circuit to use this 3 volt to trigger the 7 volts(like a relay but maybe by using ic's).This is the final part of my project and so please help me.

I have a small r/c tank that is 6 volts  .the problem with it is it is made to take CR123A 3 volt camera batteries  .which run about 5-7 dollars each  .i could by rechargeable ones for 50 but i thought it would be easier and more cost effective to convert it to run on a nine volt rather then four AA or AAA  .not just do to the cost but also because the space limitations i know how to solder and built circuits if i have a schematic provided .so could anyone provide me with a small circuit schematic or is it just in need or putting a resistor in between the terminals?

I am working on  a project using an aurduino and a relay shield and i want to power it with a 7.2 volt battery like the kind you find in rc cars. i don't know if it will draw too much current and fry the aurduino because that wouldn't be good. is there some way to regulate current without dropping voltage? i have been doing some research on google and found people that have been doing this with an aurduino mega but that has a built in voltage regulator and i kinda fried mine a while back in the project and now i am using a resistor diode pair to keep a solid 5 volts but that isn't enough for the relay shield.  thanks a lot      Harry

How to convert 12volts 7 ah to 5 v 1ah 12 volts can be connected to 7805 for converting into 5 volts but how to convert current. current could be limited through resistor but which? also give formula of how to found it out

I want to make a multimeter out of an attiny85v, and some 7segment leds for a 12volt power supply that I made, I would like it to measure from 0.0V to 12.0 volts, with an accuracy of .1 volts. Anyone know any good circuits? EDIT: This is what I am looking for, except the author has not included any code http://fedetft.wordpress.com/2010/10/02/digital-voltmeter-for-power-supply/

I want to Build a flashlight as small and bright as possible but it doesn't need to last long. I allready got a case i want to use, it has enough space to fit 2 rechargeable AA's and 2 1000mA LED'S + cooling thingy. But to build it I need at least 7-8 Volts (12 woud be better). I only need it for like 10 Minutes between recharging so I don't really care about efficiency. Every schematic and formula will be helpful :) Oh and it would be nice if it's cheap ^^ Thanks from Germany :)

I have multiple solar panels (3V, 6V). I want to build a charger for bicycle, to keep my battery powered lamps (DIY) battery alive. Currently, I use my DIY lamp with a USB Power bank (5,2V , approx. 50k mAh), but my lamp contains 39 LEDs, and they are ultra-bright LEDs, so they drains the battery fast. So I thought if I connect some solar panels to it, I can charge power bank during daytime.

I have used modded computer power supplies many times to power my creations, but in the past I have always relied on just using either the +5V red wires, the orange +3.3V or the +12V yellow wires.  However, most sites that offer advice on diy lab power supplies always say to hook the 12V to the 5V to get the 7V.  My question I guess is do I hook the +12V to the +5V to be the new +7V positive, and then rely on one of the black ground wires to be the negative? Or, is it the +12v  wire hooked up to my 7V devices positive lead and the +5V wire hooked to the devices negative lead?  Any help would be great, kind of stumped.  Multimeter was lent to a friend, and I'm not really in the mood to fry electronics to test it.  Thanks and sorry for the oddly worded question, having trouble following myself at this point.

i have a rechargeable battery that is 7.2 volts and 3000 mAh Ni-Mh now is it safe to add a Voltage Regulator to run an led or if not how do i? what also is scaring me is the 3000 mAh if its good or bad

Can an Atmega328 chip +oscillator run off of 3.7 volts without a regulator to be used for 7 channel pulse width modulation with mosfets to drive the leds? I'm desiring to power it with an 18650 battery. (which charges to 4.2 volts and drains to 2.75 volts) http://www.dealextreme.com/details.dx/sku.5790 if not, how could i do it?

If I have a device that is rated at max 17 amps and 31.5 volts (but capable of operating at any lower amperage or voltage) and I want to run it off a 12v 7amp circuit, will that overload my circuit? Do I need to put a resistor in to limit the load? What if I need to bring the amperage down to 3.47 amps off the 7 amp circuit... do I need to put in a resistor then, or will my power supply just automatically supply only what it can?

