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

Topic by Yerboogieman   |  last reply


I bought 100 leds of ebay a while ago and it came with 100 free resistors. What im not too sure about is what ohm they are. On the ebay page it dosent say if they go with the leds the shop specialises in leds and gives similar resistors with almost every order. All it says on the page is that there perfect for working with 12v or something. I tried looking at those colour code calulators but I still couldnt figure it out. I knew someone here must know. The colours in the pic arent great so I wrote what they are aswell.

Topic by flyer3   |  last reply

Finding the wattage rating of resistors and variable resistors? Answered

Is there a way to find the wattage rating of resistors and such mathematically? or is it something that has to be tested in real life? I have quite a few resistors that I'd like to use, but don't know the wattage rating of them. I only know their resistance, and I could calculate other values if I put voltage across them with a multimeter.  Also, what type of variable resistor would you recommend to control a 12 VDC device that draws 12 amps?

Question by tylervitale   |  last reply

WTF resistors

I just got a back of about 130 resistors for a bag of 50 L.E.D's but some of the resistors ive never heard of, there are a few like 100ohm and 560 ohm but now im getting 1m ohm and 4.1Mohm and 100K ohm,1.5K ohm and 1K ohm. Ive never seen resistors like this before, i am very basic in electronics but i took a class at school have have made many many projects but never resistors like this and i only wanted to use them for a few L.E.D's, I dont really know what im asking for in here but i just sapose if anyone has any help or ideas or really anything with these resistors and matching them with L.E.D'S?

Topic by craig3   |  last reply

help with leds and ohm resistors?

Im trying to make custom headphones from scratch, inspired by the daftpunk helmet of guy, and i want an led lightshow on my headphones. ive been researching how to do this, but ive heard that having an m3 or any kind of audio player wouldnt be enough power to support the leds? ive also heard that if you solder the leds straight to the wiring of the headphones if can create a short, and that placing the led on a circuit chip would help. however i know nothing about ohm resistors or circuit boards. i was thinking i could use an ohm to amplify the power from the audio player to support the leds if its even possible, and running wire through the headstrap to  solder the circuitboards with the leds on them. i need help. alot. any input is wanted, thanks! (ps: - does anybody know how much power i need to run a single blue led?)

Question by gabrielguy   |  last reply

resistor Q

I'm building an LED circuit and I have the right ohm but the W is 1/2 when 1/4 was calculated out?

Topic by mrshow555   |  last reply

resistors and watts

I know how to use ohms law to calculate what size resistor I need but what I really need to know is how to tell/calculate what watt rating I need to use whether it be 1/4, 1/2, 1/8, 1,10 and so on.

Topic by pattyshaw   |  last reply

Laser ohm resistor project question

So I am doing a big modifiction of Kipkay's burning laser project. I am making it into a gun, and the only resistor I can find is a 4.7. Will that do? I have a 5mw module like his, and a 250mw 650nm laser diode. Also I am going to use two C-batteries, so its 12volts total. 

Topic by thedonquixotic   |  last reply

I need a 18 Ohm resistor

Does any one have a 18 Ohm resistor that they could stick in an envelope and send to me because eighteen bucks is a little steep for A resistor. oh ,and radioshack doesn't carry them either :( ~Matt

Topic by iman   |  last reply

What is the best ohm resistor for LEDs?

What is the best ohm resistor to use with a standard led to ensure that it won't burn out? Is it 330? Thanks!

Topic by sciguy77   |  last reply

Is a 1 ohm resistor really needed? Answered

I will be making an LED display. After calculating using the online calculator, I am told that I will need 1 ohm resistors for my series of LEDs. I am thinking that 1 ohm is really not a lot and if I can skip it. Thanks!!

Question by stella_7277   |  last reply

Would I be able to put one 100 ohm 1/4 watt resistor in place of two 50 ohm 1/4 watt resistors? Answered

The attached picture explains my question a little better. Thank you guys!

