# COMMUNITY

### D.C input resistance of a BJT transistor in C.E configuration?

What will be resistance across base and emitter of BJT in C.E configuration

Asked by deepakmurali 6 years ago

### Resistance is Futile

Do you agree with the saying, Resistance is Futile? It can be applied in anything, politics, electronics, etc.

Posted by starwing123 9 years ago

### what is connection for variable resistance having 3. pin. pls tel me where supply and load connected.?

Asked by vijaysinha 6 years ago

### Help with Resistance formula. Answered

How to find the voltage after adding a resistor with the resistance formula? For example I have a circuit that uses 0.975A and I add a 1000ohm resistor to it, if its powered by 220v main then according to V=IR what should be the voltage drop due to the resistor?

### capacitor resistance

Why is it that as super capacitors capacitance goes up the internal resistance goes down? I'm looking for a tiny capacitor that can supply 0.3 volts20mA (I'm going to be powering flexinol, not an LED) for 1 second. I don't want the capacitor to be huge because I'm making a beam bot where size is a factor for charging time and because of it's physical size.

Posted by guyfrom7up 10 years ago

### How to create motor or generator resistance system for exercise machine?

Researching a method to use resistance from a motor or generator for an exercise machine.  There is an axle from which both foot and arm levers extend, so there is rotation, but only about a half turn in each direction, so very low speed, and back and forth.  I have used magnets and eddy current and flywheel from exercise bikes, geared up with a belt.  This works ok, but does not provide enough resitance even when magnets are adjusted very close to flywheel (due to low speed of rotation). I hope to find something already built and available for a similar application, but can locate parts and build it if I understand how.  Resistance must be variable from low to very strong and controllable so user can adjust it.  I have DC motor, and shorting the cord greatly increases the drag, but how do I vary/control it?  Would adding resistance between the wires in the cord increase drag and make it harder to turn?  I have experimented with this and it does not seem to have an impact.  Thanks for your help.

Asked by zanimann 5 years ago

### Really basic Resistance / Amperage question:

Before I begin: yes, I should know this already, but I'm really sleep deprived right now, and therefore slightly muzzy on my electronics knowledge... My circuit has two loops running in parallel off one, limited, 18v power supply: [*] Loop 1 requires the majority of the supply's power to run [*] Loop 2 is simply a 7805 voltage regulator supplying 5v to an analog input on an Arduino, so needs almost no current running through it. [*] when Loop 1 and Loop 2 are both active, Loop 1 does not get enough power. if I place a resistor in Loop 2, in series with the 7805, will it increase the amperage to Loop 1? I think the answer is yes, but, once again, I'm MASSIVELY sleep deprived. any help is appreciated.

Posted by gschoppe 9 years ago

### LEDs in resistance sensitive circuit

My question is relative to getting a LED to function correctly in a resistance sensitive circuit.  Here is the situation. 1. The Battery Warning Light in an automobile I am restoring currently uses an incandescent bulb.  2. Functionally, the light is on when the ignition is turned on, but goes off when the engine starts.  3. This works fine with the incandescent bulb, but not with a LED, even if I put the same incandescent bulb in the circuit (parallel). 4.With just the LED in the circuit, it never goes off.  This is because the circuit has about .5V leakage voltage through the device (which is a Lucas 3AW Warning Light Unit) when the engine is running (and correctly, 12V when just the ignition is on). 5. With both the LED and the incandescent in the circuit, the incandescent does not come on and the LED does not go off, both with ignition on and engine running. 6. I have also put a potentiometer in the circuit with just the LED and cranked it from 1 Ohm to 100K Ohms, with no effect. 7. Of course, an easy answer is to just use the incandescent, except that the dash is wired and complete and installed, and I prefer to get the LED to work.  Any thoughts or suggestions would be very much appreciated.

Posted by DaleR18 2 years ago

### How to control the Voltage, Current and Resistance in a circuit?

I've seen devices which do this but I don't know the name of it?