I have been working on a laser engraver for some time now, and have just recently gotten the laser parts.  I need to make a laser power supply, which I currently have a 5-volt fixed regulator which turns 15v 380ma into (obviously) 5v with roughly 400ma (value on label is not completely accurate).  I know that diodes will drop ~.6-volts, which I have a line of about 7 of them for testing, giving me 2-volts with the same current.  The problem I'm having is, I put proper resistors into the circuit to give 200ma to the diode, but every time I attach the laser to test the current it always reads 17ma on my volt meter.  Why is this?  How am I able to build a proper laser driver with limited parts (limited to a large supply of resistors and mixed caps, no adjustable regulator)?

1.As you can see in the diagram i have eight 4.5 AH SLA batteries joined together to make four 12 volt 9 AH batteries. how would i incorporate my bigger 7 AH 6 volt SLA into this? 2.Is my math correct that i did up in the corner? 3.Does an amp an hour storage in a battery mean it will supply one amp for one hour? 4.If so and my math is correct i would have 516 watts of power for one hour stored in these batteries?

How many ohm resistor would i need to resist 7 volts to 3.5 volts and 12 volts to 3.5 volts also....

My school exhibition's tomorrow and I need to do something urgent.There's a 7 VDC supply which is converted to 5 VDC by a voltage regulator(both have a common negative terminal).I need a BC 547 to act as a switch and complete the circuit of a device connected to the 7 volt circuit when the 5 volts is used as a signal and sent to the transistor.To put it in another way-The device needs to run on 7 volts when a 5 volt signal is sent to the BC547.I've got about 4 hours of time before I go to sleep(actually forced to!)and the exhibition's tomorrow morning!!!

Can I power an AC LED driver with DC voltage, from what I understand the driver controls voltage and current. I purchase an LED light 7 x 1watt , the driver was rated 85 - 265 volt ac input but the seller had written 12 volt DC with grease pen across the printed label. This light works fine so I ordered 7 more like it with same ratings from a differant seller and they only work on 115 - 230 volt. Now I need to find proper driver or ship back to Hong Kong( Grrrr) I have seen drivers rated at 12 volt AC, will these work on 12 volt DC voltage? Thank you in advance, Duncan. 

Reposting need help Can I power an AC LED driver with DC voltage, from what I understand the driver controls voltage and current. I purchase an LED light 7 x 1watt , the driver was rated 85 - 265 volt ac input but the seller had written 12 volt DC with grease pen across the printed label. This light works fine so I ordered 7 more like it with same ratings from a differant seller and they only work on 115 - 230 volt. Now I need to find proper driver or ship back to Hong Kong( Grrrr) I have seen drivers rated at 12 volt AC, will these work on 12 volt DC voltage? Thank you in advance, Duncan. 

Hi, its me again and i was wondering if you guys could help me. Well i just got this (http://www.nitrorcx.com/brushless-monster-truck.html) electric off road truck and this monster is insanely fast. But i want a bigger battery. In the instructions, it says the trucks input is 7.2 volts up to 16 volts. But thats the problem, my dad and I are skeptical about putting a battery over 7.2 volts in there. I am hoping to get an 8.4 volt battery (http://www.rcsuperstore.com/ProductDetails.asp?ProductCode=VEN15277T&click;=2) like this 7 cell one but am still skeptical about even this 1.2 volt jump. Can anybody tell me if anything  will fry, or be perfectly fine.

Hi all! Whats the best way to get a nice circuit friendly 5 volts from 4xAA batteries? Measuring some brand new AAs, they're about 1.6v when new, which drops under load, I know. So four AAs of course add up to 6.4v, possibly blowing my low current circuit. And isn't a 7805 voltage regulator only good with aroundabouts 7-8 volts source because of how they work? Plus DC-DC converters are expensive, and resistors are wasteful. :-) Thanks!