Question by Jakester98   |  last reply

Resistors on each led? Answered

 I am designing a led array consisting of 17 leds in parallel using 4.5 volt power supply.The led calculator is telling me to use 62 ohm resistor on each - leg of the LEDscould I just use one 62 ohm resistor right after the power supply? Or maybe like 1 or 2 100 ohm resistors? I'm using blue leds 3.3 max voltage 20 Ma

Question by the_burrito_master   |  last reply

My joule thief is not very bright? Answered

My joule thief is not very bright? I've changed the windings, transistor and the resistor; and it is still pretty dim. Help please Parts: 2 different size toroids: Large and Small 3 Transistors: 2n2222, 2n3904, 2n5830 2 Resistors: 1k, 2.2ohm blue led white led with a heatsink Also I used a 20awg and 36awg to make the toroids

Question by daemonral   |  last reply

If you place a 1 ohm resistor across a 12 volt car battery, how much power will it dissipate? Answered

This is one of the exercise from the book, "The Art of Electronics." They do not give answers and i wanted to know if i did it right. I got the answer of 1.44 watts, but i am not sure if this is correct.

Question by cooldude01   |  last reply

3V Resistor and LED

What would be a good Ohmed resistor for an LED running on a 3V power source? 3.2-3.4V typ with a 3.8V max.

Topic by Brennn10   |  last reply

led ohm resistor using a higher resistor to dim please help...Thank you

Hello all' This is the greatest web sight ever...l Love it!! I hope someone may be able to help me out?? I'm very new to working with leds..... I am working on a small project with my son, It has 4 white leds in it and two blinking red leds.  they call for 470 ohm resistors for each led.....But it's way to bright for project?? I tried 1000 ohm and 2200 ohm resistors.  The 2200's gave us the look we were looking for:) My question is.....Will this harm the leds or will to be fine??  Buy the way I'm using a 12 volt ac adapter to run these leds. Thanks so very much in advance!!! God Bless

Question by jimmygman   |  last reply

Ohm's law is calling for a 50ohm resistor. Could I use two 100ohm resistors in parallel or would that be too close? Answered

I'm trying to teach myself resistors through a LED project. My LED's typical FW voltage is 3.5 under a 4.5 supply voltage and a FW current of 20mA. If I've done the math right I should need a 50ohm resistor. correct? I'm hoping to buy the resistors from Radioshack and looking at there supply they only have resistors ranging from 48ohm to 68ohm. I know I could just use the 68ohm resistor, but have also read that wiring resistors in parallel will reduce the resistance. So using two 100ohm combined should work. It just seems too simple and close to Ohm's law's outcome. Would this be safe for the LED?

Question by GodCent   |  last reply

Anyone know what this resistor is? Answered

I am working on the eye controller board of the hexapod robot and it has some resistors on it. The parts list calls for 12 220 Ohm resistors but, based on the photos, there are more that what it shows in the text. The 12 near the top of the board I know are the 220 Ohm ones, but I do not know what the others are. The 2 vertical ones near the bottom I believe are 20 Ohm and the horizontal one closest to the bottom 220 Ohm. The 2 located underneath the 28-pin sockets are half-covered by the plastic. Does anyone have a suggestion on the value of these resistors? I included a picture of the board from the instructable page and circled the resistors in question.

Question by Arya42   |  last reply

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?

Topic by puffyfluff   |  last reply

LED burnout

I've have an LED problem that I have done extensive reading and troubleshooting on but I can't seem to solve it. I'm running 4 super bright white LEDs (NTE30071) in parallel from a 24v 600mA DC wall wart. The LEDs are 4V, 25mA. I need that wall wart to also run a solenoid. When a button is pressed a relay powers the lights and the solenoid for a few seconds. The problem is my LEDs keep dying. At first I had a 10K ohms 1/4W resistor on each and I lost 3 LEDs. After more study and calculation just replaced them with 1K ohms 1/2W resistors. After a few more hours I lost another. When I removed the 10K ohms resistors they read 1K ohms. And I just tested the one on the 1K ohms resistor that went out and it reads 200 ohms. I know there is something that I just don't get; something basic that highlights my lack of any electronics experience. I appreciate any help you can give, this is just is just wearing me down.