Asked by ShanL3 6 months ago

### How to add magnets to magnetic resistance exercise bike to increase resistance?

Hi, and thanks for reading my question.      We have just bought an exercise bike, it uses the pedalling to power the magnetic resistance of the bike. Here is the problem: at the highest setting, the resistance is still not very much.  We think that maybe we can increase the resistance by putting a strong permanent magnet near the flywheel, (we would cut a hole in the plastic cover to put the magnet near the flywheel). Can someone explain how to figure out how strong a magnet would need to be? How much "pull" would probably have a significant effect? What type (neodymium?), and what shape would work best (disk, rod, etc...?). We are willing to put about \$50 into a magnet.   If this doesn't work I think I will remove the cover and just use a "friction wheel" sitting on top of the flywheel. really ugly, but it should work. Thanks for any help you guys can give!

Asked by Urrgghh004 2 years ago

### New Antibiotics.

Antibiotic resistance is becoming a real problem, and I figured that the crafty and scientific community could help. https://petitions.whitehouse.gov/petition/help-fund-and-add-incentive-drug-companies-create-new-and-better-antibiotics-fight-rising-super/nwTTbVX3 I started this petition on the white house website. Note: This is at no benefit to me, I am just trying to bring awareness to this issue.

Posted by airsofter1 4 years ago

### Simple Resistance Question

I am wiring some LEDs in series-parallel using a 9v battery. The schematic I've been looking at online as a reference shows resistors being used but doesn't say what size. Here is the layout: |-- LED -- LED -- LED -- resistor?--| |-- LED -- LED -- LED -- resistor?--| |-- LED -- LED -- LED -- resistor?--| |--9v-----------------------------------------| I assume it's a simple calculation but I haven't worked with this stuff in a few years. Thanks in advance.

Posted by L3fty 6 years ago

### How does one make a reverse photocell?

How can you use a photocell to make a circuit whose resistance is proportional to incident light? I'm looking for an open circuit in the dark and a short circuit in lighted conditions.

Asked by EEWolverine 4 years ago

### reducing current on a power supply

So I am trying to reduce the on the current power supply I have from an old router. The out put is 12v DC 800mA (.8A). I want to use it to run a man 12v .3AI just wanted to make sure I did my math right and to make sure I didnt miss anything.Ohms LawI = V/RR= V/I V = 12 I = .812/.8 = 15 ohms resistance in theroy_Current on the fan is .3 A, I am assuming that is the max. So desired current is .25I = .25 V = 12 R is current resistance, X is additional resistance Q=(R+X)I = V/QQ= V/IR+X = V/IX = (V/I) - R V = 12 I = .25 R = 15(12/.25) - 15 = 33 ohm resistance neededSo I would need a minimum of 33 ohm resistor. Am I correct?Sorry for the explicitness of the math, its been drilled into me to show every step.

Posted by dragonkeeper117 8 years ago

### what type of resistor should i use if i have 3 of these LED's in a series with a 12v batter?

LED Specs Size (mm) : 5mm Lens Color : Water Clear Reverse Current (uA) : Life Rating : 100,000 Hours Viewing Angle : 180 Degrees Absolute Maximum Ratings (Ta=25°C) Max Power Dissipation : 80mw Max Continuous Forward Current : 24mA Max Peak Forward Current : 75mA Reverse Voltage : 5~6V Lead Soldering Temperature : 240°C ( Operating Temperature Range : -25°C ~ +85°C Preservative Temperature Range : -30°C ~ +100°Cï»¿ and i'm using a B3v-250c   3 LED array to hook them up that i bought from ebay

Asked by JustXtreme 8 years ago

### Resistance calculator using flash

I just created a resistance calculator using liveswif (its like macromedia flash only not as good) and programmed it with actionscript.   I can't figure out how to get the numbers to line up properly, although the calculator still works.   If you have a resistor and need to find out how many ohms it is, the calculator will do it.   http://www.gamesfree4u.com/resistancecalculator.html

Posted by pennsteve 8 years ago

### cutable laser?

I know scientist have created lasers that can cut but how much money would it take to make one? and what materials would be need? and... what kinds of materials would be laser resistance, not effected by a laser... or would that depend on the lasers stength?