7 segment sed driver/decoder circuit helpEMAIL FLAGIve looked all over, and have already tried 3 circuits, but none work. They have either the wrong ic, wrong led display, etc. So, I want to make a circuit that, by using a decoder, I can flip 4 dip switches and make the display make certain numbers. I have a 7447 ic, common cathode led display, but I can only either find a circuit with a 7447 and a common anode, or a circuit with a common cathode but a different decoder (a latch/decoder/driver). Here is the first site I tried:http://www.allaboutcircuits.com/vol_6/chpt_7/9.htmlAnd when I finally flip the switches, nothing happens even though I made it exactly as shown. But it has a CMOS, so thats probably a big problem. I also tried this site:http://www.atilim.edu.tr/~hkar/lab5.htmBut it has a common anode, and when I tried it it didnt work. I have exactly ELS321HDB. And I have a power unit that can go from 5 - 18 volts. Can anyone show me how to make this? Im not too good yet at reading circuit diagrams, because I seem to make it way more complex then it should be.

I'm trying to create a digital centigrade thermometer based on an ICL7107 3 1/2 digit 7-segment driver/ADC and an LM35 linear centigrade temperature sensor but I'm having a few problems. There doesn't seem to be much online about using the ICL7107 with a LM35 and most of the schematics available are for volt meters, but that's not a massive problem as the LM35 gives 10mV/C linearly. I'm just trying to go based on the few schematics I have found but I'm wondering about the supporting components for the LM35 which seem a little too simple. The first schematic I found was from a Hungarian electronics forum and seems to depict a diode and amplifier being used for the temperature sensing which seems like a bad idea to me. The second seems more like what I'm trying to do. The other few things are the negative voltage source, the first schematic shows an inverter being used as does the datasheet, but the second schematic shows an LMC7660 voltage converter which seems like a better option to me. The second one does also show three diodes in series used to drop the voltage for the LED displays which doesn't seem like the best idea, but I can't think of a better way to do it without attaching resistors to each one as the number of lit segments will be variable. The supporting components for the ICL7107 seem pretty consistent between the two and the schematic so I'm confident those are correct, but I'm looking for some advice on how to connect the LM35 in a way that will give me an accurate readout. Thanks!

Hello.  I bought some Christmas LED replacement bulbs but they have no specs with them.  I decided to wire one up.   I figured I would go with 1 . 5 volts at 7 1/2 mA.   Using a 9 volt battery, I have a 1K ohm resistor.   9 - 1.5 = 7/ .0075.  My problem is, when I put my meter on it, the one side of the resistor is showing 9 volts, correct, but the other side is showing 3.5 volts.   Shouldn't it only be reading 1.5 volts?  What is wrong?  *I've had the LED lit up for over 25 minutes so far and it hasnt burned out yet. Thank You. EDIT:   I just added  a 10K resistor, so now I have 11K (in series), yet I am still getting a reading of 3.5 volts.   I'm missing something here. lol   I'm also getting a reading of about 9mA with 1K and 11K ohms.   I'm lost.

Hello, I am creating an audio billboard, you all have seen billboards with words, this is a billboard, but there it also talks to you. WHY? Because I am here in Kara, Togo West Africa. In this village they speak 3 local language, and if very educated, they speak French, but if you really wanted them to listen, you would talk in Kabye. I would like to offer free Malaria medicine to people, and this could save babies from dying, 1 in 10 dies that has the Malaria parasite. Mothers avoid going the lab, or taking the cure because it cost one weeks pay, about 7-10 dollars. The longer they delay, the more likely the baby is too weak, and dies. The need to know, money is the problem, but how to tell them, this audio box is to tell them money is there in their own language. But to make it work for one-month, or one year without maintenance is the challenge. I am will experiment with the device inside a Hotel signs, and try to have the Hotel help, they get an ad, and the public ad is served, help them, and they help. The electricity goes off between 3 and 10 hours, sometimes more in Africa, about 200 countries and this box is not close to electricity lines, but next to water pick up spots.  I want to power a 6 Volt Radio I can buy here in Togo, West Africa with a 6 volt motorcycle battery. I am hoping to have the radio run for 10 days, 24/ 7. I can buy a 6 volt motorcycle battery easy, and can even charge it by connecting to a running cycle with alligator clips. But, I need to figure out the correct way to set this up. I learned today, I cannot buy a 6 volt battery charger here: - So I put a diagram down below showing how to make one? Is there a way to know when the thing is fully  charged? http://www.alpharubicon.com/elect/3dollarbattggn.htm What is needed to connect the battery the radio? - I put a wiring diagram with a fuse and diode, is this correct? This is a French speaking country, I speak ok French, but not the word needed to make this device. I need help. Andy Graham of HoboTraveler.com in Kara, Togo West Africa. Thanks

