I build a lot of guitar effect pedals. All LED’s for a 9V battery get a 4.7K limiting resistor. Preserves battery life and still plenty bright, especially on a dark stage. Great video! Thank you.
@Dean Joe i really appreciate your reply. I got to the site thru google and im in the hacking process now. Seems to take quite some time so I will get back to you later when my account password hopefully is recovered.
I can't thank you enough for all your videos. They are simple and informative. I am not an electronics engineer but I had theoretical lessons in electronics. I learned more with your videos than with my lessons. Thank you very very much
Always good to see a back to basics video. I look forward to them because you have a way of explaining things that we're all expected to know but nobody spells out.
Searched for help in this LED delimma and this video answered all my questions. Great Tips Had not thought to use VOM to verify Amps load. trying to use LEDs at a trigger for motion detection in a model train. Now I need a sensitive Light detector to fire a relay. Thanks so Much, Dennis
Great tutorial for unknown generic LED's. I think a 10 turn 1k ohm pot would be a quick way to find the ideal brightness & current then measure the pot and go up or down to the nearest off the shelf resistor value. Seems like 10 to 15 mA is the sweet spot for longevity vs brightness. trade off. Thanks!
WOW another informative video you have taught me so much about led's and ohm's law i have begun to put leds on all my RC planes ty and keep me learning 👍
So many people feel really disappointed when they find out just how approximate science can be. To make things even worse you'll find few suppliers stock resistors, capacitors or anything else with values in increments of "1". I suspect that's partly why Paul collects meters and oscilloscopes and not calculators. You expend all your degree calculating your resistor to 8 decimal places only to find the supplier only stocks the "e-series" of values so ball park numbers are the best you can do. To make it worse that's ballpark +/- a couple of k.
This video is really informative: I didn't imagine it was so simple to setup LEDs. I just knew the rule of thumb of 220Ohm current limiting resistor....LOL
Great explanation and demonstration, just wish you would have shown the wiring hookup thru the breadboard, meter and decade box in detail. Can't see what wires are going where.
"If you're new to electronics and need the info". Pshaw I have been wiring LEDs since the 80s as a pre-teen. Still, I needed to figure out the forward voltage of an unknown and couldnt quite work out how! Good vid.
on my 8 bit CPU I use 270's on all the LEDs so running around 10mA. I think most of them are the GaAs and GaP chemistry type (old style), there are a few (2, one is in a bicolour LED and the other a modern diffused type) blue LEDs in there but still plenty bright enough running with a 270R
Hi, guy - enjoyed the little tutorial. You didn't mention how to address putting multiple LEDs in a string - I'm kinda assuming that you just add all their forward voltages together. I'm building a UV exposure box for PCB fabrication, and have obtained some 3 watt, 365nm UV LEDS to be used as the light source. They have some pretty funky characteristics - as follows: Emitting Colour: UV DC Forward Voltage: 3.9V - 4.5V DC Forward Current: 700mA Luminous Intensity: 50~55mW Wave Length: 365nm - 370nm Viewing Angle: 120 Degree Power:3w Voltage:3-3.4V Current:700mA Color:UV Wavelength:365nm~370nm Lifespan:50000h That 700mA forward current kinda caught my eye. I'm planning on running 4 strings of LEDs, with 5 LEDs on each string. If I run them at 4.2 volts per LED, then each string should want about 21 volts, with no resistors in the mix at all. The current requirement would be 700mA * 5, or 3.5 amps per string; with 4 strings, I'd be looking for a power supply that could crank out 14 amps at 21 volts, for a total of 294 watts. Hell, that can't be right. The LEDs are rated at 3 watts; 20 of them should draw 60 watts, not 294. Nuts. Feel free to jump in anytime, now. I'd hate to screw this up; these 365nm LEDs (the frequency specified for Riston) are bloody expensive - around a couple bucks each. Your comments would be welcome - thanks, Charlie ADDENDUM I guess the current requirement is not additive - each string of 5 LEDs wants just 700mA, so I need a power supply that can crank out 21 volts at 2.8 amps, for a total of 58.8 watts. That looks better. Your thoughts would still be appreciated. If I use a power supply rated at 21 volts and 100 watts - I have one on hand - will I need resistors? I wouldn't think so... right? >Charlie
I guess this one? ua-cam.com/video/mKCAxwjfs0I/v-deo.html Still worried about the current draw. If I feed the LEDs the correct voltage, do i need to worry about their drawing to much current? >Charlie
Thank You for the info ... Needed an extra Multimeter to keep at a remote location so just purchased a UNI-T UT61E after seeing your post and reviewing it online :-)
@@charlesmarlin6632 it's not a bad multimeter. Mine was slightly off on the voltage when it came in. There is a blue pot inside you can adjust (ever so slightly) after it warms up. Again pretty decent multimeter!