Asked by saiyankev 5 years ago

### Must have capacitors, resistors, transistors

I am wanting to know the best values/ most used values in electronics projects for resistors, capacitors, and transistors. Suggestions? Also when purchasing capacitors, ceramic vs. electrolyte? Are ceramic mostly for lower capacitance values? And lastly what is the difference between a 10k resistor and a 10 Ohm resistor. What I have figured out is that the 10k is a higher resistance value.  Thanks, diamondmine

Posted by diamondmine 3 years ago

### Diode question

I need help with diode. Actually a question: if you put diodes in series for example 2 diodes of 300 V will they act as one diode of 600 V?

Posted by Dantex 9 years ago

### LEDs and resistors

I notice a lot of people tell you to always put a resistor on an LED. Should I use a resistor if my LED's forward voltage is the same as my power supply?

Posted by bomberman3 9 years ago

### Help finding adjustable and slip resistant material!

I am working on a project where I want to be able to paint with 5 brushes of different sizes simultaneously. For this, I need to build a device that can hold 5 paintbrushes together, one next to another with a 0.5 inch gap between them (so the bristles don't overlap). My challenge so far is to find a clamp or material that can adjust to various sizes of handles while keeping everything still when I push down to paint.  I have tried to poke the brushes through a piece of foam but they will slip and go through (depending on the shape of the brush). Someone suggested duct tape but I'd like this device to be reusable and easy to change between brushes.  Basically, can anyone suggest an adjustable clamp or some better material that can fit various diameters and hold still?

Posted by Julep 3 years ago

### What do 1/4, 1/2, 1 or 5 watts values mean on a resistor? Answered

I know that this is such a basic question but what do those values mean when selecting a resistor?

Asked by blkhawk 6 years ago

### Dimming Leds and Potentiometers

Looking for a formula; I have a 24v 1.7 amp power supply ( http://www.allelectronics.com/make-a-store/item/PS-2417/24VDC-1.7A-POWER-SUPPLY/1.html ) to light 2 - 24v led strips ( http://www.allelectronics.com/make-a-store/item/LBR-24/24-WHITE-LED-LIGHT-STRIP-24VDC/1.html ). I want to be able to dim the led's from full power to completely off, but don't know how to calculate what size of potentiometer would give me the right ratio for dimming. IE, I don't want the LEDs to be completely off when the pot is only halfway turned. The urls are links to the exact products I purchased. Also, the power supply seems kind of large, and I still have to enclose it, so if anybody knows of a better and cheap path to get 24v that involves a little less potential for death, I'm all ears. Thanks!

Posted by bctour7 8 years ago

### Circuit Design Questions - Voltage Drop Answered

Hi there, I'm working on a circuit which will include a 3v, .7Amp motor and three 20mA LED chips, with a maximum forward voltage of 3.8v. The whole circuit is intended to run off a 6v battery.In calculating resistance for voltage drop, I've figured out that resistance for the motor is 2.1 Ohms and then (by Ohm's Law Resistance = Voltage / Current) the resistance of each LED chip is 190 Ohms. Is this correct? It seems astronomically high.?

Asked by Zahv 5 years ago

### I need some help with comparators. Answered

Upfront I apologize if this seems like a dumb question, but both Instructables and google have turned up nothing useful for me. I have a need for a resistance comparing switch circuit. I can't find anything about resistance comparators anywhere except articles that you have to pay to read. I need something that will compare a set resistance to a resistance that will vary, I want it to switch off when the tested resistance is higher then the set one and off when its the reverse. I have no clue what to do.

Asked by The Ideanator 8 years ago

### How do I find the right resistors for a Marx generator? Answered

I am wondering how to calculate the needed resistance for the charging resistors on a Marx generator

Asked by Mecknavorz 3 years ago

### How to operate the Iphone's touchscreen with gloves on.

Now that it's 20 degrees Fahrenheit outside, I normally wear some thick gloves to keep my hands warm. But whenever I need to use my Iphone, I need to slip them off to operate the touchscreen. I heard that the Iphone touchscreen recognizes the electrical resistance of the skin to measure where you're touching it, but I don't know if this is true. I was wondering if there was any method to perhaps simulate the resistance of my skin on the fingertips of my gloves using some substance. The problem is, I don't what to use. Also, if what I heard was wrong, I would appreciate any other suggestions on how to use the touchscreen without taking my gloves off.