Topic by robotninjasquid   |  last reply

Resistors are too warm

Hello,I am building a multi-touch surface using the FTIR method and after the surface is powered for about 10 minutes there is a heated smell in the room, I have noticed that the resistors are very warm and that a couple have started to brown or burn. I really need this table to be able to be safely powered at least 18 hours a day.Here are my specs:LED's:I am using 88 Infrared LED's (T 1 3/4 INFRARED LED, )--8 LED's per series--forward voltage of 1.5v --forward current of 100mAResistors:I am using 2, 10 ohm 1/4 watt resistors parallel (so 5 ohms) with each of the 11 series'Power Supply:The power supply output's 12 volts DC and 1.2 ampsWhen I calculate using it says I only need 1ohm 1/4 watt resistors, I haven't tried this yet but it doesn't seem to me that this would rectify the situation. My guess was that I need 1 watt resistors, but the calculator didn't seem to agree.Any thoughts as to what my problem is? is it safe to go with 1 ohm 1/4 watt resistors? or do I need 1 watt resistors? Any help would be very appreciated, thank you!

Topic by hapticdata   |  last reply

Can any one tell me 0.218k ohms or 0.220k ohms = how many ohms and the color code of the resistor? Answered

Can any one tell me what is the color code for 0.220k or 0.218k resistor

Question by Soumojit   |  last reply

how many ohm resistor do i need to get 5v from a 9v battery? Answered

Hello i am writing up an instructable on setting up a wireless receiver , however i requires both 5v and 9v output, and the whole point of it is that it is simple and cheap, so i need to know, how many ohm resistor do i need to step down 9v down to 5v? i do not wish to use a 5v regulator unless one can be bought for less than $2, or else the instructable will cost too much.

Question by oldmanbeefjerky   |  last reply

How to calculate resistor size for lasers in parallel - for dummies

I have four laser modules taken from laser pointers. Normally each module runs off of three hearing aid batteries in series, 1.5 volts per battery 4.5 volts total. I want to run all four laser modules off of two D size batteries which are 1.5 volts each 3 volts total in series.The problem is they will not light up when connected to the two D size batteries in series ?  When I use a power supply they will light up even at only 1.5 volts  ( although dim ) up to 5.5 volts,after that they become permanently dim, with the brightest at 3 volts. It seems like I have to limit the amps not necessarily the volts. Each module has its own resistor  - the # on it is 680. When I measure the resistance it shows 68 ohms. What do I need to do to get this to work ? There must be some way to simply figure this out.... By the way I have about 40 more laser modules and I might like to use them all at once to make say..... an unquestionably visible turn signal bulb for my truck or maybe a very illuminating flood light for my backyard .... If I can figure this out the possibilities are endless !            

Question by I Need To Know   |  last reply

Help with voltage/resistor

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.

Topic by pennsteve   |  last reply

How to calculate resistance?

Ok, I need to figure out how to know what resistor to use. I know how to read a reistor, I just dont know how to use one. Say I hook an LED, a 9 volt battery, and a resistor in a circuit. I want to get the voltage down to 3 volts. How would I go about calculating a resistor reading? What ohm resistor would I use? How do I know?

Question by Adum24   |  last reply

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? 

Question by blkhawk   |  last reply

How inefficient are resistors? Answered

I know how to calculate resistive losses, but do different types of resistors have different amounts of losses (power in vs power-out, in watts) From my own observations, connecting a 10 ohm resistor across a barrey will cause significant heating in both the resistor and battery, and cause the wires to get warm. All of this is resistive loss, but when I exchange the resistor for a 10k resistor, there is virtually no heating at all. What if I use a 0 ohm resistor (direct short). The only thing getting hot would be the power supply, due to internal resistance. Does this mean higher resistance is less lossy and by definition, more efficient, or is this simply due to the fact that there is less current flow, and less power loss, and efficiency (% of power loss)  With an ideal constant current source, will the losses though any resistive load be equal? ( X amount of watts lost/dissipated @ 1A) Is it possible to limit current like a resistor without losses? (I know PWM techniques are more efficient, but I want actual resistance rather than chopping current flow and filtering with an inductor/capacitor RC filter)

Question by -max-   |  last reply

What is a 1/4 watt resistor? Answered

Alright, So I know the basics about resistors and what-not, but as I was buying beginner supplies, I noticed there were resistors in OHMs and Watts, What's the difference between the two? And like, can the unit Watt be transfered into OHMs? And which one would I use when my general area of working would be around basic LED work and noob stuff like that xD?