7 SEGMENT DIGITAL BOARD HAVE BEEN INSTALLED IN OUR FACILITY. WE HAVE GIVEN 12 VOLT POWER SUPPLY FOR THESE DIGITS. ITS FACE IS TOWARDS SUNLIGHT. THESE DIGITS ARE NOT VISIBLE DURING DAY LIGHT. PLEASE HELP ME WHAT TO DO

Yesterday my teched teacher showed us an old battery. It looks like a supersized 9-volt battery. it was like 7 inches long or something like that and had a voltage output of something like 75.5 (yes, 75 and a half) volts. I think it's used for old radios? What are these batteries called?

Hello, I am planning on building a stepper motor driver using Tom McWire's design. I want to control 3 motors which are rated for 7 volts, 350mA, and 20 ohms. I plan on using a 12 volt 5amp power supply. I am trying to figure out what kind of resistor I should use so that I do not fry my motors. Maybe I am missing something, but this is the way I am looking at it.... If the motor is using 7 volts and the power supply is 12 volts, that means i have 5 volts left to use. 5v over .35amps (the amount the motor uses) is 15ohms. (14.28 rounded up) That also means it uses 1.75 watts (5*.35). Would a 15ohm 2 Watt resistor be sufficient or am I looking at this all wrong? Thank you for your help in advance, folks :-D

Help, I'm afflicted with inspiration in quantities that exceed my skills!So I came up with an idea for a project that would probably require the use of LEDs, which I know next to nothing about. Ah, said I, the Internet can teach me much... so I turned here and found the (nearly) perfect Instructable, "LEDs for Beginners":https://www.instructables.com/id/LEDs-for-Beginners/Having read this most helpful I'ble, I certainly came away more knowledge than I'd previously had, but still not enough to properly plan my project.Basically, I'd like to create a 2D "array" of LEDs to use as a light source, in order to backlight a roughly 8.5" x 11" translucent panel.It seems like it would be straightforward to just wire up a bunch of white LEDs in series to a power source and a resistor, and be done. I'm not afraid of a little trial-and-error, but I prefer to know at least roughly what I'm doing going in, so I'm asking for your help. Here are my lingering questions:1. Should I wire my LEDs in series, or in parallel? (Or some combination thereof)? In series, I gather that one LED failing will break the whole circuit, which could be a pain. On the other hand, I've seen several projects and sites that cryptically recommend against wiring these in parallel.2. Are there pre-built strips of LEDs I could acquire that would make this project simpler?3. If I want to vary the brightness of my light source, can I use a variable resistor (potentiometer), or does the nature of the LEDs preclude the use of this type of dimmer switch? If so, could I vary the brightness with multiple switched circuits, turning off half the LEDs for half brightness, 3/4 off for quarter-brightness, etc?4. I've got a slew of transformers from old tape decks, telephones, cell phone chargers, etc. Can I appropriate one of these as my DC power supply?5. How do I gauge how many LEDs I'll need, and what density is best to lay them out? I'm looking to create even, diffuse light, with no noticible bright/dark spots.6. Do I need to worry about heat?7. Are LEDs even the correct way to go here? Should I consider fluorescent light instead?I realize these are a lot of questions, but if you're an expert on LED projects, you could save me a lot of research time. If (I build this gadget, it will definitely show up here as its own Instructable.)Thanks!-JD

Ive looked all over, and have already tried 3 circuits, but none work. They have either the wrong ic, wrong led display, etc. So, I want to make a circuit that, by using a decoder, I can flip 4 dip switches and make the display make certain numbers. I have a 7447 ic, common cathode led display, but I can only either find a circuit with a 7447 and a common anode, or a circuit with a common cathode but a different decoder (a latch/decoder/driver). Here is the first site I tried:http://www.allaboutcircuits.com/vol_6/chpt_7/9.htmlAnd when I finally flip the switches, nothing happens even though I made it exactly as shown. But it has a CMOS, so thats probably a big problem. I also tried this site:http://www.atilim.edu.tr/~hkar/lab5.htmBut it has a common anode, and when I tried it it didnt work. I have exactly ELS321HDB. And I have a power unit that can go from 5 - 18 volts. Can anyone show me how to make this? Im not too good yet at reading circuit diagrams, because I seem to make it way more complex then it should be.