Posted by hydrnium.h2 9 years ago

### I need help understanding how to make simple circuits?

I'm very new to electronics, and I want to understand the basics of making simple circuits. For the longest time, I have not understood how people can determine how much power is needed for X amount of LEDs, and how much resistance and so on. Yes, I have taken a physics class, but I'm very rusty on it all :P I hardly remember any of it and I'm hoping the community will help me out. So again to sum up my problem, I need help determining how to make simple circuits that include things like light dependent resistors, LEDs, motors, and simple things like that and especially how do I determine how much voltage, amps, and resistance I will need in the circuits.

Asked by XBLmonster 5 years ago

### Resistor Voltage Drop

Is there any way to calculate the voltage drop of a resistor value? For example, if I had a 47 ohm resistor, would its voltage drop equal -30V, -857358V, or -0.5V?

Posted by puffyfluff 10 years ago

### Should I use Audio-taper or Power-taper? Answered

In circuit bending, should I use an audio-taper Pot, or a power-taper for the bends on the circuit board? Or is there even a difference between the two?

Asked by Zem 8 years ago

### Id like to build a small test tube heater with nichrome wire. Where do I start?

I would like it to be variable from ~100C-400C and have minor experience in electronics.

Asked by GalaxyX 5 years ago

### What's a good Pot size for circuit bending? Answered

What's a good average Potentiometer size for circuit bending? Or is it a good idea to have multiple of different sizes around? Is it anywhere from 500 to 10k? Or 1k - 10k? Thanks!

Asked by Zem 8 years ago

### how to do black oxide at home?

I have some machined steel parts I would like to black oxide to prevent rust and to make look nice. I would like to know the chemicals involved to make the immersion bath for room temperature black oxide.

Asked by high05 8 years ago

Hello, out there, I would like to find how to build a ground penetrating gadget. I think there are a lot of 'us' would like to have something that can 'peek' underneath the surface of the ground, not necessary very deep. For example, such a gadget that can help fossil hunting tremandously. And it does NOT have to go all the way to Ground Penetrating Radar. As long as it can detect the differences between the matrix and interested object up to say 50 cm in depth, it will be good enough. And it doesn't matter what physical principle is used: GPR, ultrasound, electrical resistance or capacitance, ... (whatever). What I have in mind in such gadget would be tied to one of the shoes (so, it must be very light weight), using wifi to transmit the signal to iPad/iPhone so that the user can just walk and know the place to dig. Any help or comment will be greatly appreciated.

Posted by DinoDragon 6 years ago

### How can convert a 12v power supply to 3v?

I am working on a laser spirograph project, I am using 12v dc fans on the inside but also want to power a 3v laser diode off the same source. Does anyone know how I can allow the full 12v to be used on the fans but drop down the voltage for the laser?

Asked by ugman77 5 years ago

### What resistor(s) will I need for my IR LED Circuit?

I'm going on information obtained on the net so please bear with me! I'm intending to use eight 200mw triple IR Leds wired together using a nine volt power source (battery). What resistors will I need and how many? I've already seen a diagram on how to assemble the circuit but some confirmation would be greatly appreciated as the previous threads on the subject were somewhat debated.

Asked by Jman58 5 years ago

### Knex Auger

Resistance, one of the best games on PS3, but has anyone made the auger as i think it probs is the best gun despite it only being a computer game. Anyone that can make one that looks good (number 1) Posts instructions (number 2) and that works (number 3) automaticly gets a five star rating in my opinion

Posted by starscreamstriker 7 years ago

### Capacitance transforms electrical energy into what other form? Answered

I've been working on my understanding of electricity. So I am a little ignorant on the subject. From what I've read, there are 3 fundamental ways energy is consumed in a circuit: resistance (R), capacitance (C), and inductance (L). But that's just the terminology, right? Energy is never consumed, it's transformed. So resistance primarily creates heat. Inductance primarily creates magnetism or a magnetic field. Capacitance??? Capacitance transforms electrical energy into what other form of energy?