Question by E D E N   |  last reply

Are resistors need with mosfet?

I posted a very similar topic a couple minutes ago but I'm pretty sure noone can see it, so I'm copying and pasting the body. I just want to check this before I blow up my mosfet (I've never used mosfets before) Is it correct that you don't have a resistor from the voltage source to the gate (unlike bipolar transistors) Should or shouldn't you have a 1M ohm from gate to ground? Let's say I'm driving a mosfet from a 555, should I have a resistor from the output pin to gate? I think the schematic I'm reading just through a mosfet in where a bipolar use to be without changing that resistor.

Topic by guyfrom7up 

What it does? Answered

HI, i have a circuit  in the image above this is a simple led circuit but i found a resistor between positive and negetive terminal  the resistor's value is 15 kilo ohms but i don't know what it does in this circuit can anybody tell me ( Elaborate! ). regards Samad Haque

Question by ubdussamad   |  last reply

how many ohms does this resistor have in the led


Topic by dereklevine158   |  last reply

step down voltage with a resistor?

Hey i used a 1 mega ohm resistor instead of transformer before bridge recifier and it works the led glow but the glow of led is very much less why???

Question by taylorsane 

Arduino, Multiplexing, LED's and Resistors.

Ok ok. I'm rather new to electronics, had very minimal use with resistors. I could probably work out which resistor I needed for a series LED connection, but because it's multiplexing, it stumps me on whether it is a series or parallel connection. Pretty much, I'm wanting to run a 5x5 matrix, using these leds (information on it there), through my Arduino, I know some users here have Arduino, but the factsheet, with voltage and currents information is there.I am wondering, what resistors I'm going to need to use. If you could also say how you calculated that, it would be splendid. Is multiplexing connecting LED's in series or parallel?EDIT:I noticed the led link didn't work, but they have the following specs: How bright/dim is 3mcd? I'm assuming it's pretty dim...# Luminous intensity: 3mcd# Forward voltage: 2.1V DC# Forward current: 15mA

Topic by Noodle93   |  last reply

How many volts do I need to power a white 3mm LED that has a 240 ohm 5% resistor attached to it?

 I sacrificed a string of battery powered Christmas lights hoping to be able to use the LEDs in other projects.  The whole string contains 18 LEDs, every 4th of which blinks and is powered by 4 AA batteries.    The resistors attached to the LEDs are very small and look like they have red, yellow, brown and gold bands, which is how I came up with 240 ohms, but I'm not positive I'm seeing the colors correctly.  The yellow may be white.  Is there such a thing as a 290 ohm resistor? I'm determined not to let good LEDs go to waste, but I don't want to just try random batteries and hope for the best.  I want to use the right combination to get the most life out of both the LEDs and the batteries.  Thanks in advance for your help.

Question by alwaystomboy   |  last reply

joule thief without resistor?? Answered

I want to make a joule thief,  but I don't have the 1k ohm resistor, so what can I use instead? or will it work without the resistor? Thanks for answer!

Question by aninda13   |  last reply

Can you "Daisy Chain" resistors? Answered

Can you chain together multiple resistors to add up their ohms into a larger amount.

Question by lamboboy732   |  last reply

I need help correcting impediance on speakers.

Here's some background on what I'm dealing with: I run a haunted house in Nashville TN called Devil's Dungeon. We have a sound system that is controlled from a rack with 6 2 channel power amps. 4 of them are 260W by 2 channel and 2 are 500W by 2 channel. I have 10 cd players running to a 24 channel mixing console and the way I control each room on a separate channel is by using the post-fader sends (yeah, it's a really old peavey, but the new ones don't have post -fader sends per channel) as a line out per channel. IE: i run a line directly from the post-fader send per channel to the power amp's input. Here's my problem: There are more speakers than there are outputs, and the speakers are placed where they are needed in a particular scene. It is a large building and it would be highly laborious to try and correct the impedance by putting extra speakers and with series/parallel combinations and as we are already open this season and I don't want to re-engineer the entire system. Is there any way to correct the impedance with some kind of variable resistor? Everything I've seen so far that could handle the power is pretty large, and if possible, I'd like to put it in a relatively small project box. Can this be done with a potentiometer? I only need to correct it by a few ohms and the only POT's I've seen have been in K increments .