There are many smd leds which are standard 3v forward voltage But can take 60mA ( 2835) to 150mA ( 5730) and so on.. How to tell their characters if they are unmarked? Here, you are assuming a max 20mA current..which is standard for these kinds leds..
Your method clearly works, but, it's a bit complicated & it uses a gadget that most beginners won't have (i.e. your changeable resistor circuit card). It's easier to put the LED in series with an ammeter & a standard resistor (e.g. 1K Ω *) & use a bench power supply (which is quite inexpensive to get these days) to gradually increase the voltage from 0 to the LED brightness level that you prefer. As you slowly increase the V with a fixed resistor in the circuit, the current level will increase in the series circuit. If you stop at the brightness level that you prefer & read the A on your meter, that will be your desired current through the LED. Then put that A reading into the original equation (that you showed in your vid) & input whatever supply V that you want to use & then compute the resistance to determine the resistor that you will need in your circuit. If you increase the V too fast & the LED fails, then you know your LED can't handle that much current--so on your next experiement attempt, go more slowly. Another interesting fact about driving a LED is that as you increase the brightness, it will reach a current level that won't increase the brightness very much more by adding additional current to the LED. Beyond that limit, you're just over-driving the semi-conductor materials & risking premature LED failure. Once you know the max brightness A before the LED will fail, a good rule of thumb is to take 70% of that current level as your driving current level for your LED (e.g.: If the LED reaches max brightness without being over driving at say 26 mA then 26 ma * .7 = 18.2 mA would be your ideal LED driving current to optimize brightness & LED longevity in your circuit. * Note: for those who may not know, the symbol Ω = Ohms (aka the Greek Omega symbol). One last final note. You could also use no resister if you have a decent power supply to determine the max brightness & current of an unknown LED, but you'd have be careful or blow a few LEDs while experimenting. You'd obviously have to start at 0V & gradually increase the voltage until you reach the desired max brightness of the LED.
@@learnelectronics True, but that isn't the alternative method that I described above. No biggie.. Just wanted to show another method that I think is easier.
Way too complicated.... Take an unknown LED, place your multimeter in current mode and place it in series with a variable power supply (PS) Set your PS to 1.5v and note if the LED is drawing any current gradually turn up the PS to ~2v the led should begin to glow and current will be drawn. If not reset the PS to 1.5v and reverse the leads to the LED. Do not exceed 2v until you see a current draw. Gradually increase the voltage until you get a current draw of 10-20ma. Congrats! You now know 2 things 1. The correct polarity of the LED 2. its voltage rating. Knowing these two items you can now use ohms law to calculate the resistor value for ANY voltage. For example suppose you have a 9v supply and the LED consumes 2.1v @ 15ma by simple ohms law (R=V/I) since we know the LED will use 2.1v we subtract that from the supply voltage of 9v (9 - 2.1 = 6.9v) this means the resistor needs to suck up 6.9v and since we know the LED requires 15ma. Using ohms law we can calculate the resistor value by V/I. In this case V will be the voltage the resistor will use 6.9v and the current (I) will be that of the LED draw (0.015A) (I is ALWAYS in amps) so we have 6.9v / 0.015a = 460 ohms. Of course that resistor does not exist so using ohms law for current or I we will use (V/R) Plug in a standard resistor value that wont exceed 15ma. Try these formulas foe ANY supply voltage to power the LED. I have hundreds of LEDs and the method he uses of identifying cathode or anode will not work as some of these LEDs you cant see into. Also remomder that some LEDs can be infrared as well! So you will not see any illumination from the LED unless you point it at your camera of your cell phone to see it glow. My way is foolproof and been using it for decades
Your timing is about 24h too late. I just sacrificed about a half dozen rando-LEDs yesterday, trying to get the less bright ones to glow like the others :-D
I enjoyed seeing your video. Very sorry to hear of your heart issue. Have you been to see a cardiologist? It sounds like you might be a candidate for a heart transplant.