Asked by Vorenus 7 years ago

### Anyone know of a resistor that is sensitve to sound vibrations?

Does anybody know of something like a photo cell, except instead of the light being the variable to determine the resistance of a circut, it would be sound and vibrations? If ya do, could ya give me a comment on what it would be called, what they're used in, and where ya could maybe buy one? Thanks! -xD

Asked by ! xD ! 8 years ago

### Christmas Spirit -O-Meter (Bah humbug meter)

I'm a school teacher and every year we have a door decorating competition...and we always lose.  Last year, I tried working on an interactive door display that shows the users holiday/Christmas spirit level, ranging from jolly to bah humbug.  My idea was the user would put one or both hands on a metal plate(s) and lights would show up showing their level of holiday spirit.  Essentially, it's a skin conductivity meter that uses a row of led lights indicating the amount of resistance/conductivity. Does anyone have plans available or can direct me to a site where I can find them.  Preferably nothing too elaborate where I can just use a breadboard and electronic parts from Radio Shack. Thanks, Dwight

Posted by boomfiziks 5 years ago

Hi Guys,   I built a power supply (half wave rectifier) for a project. It simply rectifies normal 120VAC and gives me a pulsed 120VDC output. The resistors are rated for 20 Watts (I calculated that I only needed 4.32 Watts), but they still seem to get extremely hot and I think they are beginning to break down. Is there any way I could put a heat sink on them? Thanks

Asked by transistorguy 7 years ago

### electric shocker resistance and housing problem, i only have a week or two until the secret santa party

Asked by resistanceisfutileiflessthan1ohm 5 years ago

### Specific output of current? Answered

I'm getting a little more knowledge about current measured in mA, but it's still all confusing. From my understanding, your project draws the current needed out of your battery. If my LED uses 25 mA, then the LED will be sucking 25 mA from the battery. If I have two LEDs, then it would be sucking 50mA from the battery, thus reducing its life. So, based on that, how can wall warts have a specific output of amps? How can a wall wart put out 1000 mA? If you use a project that only takes 700mA what happens to the other 300 mA? What if your project use 1,500 mA? And. . . How do you measure the current being pulled through a basic circuit and your average 555 circuit? Thanks,

Asked by HavocRC 5 years ago

### How do I keep my chicken's watering system from freezing? Answered

Hi!  I just found this site and can imagine I will be spending a lot of time here!  What brought me here today is a concern from last winter.  I raise chickens and developed a winter watering system that ALMOST works... It involves 80' of PVC piping that is circulated with an aquarium pump and was heated with a bucket heater.  The water is stored in a Coleman Cooler.  The birds access the water using 10 "Chicken Nipples" (http://www.avianaquamiser.com/chickennipple/) and here in lies the problem.  Even though the system flows in cold weather, the small amount of water in the nipple tends to freeze.  I imagine I could heat the system more, but I would rather have the heat directly on the nipples to keep them warm. I could use a light bulb on each but I would rather be more efficient.  I am hoping for a way to heat a bracket or coil around each one and have it turn on periodically as needed (maybe using a timer and a ThermoCube).  All the heat coils I find tend to produce too much heat and I am afraid of melting the plastic around each of the nipples.  I have spent countless hours at Home Depot, Radio Shack and electric supply stores trying to solve this.  Any help is greatly appreciated!   ---Regards Alexander

Asked by amagnus 4 years ago

What if we charge a capacitor without resistance. What will happen? My teacher taught me that without the presence of external resistance capactors charge and discharge instantly.

### Voltage controlled Variable Resistor??

I'm making a circuit in which a person spins a motor shaft, generating current. The faster the motor spins, the lower I want the resistance to be to a part of a separate circuit. I'm thinking of some sort of voltage controlled resistor I can make. Any instructions? Thanks. ~plmqaz

Asked by plmqaz1243 6 years ago

### How can I limit the RPM of an electric motor by using resistors or trimpots? (cheap/simple way)?

I've done it with a small trimpot that almost ignited by heating. What the problem? The current is to high? To lower the RPM must i lower the current or the voltage? And what exactly do the resistance lower? voltage or current?

Asked by vinacarv 8 years ago

### Gaming system?

I want to get a new system, and I'm not sure if I should get an Xbox360 or a PS3. 360 has a whole bunch of awesome games, and PS3 has free online gaming. I'm not sure which one to choose. Which one is better? PLEASE DON'T JUST POST SAYING THINGS LIKE "Oh ps3 suks" or "I have a 360"

Posted by Farewell88s 9 years ago

### what is rolling resistance in tire?

Asked by thomasraja 9 years ago