Topic by Scurge   |  last reply

Hot, Burning Resistor Question

Ok....I have 24 leds in parralel attached to a 9 volt battery - and a 10 ohm resistor - as reccommended by - but, when i connect the circuit and hold the resistor in my hand, it becomes INCREDIBLY hot. Each led is in parallel, individually. it normal for it to be that hot, or did I do something wrong?

Topic by Joe426   |  last reply

9v to 3v "easy button" hack. Answered

Hello! Im working on a Staples Button Hack! but..... Problem that I have is that I feel like it is a Waste to scrap the original "that was easy" message. And the problem that comes along with this would be that I have to use a 9v battery to power the new circuit and the original button circuit uses a 3v battery. I'm not great with Ohms law but I do relize that I need a resistor but... i do not know if that will put in too much current into the original circuit?Would anyone know how I can calculate this? And does the amount of current even matter? -Thanks! Noobiefied

Question by noobiefied   |  last reply

Identify resistors? - well, sort of

So, i have a bunch of project that i want to do, i have schematics and the parts (but i don't know what the color bands of the needed resistors are) Can some one give me a link to a utility converting numbers (470 Ohm) into color bands (yellow, violet, brown) please help/reply! thank you!

Topic by Sandisk1duo   |  last reply

High/Low light LED switch

I recently purchase some 3528 300p LED Strip Light so that I can make some under cabinet lighting. I wanted to make my own because I believe I can to it for a much better price and learn something in the process rather than buying an LED light set from a big box retailer. I have a 3 position rocker switch Off/high/low. If possible I would like to use the LED lights in a High/Low configuration. From what I read they make PWM modules that control the LED making them appear to be dimmable, but I do not want to use one of these devices. For the low setting I was considering wiring in a POT or an inline resistor to drop the Voltage to the LED's. On second thought I suspect that this would not work and if I drop the voltage too low this would result in inoperable LED's. By the way I would not be opposed using an inline resistor if this is a good way to reduce the light level Is there some cheap electronic component that will produce or simulate an approximate 50% PWM that I can wire inline with the switch, in effect producing a low lighting mode? I am not interested in using a variable PWM control, I just want to achieve a switchable high/low lighting. I am not familiar with components and I hope you could suggest a few ideas for my project. Some details: The led strip will be ~11 linear ft using 12VDC and about 40W of electricity.

Question by baudeagle   |  last reply

2 ohm 1/2 watt 5% Resistor - Replacement

I'm trying to find what 2 resistors I could use in parallel to replace a single 2 ohm 1/2 watt 5% resistor. E24 series. Red/Black/Gold/Gold Thanks,

Question by Howard_S   |  last reply

Why does this work, and is it doing anything at all? Answered

Take a look at the pic, i have a 9v battery, two 50 volt 3300uF capacitors, and a 2.4 volt green 20ma led, when i hook up led normally i need a resistor and proper powr supply, but i was bored and started randomly hooking things together(mad science) any way i hooked the 2 capacitors together and wired a led inbetween them, plugged in the 9volt and the led started dim then got brighter then i have ever seen these crappy leds get, i left it on for 30 mins and it stayed on, i expected a fast burn out due to no resistor but no it was great, then i unplugged the 9v and the led slowly faded off which i kinda guessed would happen dimmed for 10 seconds then turned off.. ok my Q why did this happen, i have little expierence with capacitors, know they make good tazer but thats about it. and why did the led work like this with no resistor? is the capacitor pulling enough power that the 9v is working on lower volt? w/e answers please

Question by dougiedougworld   |  last reply

why are the resistors heating up?

So i have 48 UV LEDS and each has a 470 ohm resistor on the anode so in a sense all leds are connected in parallel but it has a resistor on it. when i connect my 12 volt battery with 6500 MA the resistors begin to heat up. is there anyway to prevent them from heating up? or what is it that im doing wrong. ill provide a picture on the way the leds and resistors are connected if you want me to but hopefully what i said gives you an idea on how they are connected.

Question by diabloboy   |  last reply