I build a lot of guitar effect pedals. All LED’s for a 9V battery get a 4.7K limiting resistor. Preserves battery life and still plenty bright, especially on a dark stage. Great video! Thank you.
@Kyle Wesson instablaster :)
@Dean Joe i really appreciate your reply. I got to the site thru google and im in the hacking process now.
Seems to take quite some time so I will get back to you later when my account password hopefully is recovered.
@Dean Joe it did the trick and I now got access to my account again. Im so happy!
Thank you so much, you saved my ass!
@Kyle Wesson you are welcome xD
I can't thank you enough for all your videos. They are simple and informative. I am not an electronics engineer but I had theoretical lessons in electronics. I learned more with your videos than with my lessons. Thank you very very much
Great video Paul. Another way to identify the cathode lead is to look at the LED from above and you will see that the cathode side has a flat profile.
Always good to see a back to basics video. I look forward to them because you have a way of explaining things that we're all expected to know but nobody spells out.
Wonderfully simple. You have saved me buying at least another million LEDs. Mamy thanks.
Searched for help in this LED delimma and this video answered all my questions. Great Tips Had not thought to use VOM to verify Amps load. trying to use LEDs at a trigger for motion detection in a model train. Now I need a sensitive Light detector to fire a relay. Thanks so Much, Dennis
that was a good video Paul, its good the get back to basics, & your circuits yous should know vid's are awesome... 2 thumbs up...
Exactly the video i was searching for!
Our teacher gave us the task to find out about this exact subject, and its due to tomorrow. So thanks a lot 🙏
Thanks Paul... I always look forward to your “back to basics” videos 👌
Feel for you buddy my brother passed 2 years ago from same great outlook you have keep it up!!
Another great video Paul, I wish I would have known this when I was a kid I exploded countless salvaged leds from stuff I tookapart as a kid...
Have finally sent for a resistor board as they look really useful.
Great tutorial for unknown generic LED's. I think a 10 turn 1k ohm pot would be a quick way to find the ideal brightness & current then measure the pot and go up or down to the nearest off the shelf resistor value. Seems like 10 to 15 mA is the sweet spot for longevity vs brightness. trade off. Thanks!
Really well done, easy to understand video about a common problem in hobby electronics. Thanks!
WOW another informative video you have taught me so much about led's and ohm's law i have begun to put leds on all my RC planes ty and keep me learning 👍
You're the man Paul! I swear every question I have, you have a video to answer
Excellent video. I have learned something today. Lifesaving video to many LEDs I see coming to me in the near future. 😎
So many people feel really disappointed when they find out just how approximate science can be. To make things even worse you'll find few suppliers stock resistors, capacitors or anything else with values in increments of "1". I suspect that's partly why Paul collects meters and oscilloscopes and not calculators. You expend all your degree calculating your resistor to 8 decimal places only to find the supplier only stocks the "e-series" of values so ball park numbers are the best you can do. To make it worse that's ballpark +/- a couple of k.
This video is really informative: I didn't imagine it was so simple to setup LEDs. I just knew the rule of thumb of 220Ohm current limiting resistor....LOL
Great explanation and demonstration, just wish you would have shown the wiring hookup thru the breadboard, meter and decade box in detail. Can't see what wires are going where.
LED can be used as a Voltage Reference like a ZENER diode . Used that trick many times.
"If you're new to electronics and need the info". Pshaw I have been wiring LEDs since the 80s as a pre-teen. Still, I needed to figure out the forward voltage of an unknown and couldnt quite work out how! Good vid.
I really enjoy these basics videos, great work Paul.
1:58 "It will never blip again" Moment of silence for those gone too soon 😂
As always another great little tutorial. Keep up the great work.
perfect for a greenhorn like me! thanks!
Very fine, thanks Paul!!!
Very useful video Paul! Thank you.
Thank You!
Great lesson Paul! I remember killing a few LEDs when I started, lol
Technically Vf is the recommended voltage without really shortening the life of the LED. They can use voltages below Vf, just will be dimmer.
It could be helpfull to mention that you should convert your Miliamps to Amps for the maths exercise
Great video, dude! Thanks a lot! 😊
Another great explanation!
