If you’ve worked on a project with small LEDs, you know the frustration of determining their polarity. This ingenious LED Probe from [David] packs a lot of useful features into a simple, easy-to-implement circuit.
Most multimeters have a diode test function that can be used to check LEDs; however, this goes a step further. Not only will the probe light up an LED, it will light up no matter which side of the LED the leads are touching. A Red/Green LED on the probe will indicate if the probe tip is on the anode or cathode.
The probe is powered by a single CR2032 battery, and you may notice there’s no on/off switch. That’s because the probe enters a very low-current sleep mode between uses. The testing intelligence is handled by either an ATtiny85 or, in the newest version, an ATtiny202, though the basic concept and design are compatible with several other chips. All the design files for the PCB, the ATtiny code, a parts list, and a detailed explanation of how it works are available on [David]’s site, so be sure to check them out. Once you build one of these probes, you’ll want something to test it on, so explore some of the LED projects we’ve featured in the past.
Clever, and I believe it can work for any LED, providing it´s not a COB LED array where several LEDs are put in series. So, not good for LED light “bulbs”
For under $20 you can get a LED tester (look for TV back light tester) that’ll test anything from IR LEDs @ 1.2v up to 300v. Not sure why so high when TV back lights are usually around 100v. Eh.
Current limited from around 1mA to 25mA. There’s a bunch of different versions with slight different limits and functionality. Go buy one, they’re quite handy.
In my case I just took these: https://vi.aliexpress.com/item/1005007524074093.html, removed the leads and jammed a couple of batteries in it to make these: https://www.kickstarter.com/projects/toney/ledtwee-tweezers-for-led.
Good enough for most LEDs but doesn’t do auto-polarity so don’t forget to colour one side red. Could always adapt this idea and add indicator LEDs for polarity.
Great ideas 👍
The tweezers are the hardest part.
Wouldn’t you want a small resistor, in addition to the battery to avoid the damaging the LEDs?
Nah, coin batteries don’t put out enough current. Lots of torches drive LEDs at 6v (2 x lithium coin cells), they last forever.
I can’t actually remember what I used, was either something like 3 x LR44 or similar size lithium (eg 927). Made it yeas ago and have never had to change the batteries.
Pure series with shorting on failure is best, I have one big light panel (TV) that is in the mid to high 200 hundred volts. The testers at $20 should be a substitute driver for these big light panels the best light source for work ever.
Thinking about it, LED bulbs in 240v countries probably run at about 200v. Maybe more.
It may depend on the bulb type. I have done modifications to LED flame bulbs and the LEDs themselves don’t run more than 3-9vDC despite taking in 120v AC. There is a transformer circuit that you can bypass and run the LED matrix straight off a DC source. IIRC the transformer block was rated for 80-250vAC, but it has been a few years so my memory may be hazy.
Most of the LED bulbs I’d played with were about 70v.
Out of curiosity I knocked the top off a bulb and tried the tester out. 288v. Huh, well, that explains it.
Each LED runs at 36v (so 12 LEDs internally) and they’re in a string of 8. Aldi Starke bulbs, for anyone interested.
And of course I can’t see properly, them there things are bright.
I guess it would depend on the density of the LEDs and what type they are. The Flame Flicker bulbs are 30-40 LEDs or somewhere around there. They don’t need to be high output, which would explain their voltage usage. You are rarely seeing every LED firing at 100% output in that example.
A multimeter with a transistor hfe test socket is handy for led testing. High efficiency leds light when connected between E-B. Led cathode as emitter (NPN). Old and low efficiency leds only light between E-C.
OK, that’s actually a hack.
A aa battery with pogo pins and a 3d printing parts and a simple 0.9v to 5v boost circuit plus a resistor to limited the current to ma . You can make a simple one from the left over components. https://x.com/lu_honghong/status/1453802030347259908?t=3N9LhzRR_zsIVdw8hnnCwg&s=19
Something went wrong, but don’t fret — let’s give it another shot.
⚠️ Firefox’s Enhanced Tracking Protection (Strict Mode) is known to cause issues on x.com
Haha, sure X, sure, you go ahead and wait to see when I’ll give it another shot.