I'm trying to hook up a Z-Wave contact sensor to my home alarms wired contact sensor. The alarm panel seems to provide a constant voltage of 6.8 when the door contact is closed and 13.5 when it opens.  The z-wave module I am connecting however looks for no voltage in order for it to be closed and any voltage for it to be open. So how can I only pass the voltage to the z-wave sensor when it goes over 6.8 volts? I have a ground and power wire running to the respective terminals on my alarm panel. I'm thinking I may be able to wire in a resistor but am not sure if that is what I need or what size. Thank you

I'm a Mechanical working in the LED field. I'm trying to design a LED circuit with the little knowledge I have. Here is my circuit in a nutshell: 3.2 Vf typ - 3.6 Vf MAX -.150 mA 24 volt CV PS supplying 3.3 A 7 series in parallel with 22 chains I calculated using typical Vf as the following: 24/3.2 = 7.5 devices so I rounded down to 7 devices in a series chain. 7*3.2 = 22.4 volts required 24 supplied - 22.4 volts = 1.6 volts to dissipate. Resistance = 1.6/.150A = 10.67 ohms Wattage across resistor = 1.6*.150 = .24 W So I found a SM resitor 10.7 Ohms at .25 W. I have a concern with Vf variance. Would this circuit not work if I get Vf's higher than 3.2 Vf? So if I change my circuit to 6 devices per series chain I need 19.2 volts and need to dissipate 4.8 volts. This just seems like a waste.I still do not understand Vf variance. If I design for 6 and dissipate 4.8 volts with a resistor - won't the series chain be starved if Vf goes higher? So how do you accommodate this variance? I just have worries about this design - regardless if I design for 6 or 7. I know some about LEDs but I do not know what happens when I get Vf variance. Does the resistor go at the end of the series circuit? If this is the case then I understand how variance in the circuit would be able to use available voltage - and then the resistor is at the end to disipate what is left over. I've heard concerns that I'm not allowing for more head room #i.e. doubling the resistor value and wattage requirements). If I double the voltage dropped don't I take this away from the LED circuit possibly starving it? I have always assumed the resistor goes at the beginning of the circuit - regulating the current/voltage prior to it entering the LED series circuit.?

I’m working on a project were I have to be able to adjust the voltage of my output by 3.7 volt increments. Example: 12 18650 batteries hooked up in series and have the voltage change from 44.4 to 22.2 to 11.1 Essential I’m trying to go from a 12s to a 3s4p or 4p3s cell configuration.

Hello, Which battery do you think I should buy. I need reliability good performance and long service life. I will be useing them in series with a 250 watt 36 7 amps constant 10+ amp spikes 36 volt electric scooter. I was wondering which is higher capacity at 7 amps discharge and which would last the longest please can someone help me decide :)   http://www.component-shop.co.uk/html/sla12v7ah.html        - 7.5ah kinetec http://www.component-shop.co.uk/html/sla12v9ah.html        - 9 ah  outdo http://www.componentshop.co.uk if the links dont work

I am restoring a 1935 South Bend 16 metal turning lathe.  The original motor was a three phase 480 Volt reversible motor which was operated by the Cutler Hammer 9441H37B  "O" series controller.  I do not have three phase electrical power at my current shop.  I do have a new 110/220 volt, 1.5HP, reversible motor on hand and would like to control it with the current C/H controller and utilize the reversible option on 110 volt power.  I have wired the motor once and it ran well and reversed, however, the motor heats on one end after running for a few minutes.  It is possible I have either a fault in the circuits or I think it is more probable I have wired the motor so that the starting circuit remains energized which would also cause the heating after a few minutes of operation.  I need to know a method or determining the correct wiring diagram for the combination.   There are six wires on the motor, (T1) blue, (T2) white, (T3) orange, (T4) yellow, (T5) black, and (T)8 red.  There is also a grounding connection which I have connected to the gounding connection of the controller. The controller knob has three positions, left, center(straight up) and right. The continuity of the controller connections is as follows; Left Position of controller knob     Center Position of controller knob     Right Position of controller knob (I do not know whether the left or right position of the knob is forward, since the lettering is worn away)  9             8              7                             9              8             7                    9              8             7  6             5              4                             6              5             4                     6             5             4  3             2              1                             3              2             1                     3              2             1  Knob end  (left position)                Knob end  (center position)                  Knob end   (right position)    Continuity of controller                     Continuity of controller                        Continuity of Controller         7, 8, 6                                                    7, 6                                                     7, 5, 6         4, 5, 9                                                    4, 9                                                     4, 8, 9         1, 2, 3                                                    1, 3                                                     1, 2, 3