Simple, but important, so thanks :)
on my 8 bit CPU I use 270's on all the LEDs so running around 10mA. I think most of them are the GaAs and GaP chemistry type (old style), there are a few (2, one is in a bicolour LED and the other a modern diffused type) blue LEDs in there but still plenty bright enough running with a 270R
great video paul
Hi, guy - enjoyed the little tutorial. You didn't mention how to address putting multiple LEDs in a string - I'm kinda assuming that you just add all their forward voltages together. I'm building a UV exposure box for PCB fabrication, and have obtained some 3 watt, 365nm UV LEDS to be used as the light source. They have some pretty funky characteristics - as follows:
Emitting Colour: UV
DC Forward Voltage: 3.9V - 4.5V
DC Forward Current: 700mA
Luminous Intensity: 50~55mW
Wave Length: 365nm - 370nm
Viewing Angle: 120 Degree
Power:3w
Voltage:3-3.4V
Current:700mA
Color:UV
Wavelength:365nm~370nm
Lifespan:50000h
That 700mA forward current kinda caught my eye. I'm planning on running 4 strings of LEDs, with 5 LEDs on each string. If I run them at 4.2 volts per LED, then each string should want about 21 volts, with no resistors in the mix at all. The current requirement would be 700mA * 5, or 3.5 amps per string; with 4 strings, I'd be looking for a power supply that could crank out 14 amps at 21 volts, for a total of 294 watts.
Hell, that can't be right. The LEDs are rated at 3 watts; 20 of them should draw 60 watts, not 294.
Nuts. Feel free to jump in anytime, now. I'd hate to screw this up; these 365nm LEDs (the frequency specified for Riston) are bloody expensive - around a couple bucks each. Your comments would be welcome - thanks, Charlie
ADDENDUM
I guess the current requirement is not additive - each string of 5 LEDs wants just 700mA, so I need a power supply that can crank out 21 volts at 2.8 amps, for a total of 58.8 watts. That looks better. Your thoughts would still be appreciated. If I use a power supply rated at 21 volts and 100 watts - I have one on hand - will I need resistors? I wouldn't think so... right? >Charlie
Look for my video, leds in series and parallel
I guess this one? ua-cam.com/video/mKCAxwjfs0I/v-deo.html
Still worried about the current draw. If I feed the LEDs the correct voltage, do i need to worry about their drawing to much current? >Charlie
thank you paul very interesting love it great fun
What is that you are using to change resistance value?
Your multimeter looks alot like the. UNI-T UN61E amazing!
Thank You for the info ... Needed an extra Multimeter to keep at a remote location so just purchased a UNI-T UT61E after seeing your post and reviewing it online :-)
@@charlesmarlin6632 it's not a bad multimeter. Mine was slightly off on the voltage when it came in. There is a blue pot inside you can adjust (ever so slightly) after it warms up. Again pretty decent multimeter!
There are many smd leds which are standard 3v forward voltage
But can take 60mA ( 2835) to 150mA ( 5730) and so on..
How to tell their characters if they are unmarked?
Here, you are assuming a max 20mA current..which is standard for these kinds leds..
Simple, when the LED burns then it was the kill you Ohms resistor ;) - love it 👍
I found it. Thanks
Hey, awesome video, thank you. Can you provide the link to the resistor board. I think that could be pretty handy. Thank you.
www.ebay.com/itm/Seven-Decade-1R-9999999R-Programmable-Resistor-Board-Step-1R-1-1-2-W-PrR-Sqi4/373197924796?hash=item56e45469bc:g:YXgAAOSwHgRbpL05
One LED was Sacrificed to the Electric Gods....
my dude is out of breath just sitting talking about LEDs 🤣
How about 12v LED?
Great tutorial. I always appreciate learning first principles. I am curious, what is the source of your decade resistor board? Thanks, Kennedy
Ebay
@@learnelectronics , please, do you get the name of the ebay-shop , please ..
@@blackfaithdoom9018 www.ebay.com/itm/Seven-Decade-1R-9999999R-Programmable-Resistor-Board-Step-1R-1-1-2-W-PrR-Sqi4/373197924796?hash=item56e45469bc:g:YXgAAOSwHgRbpL05
Cool.
Also all of these types of LED's have a FLAT on the lower portion of the body that is used to indicate the cathode also.
I just measure Vf of an unknown LED, then use the formula.
Where can I get resistor board like that?
Banggood, aliexpress, Amazon
Artur m.banggood.com/200V-1R-9999999R-Seven-Decade-Programmable-Adjustable-SMD-Resistor-Slide-Resistor-Board-Step-Modul-p-1386475.html?rmmds=search
As they where I come from "MY MAN!"
Your method clearly works, but, it's a bit complicated & it uses a gadget that most beginners won't have (i.e. your changeable resistor circuit card). It's easier to put the LED in series with an ammeter & a standard resistor (e.g. 1K Ω *) & use a bench power supply (which is quite inexpensive to get these days) to gradually increase the voltage from 0 to the LED brightness level that you prefer. As you slowly increase the V with a fixed resistor in the circuit, the current level will increase in the series circuit. If you stop at the brightness level that you prefer & read the A on your meter, that will be your desired current through the LED. Then put that A reading into the original equation (that you showed in your vid) & input whatever supply V that you want to use & then compute the resistance to determine the resistor that you will need in your circuit.
If you increase the V too fast & the LED fails, then you know your LED can't handle that much current--so on your next experiement attempt, go more slowly.
Another interesting fact about driving a LED is that as you increase the brightness, it will reach a current level that won't increase the brightness very much more by adding additional current to the LED. Beyond that limit, you're just over-driving the semi-conductor materials & risking premature LED failure. Once you know the max brightness A before the LED will fail, a good rule of thumb is to take 70% of that current level as your driving current level for your LED (e.g.: If the LED reaches max brightness without being over driving at say 26 mA then 26 ma * .7 = 18.2 mA would be your ideal LED driving current to optimize brightness & LED longevity in your circuit.
* Note: for those who may not know, the symbol Ω = Ohms (aka the Greek Omega symbol).
One last final note. You could also use no resister if you have a decent power supply to determine the max brightness & current of an unknown LED, but you'd have be careful or blow a few LEDs while experimenting. You'd obviously have to start at 0V & gradually increase the voltage until you reach the desired max brightness of the LED.
I said at the outset of the video you can use standard resistors.
@@learnelectronics True, but that isn't the alternative method that I described above.
No biggie.. Just wanted to show another method that I think is easier.
I just measure Vf of an unknown diode, then use the formula. That is easy.
Watch out for those killy ohms lol
Where do i get that "variable resistor board" or decadebox as you called it ?
www.ebay.com/itm/Seven-Decade-1R-9999999R-Programmable-Resistor-Board-Step-1R-1-1-2-W-PrR-Sqi4/373197924796?hash=item56e45469bc:g:YXgAAOSwHgRbpL05
Way too complicated....
Take an unknown LED, place your multimeter in current mode and place it in series with a variable power supply (PS) Set your PS to 1.5v and note if the LED is drawing any current gradually turn up the PS to ~2v the led should begin to glow and current will be drawn. If not reset the PS to 1.5v and reverse the leads to the LED. Do not exceed 2v until you see a current draw. Gradually increase the voltage until you get a current draw of 10-20ma.
Congrats! You now know 2 things
1. The correct polarity of the LED
2. its voltage rating.
Knowing these two items you can now use ohms law to calculate the resistor value for ANY voltage.
For example suppose you have a 9v supply and the LED consumes 2.1v @ 15ma by simple ohms law (R=V/I) since we know the LED will use 2.1v we subtract that from the supply voltage of 9v
(9 - 2.1 = 6.9v) this means the resistor needs to suck up 6.9v and since we know the LED requires 15ma. Using ohms law we can calculate the resistor value by V/I. In this case V will be the voltage the resistor will use 6.9v and the current (I) will be that of the LED draw (0.015A) (I is ALWAYS in amps) so we have 6.9v / 0.015a = 460 ohms. Of course that resistor does not exist so using ohms law for current or I we will use (V/R)
Plug in a standard resistor value that wont exceed 15ma.
Try these formulas foe ANY supply voltage to power the LED.
I have hundreds of LEDs and the method he uses of identifying cathode or anode will not work as some of these LEDs you cant see into. Also remomder that some LEDs can be infrared as well! So you will not see any illumination from the LED unless you point it at your camera of your cell phone to see it glow. My way is foolproof and been using it for decades
As alway, love the video. The other benefit of low current draw is a slightly smaller electric bill. Save the planet. haha not.
Your timing is about 24h too late. I just sacrificed about a half dozen rando-LEDs yesterday, trying to get the less bright ones to glow like the others :-D
" It Will Never Blip again..." ROFL
I enjoyed seeing your video. Very sorry to hear of your heart issue. Have you been to see a cardiologist? It sounds like you might be a candidate for a heart transplant.
Yep, been in treatment for 7 years. Not quite ready for a heart job just yet.
I want that resister array!