I am making a college project for science fair, and i have made a generator with DC motor of 24v, 0.33 amp and 7.92 watt. When i rotate the motor it gives 24-27 volt of dc voltage. Now i want to convert that DC voltage into AC by connecting a converter of 12 volt, 7 amp. I have made i rectifier which converts the 24 dc into 12 dc voltage, but when  the converter does not start. Can you please tell me what may be the faults? If the apms  are less, can i increase the amps? If the amps are 0.33 can i increase them to 7 amps?

I used to understand more about electricity and electronics, i swear. I have used the yellow-to-red (+12 to +5 Vdc) method to create 7 volt dc connections for my desktop and xbox fans. I understand the concept of differences in voltage. Do these concepts carry over into negative voltage available on the ATX power supplies?

 I have a small model battery charger which has a resistor burnt out . output is 7.5  volts  according to the label which sounds right as pack is 7.4volts.  measured voltage from transformer  is 15 volts Can anyone tel me what value resistor I need to drop the  voltage  to 7,5 v or whatever the actual out put shoul be. thanks people, john mantova

I have a moped that i want to make led blinkers for it.it gets its power from a magneto so i get ac current.i hooked up a bridge rectifier so i now have positive and negative terminals that i want to hook up to a jumper bar or something so i could run different wires to it.i thought that i should try and work the lights off of a battery. however it puts out between 1vdc when im at idle and 7vdc when im at full throttle.how can i charge my battery with out too much damage

Ok, sorry did not give enough detail.  Looking to make a gas price sign, 3 digit display that can be changed when price goes up/down.  Looking for the digits to be 2 feet in height.  Looking to use 7 - 12" led bars to make up the digit (12 volt).  Need something to control the display besides switches.  thanks for any help 

With most UPS's there is electronic circuitry to reduce the home voltage to 12 or 24v to store in the battery, and then another circuit to raise the voltage back to the home voltage.  I know there is always a loss when attributes of electricity are changed. This seems very wasteful to me. I want to build a UPS for my notebook computer, that I use as a home server.  The power adapter for the notebook creates 19 volts but the notebook itself uses 12 - the other 7 is perhaps used to charge the battery while the computer is on.  I would like to put together a UPS made of 12 volt Ni or LiFe packs - would most likely be 13 volts but I don't think that would be a problem to avoid the double switching of the power.  Can anyone point me in the right direction?

I'm working on a sculpture that involves LEDs.The basic instructions I've been using come from steps 2 and 3 from this tutorial - https://www.instructables.com/id/Beating-... I'm attaching the leads of the LEDs directly to 3 volt lithium watch batteries. However, I decided to try to use a 7-color blinking LED, and I'm having troubles.The LED packaging says it has "single-color, color-changing or flashing modes." The LED has one anode and two cathodes. When I attach the anode and one of the cathodes, nothing happens, and when I use the other cathode, it cycles through all of the modes in about 30 seconds, and then turns off. The only way I can get it to start again is to take the leads off and start again, but this isn't an option for my project, being as the entire circuit has to be covered in glue to waterproof it.How do I get the LED to just blink continuously? Any help is greatly appreciated.

Hi I found this LED bar graph voltmeter athttp://www.solorb.com/elect/solarcirc/vom/index.htmlI want to understand how to build this voltmeter.But please read the solorb website page before posting, for more info.1. What is an offset resistor???2. What is a 'span'(see pic notes)2. For 12v operation,short J2 and J5,but what to do to all the other unconnectd 'J 'wires, just join the wires or what?3.To use without the Blue LEDs, just remove the two LEDs or any other connection/shorting is required????4.What is switch S1 used for ???, I do NOT want to manually push switches while the meter is in operation.5.How to stop the blink-LED mode, I want the constant display mode always.6.There is also two arrows shorting two pins on the IC with words 'Adjust for 12v'?????????7.How to calibrate the circuit accurately???PS:- If you want to know more about a larger part of this project,visit https://www.instructables.com/community/Voltage-Regulator/Kabir

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?

Hello All, I have a problem with a circuit i am building, I use a 2N2222 transistor to drive a Common Cathode big 7 Segment  with a 595 shift register.. I connected a 12v to Emitter, the collector out a 4.7 volts !! How is this possible ? could some one explain please ? Thanks all

Aluminum Base 1” long x ½” Diameter Oil Impregnated Brass Sleeve Bearing 4” long x ½” Diameter Brass Shaft 1 ¾” long x 2” Diameter Brass Rotor 0.10” thick Mica Insulation 0.005” thick Mylar Insulation 0.04” thick Copper Coated Steel Wire (228 U-shaped pieces) .032” thick Copper Coated Steel Wire (12 coils of 11 turns) 0.014” thick Insulated Copper Wire 12 Permanent Magnets ¾” long, 5/8” wide, 3/8” thick o Fe, Isotropic permanent magnet material cooled in a magnetic field, Cast 9100 TS. 450 Brin, 2.2 Peak energy product. ** **magnet specifications: Alnico 4, M-60; 12 AL, 28 Ni, 5 Co, bal Crimped Cooper clips 0.30 thick Copper Tube 2” long x 2 ½” diameters. Acrylic Ring-Dimensions 3 ¾” O.D., 2 ¼” I.D., 3/8” 0.002” thick Plastic Insulation Paper Acrylic holding shapes Acrylic dome Liquid Acrylic                                                 rough parts list Parts List (there is a list of parts suppliers in the next section):

Hi! Can anybody tell me how to convert dc to ac i actually want to convert 9volts dc to 9 - 7 volts ac cause i need to supply this ac voltage to a step-up transformer so that it will convert it into 200volts the real problem is when i provide 9volts dc to the step-up transformer it only gives out 41volts in output but when i gave it 9volts ac from another transformer it gives out 200volts ac and that's what i need but i need it to be battery powered so i need to convert the 9volts dc supply from the battery to 9 or less volts ac that's all i want to ask how to do it!

I don't know why but my servo stops after the fulscan is done. I tryed to find out what's wrong, but it works fine, except the servo. Here is the code. I'm new in this and the timing for the rotation of the robot must be recalibrated, but now i'm trying to make it run. Using arduino uno and sharp IR sensor. the pin 11 is PWM(for both motors, just to slow it down a bit). #include Servo mainservo; float dist[16]; int sensor = 0; int rightB=13; int rightF=12; int leftF=8; int leftB=7; int pwm=150; int pwmp=11; ///====================Functions====================\\ int turnR(){   digitalWrite(rightB,HIGH);   digitalWrite(leftF,HIGH);   Serial.println("turnR"); } int turnL(){   digitalWrite(rightF,HIGH);   digitalWrite(leftB,HIGH);   Serial.println("turnL"); } int turnback(){   digitalWrite(rightB,HIGH);   digitalWrite(leftF,HIGH);   delay(2000);   stopp();   Serial.println("turnback"); } int goforward(){   digitalWrite(rightF,HIGH);   digitalWrite(leftF,HIGH);   Serial.println("goforward"); } int stopp(){   digitalWrite(rightF,LOW);   digitalWrite(leftF,LOW);   digitalWrite(rightB,LOW);   digitalWrite(leftB,LOW);   Serial.println("Stopp"); } int fullscan(){   Serial.println("fullscan");   float volts;   mainservo.write(0);   delay(1000);   for (int i=0;i<=16;i++){     mainservo.write(i*10);     delay(150);     volts=analogRead(sensor)*0.0048828125;     dist[i] = 27*pow(volts, -1.1);     delay(50);     Serial.print("Dist:  ");     Serial.println(dist[i]);     ////////    }   mainservo.write(80);   Serial.println("dir");   while (boolean ang=true){     int d=0;d<=12;d++;     ang=false;     if (dist[d]>20 && dist[d+1]>20 && dist[d+2]>20 && dist[d+3]>20 && dist[d+4]>20){       float dir_ang =(d+2)*10;       ang=!ang;       Serial.print("Angle:   ");       Serial.println(dir_ang);       if (dir_ang<80){         turnR();         delay((80-dir_ang)*10);         stopp();       }       else if(dir_ang>80){         turnL();         delay((dir_ang-80)*10);         stopp();       }       else{         stopp();       }     }   }   Serial.println("FullScan done"); } void setup() {   pinMode(11,OUTPUT);   pinMode(rightF, OUTPUT);   pinMode(rightB, OUTPUT);   pinMode(leftF, OUTPUT);   pinMode(leftB, OUTPUT);   analogWrite(11,150);   mainservo.attach(9);   Serial.begin(9600);   fullscan(); } void loop(){   Serial.println("scanF");   float volts;   float dist;   mainservo.write(50);   delay(200);    volts=analogRead(sensor)*0.0048828125;   dist = 27*pow(volts, -1.1);   delay(50);   if (dist>25){     goforward();     Serial.print("go forward  ");     Serial.println(dist);   }   else{     stopp();     fullscan();   }    ////////////   mainservo.write(80);   delay(200);    volts=analogRead(sensor)*0.0048828125;   dist = 27*pow(volts, -1.1);   delay(50);   if (dist>25){     goforward();     Serial.print("go forward");     Serial.println(dist);   }   else{     stopp();     fullscan();   }    ////////////   mainservo.write(110);   delay(200);    volts=analogRead(sensor)*0.0048828125;   dist = 27*pow(volts, -1.1);   delay(50);   if (dist>25){     goforward();     Serial.print("go forward");     Serial.println(dist);   }   else{     stopp();     fullscan();   }    ////////////   mainservo.write(80);   delay(200);    volts=analogRead(sensor)*0.0048828125;   dist = 27*pow(volts, -1.1);   delay(50);   if (dist>25){     goforward();     Serial.print("go forward");     Serial.println(dist);   }   else{     stopp();     fullscan();   }    //////////// } Any help is welcome.

Hi.I want to make an electret mic and lead into a 1/4 " jack for a phantom powered pre amp. The pre has a low output voltage of approx 6 or 7 volts not the usual 48.Do i need to add the usual capacitors n whatnot??Its a rare old beast from the 80's n i cant locate specs on it n dnt really wanna open it up.Thanks in advance.

Hello there techies, the project USB charger was proposed by me to our professor in physics II. unfortunately he didn't accept such project HOWEVER he was happy. He just said that our project is not yet satisfying. He wants us to do a power inverter. We will buy a 2 6-volts battery and series it and it will output a 200+volts with a 30watts and then we will insert any charger such as a nokia cell phone charger and then voila, it should be charging. Do you think it is possible to do? And another project I proposed is that we will make a REAL TIME CLOCK using a 7 segment. I already had a schematic from youtube. and it uses a decade counter ICs but unfortunately I think such ICs are not available in our country, can you help us sir? T____T 

So i have this transformer that puts out 48v ac. I want to make a variable power supply, and it should put out 7 or more amps. I could use lm317 with a bypassing transistor, but lm317's maximum input-output voltage differential is 40v,  so what should i do? If anyone has ideas how to lower the transformer's voltage 10 volts that would be great.

Hello, Need a circuit design for the following requirement. Checked online available circuit designs but not sure if they meet all needs.  Looking for circuit design as per following details. 1. It will have one or two, 3.7 volts 2600 mah 18650 lithium batteries 2. Batteries will be charged using smart phone mobile charger or solar panel 10 to 20 volts and around 500 mah to 1 ah input 3. Will have mini usb connection for the same on pcb 4. Circuit should have battery level indication. While being charged, when they are fully charged LED should turn on indicating battery full. Also there should be one LED to show that the charging is in progress. When the battery charge drops below specific level another LED should turn on. 5. If we use 2 batteries then they will be connected parallel 6. Output voltage of the batteries should be 5 volts (so step up is required) and current should be appropriate for mobile charging 7. There should be provision for 2 USB connections. Load can be mobile charging / USB mini fan / USB mini keyboard LED (could be 2 at a time) 8. Circuit should be safe enough so no damage is caused to batteries / load etc.