Cheapish multimeter that can light white LEDs - Page 1
Forum section: electronics / testgear

author: tom66
author_rank: Super Contributor
timestamp: January 25, 2016, 07:29:42 pm
content: Looking for a multimeter that'll make white LEDs glow on diode range - amongst other features, but this would be a valuable feature to have. So must have an open-circuit diode voltage of ~3V or more.What would be a reasonably cheap option? It will be used for low voltage testing only, so safety of the front end isn't a serious concern.

author: TheWelly888
author_rank: Frequent Contributor
timestamp: January 25, 2016, 07:40:55 pm
content: Problem with diode testers that has 4V+ compliance voltage is that many non-white/blue LEDs have reverse breakdown voltages of 5V or less.

author: Fungus
author_rank: Super Contributor
timestamp: January 25, 2016, 08:06:37 pm
content: You can easily make a small LED tester with acouple of CR2032sand a constant current LED driver (eg.AN6884is very flat and easy to solder, just tie the input high and you get 5 x 17mA current sinks)Just tape it to your multimeter of choice.(In fact it's will so small it might even fit inside...just bring out a couple of metal contacts or a banana socket)

author: Muxr
author_rank: Super Contributor
timestamp: January 25, 2016, 08:11:06 pm
content: Quote from: Fungus on January 25, 2016, 08:06:37 pmThanks for reminding me, I actually need to make me a little SMD pad tester for when I hand pick and place 805 LEDs. Because it can be annoying orienting them correctly. Sometimes they aren't marked.

author: retiredcaps
author_rank: Super Contributor
timestamp: January 25, 2016, 08:13:49 pm
content: This review of some multimeters has a list of the ones that can light white LEDs.http://www.robotroom.com/Multimeter-Reviews-5.htmlHis version of the DT-830B can light a white LED.The Victor VC830L is also listed and Fungus, who just posted above, did a video review of it.

author: retiredcaps
author_rank: Super Contributor
timestamp: January 25, 2016, 08:20:21 pm
content: The one in Fungus' video might be an updated version and maybe he can verify it outputs 3V in diode test mode?If yes, they are selling for less than 10 pounds on ebay and aliexpress.

author: tom66
author_rank: Super Contributor
timestamp: January 25, 2016, 08:44:14 pm
content: Quote from: TheWelly888 on January 25, 2016, 07:40:55 pmNever had a problem with any LEDs myself up to around 10-15V; I think the 5V is a guaranteed minimum. Anyway, if it is current limited to less than 1mA I can't see such reverse breakdown being destructive.Quote from: Fungus on January 25, 2016, 08:06:37 pmIt's more convenient being built into a meter, rather than having a separate widget. Currently use the coin cell trick though.This is for a friend who wants to upgrade their current cheapy Tenma multimeter, they plan to use it to test/repair LED backlights on LED-backlit LCD TVs.Quote from: retiredcaps on January 25, 2016, 08:13:49 pmWill have a look, thanks.

author: retiredcaps
author_rank: Super Contributor
timestamp: January 25, 2016, 08:51:27 pm
content: Quote from: tom66 on January 25, 2016, 08:44:14 pmWhat model Tenma does your friend have?

author: tom66
author_rank: Super Contributor
timestamp: January 25, 2016, 08:57:23 pm
content: Quote from: retiredcaps on January 25, 2016, 08:51:27 pmThink it's 72-7770

author: rob77
author_rank: Super Contributor
timestamp: January 25, 2016, 09:08:19 pm
content: Quote from: TheWelly888 on January 25, 2016, 07:40:55 pmas long as the current is limited to small value it doesn't matter... the PN junction breakdown is a reversible process - nothing wrong happens until the junction is damaged by heat produced by the flowing current.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: January 25, 2016, 09:09:47 pm
content: Are you sure the budget can handle the strain?

author: Fungus
author_rank: Super Contributor
timestamp: January 26, 2016, 01:08:01 am
content: Quote from: retiredcaps on January 25, 2016, 08:20:21 pmMine puts out 2.6V in diode test mode.But...I just tried loads of LEDs and it lit them all up, dimly. Even a 1W white LED (very dim but definitely lit up).QuoteI don't know what it would do with LEDs that are connected to other stuff, or with lots of LEDs in parallel (which you'll probably get in TV backlights).If testing LEDs was my thing and I didn't want to spend much money then I'd build a special tester with the probes from a really cheap multimeter, some sort of a battery pack and one of those LED driver chips.With a battery holder likethis oneyou could put 2 batteries on one side and fill the other side with electronics, eg. a5V DC boosterand one of thoseAN6884LED drivers for current limiting.There's also space for a power indicator LED (important!) and a decent on/offswitch(the switches on those boxes are rubbish).Even if you have to buy some probes it's still only about $5 for the whole thing (and if you've got $6 you can get somepretty probesto impress people).

author: mariush
author_rank: Super Contributor
timestamp: January 26, 2016, 02:06:11 am
content: Uni-T UT61E can measure the voltage drop on white leds but they don't light up.It's not "cheapish" but then again i guess it depends on your definition of cheap.

author: Muttley Snickers
author_rank: Unknown
timestamp: January 26, 2016, 03:28:11 am
content: Couldn't help myself just had to find out what this little bugger is capable of, lights up everything I have at hand using C & E on the HFE pin header in any mode except off and the voltage across these pins is around 3.0 volts.In either continuity mode, 200 or 2000 ohms (2000 is diode test) it only just lights up everything I threw at it and voltage is again around 3.0 volts but it will not show the voltage drop of any LED, but it does diodes.Also I think the battery is low in this meter as I haven't changed it out in years, audible continuity is down a bit so probably a battery issue.Oops, I forgot the link.https://www.eevblog.com/forum/testgear/home-depots-tool-set-$15-side-cutter-strippers-multimeter-wbatt/

author: Fungus
author_rank: Super Contributor
timestamp: January 26, 2016, 11:25:44 am
content: Quote from: Muttley Snickers on January 26, 2016, 03:28:11 amIt's supposed to "only just" light them up.It will be current limited to 0.5mA or something like that (hopefully).

author: MrSlack
author_rank: Frequent Contributor
timestamp: January 26, 2016, 02:40:48 pm
content: Here's a quick design I did for a relatively crude 0.5mA current source which can be used to test LEDs and will illuminate them:Stick your multimeter across the LED to get the voltage drop.Change the 1.2k resistor for another one if you need more or less current. Formula is R = 0.6 / I.Supply voltage isn't critical but it should in theory be at least 2-3v higher than the LED forward drop max.This shouldn't knacker any LEDs if you reverse bias them by accident but I make no guarantees there

author: zapta
author_rank: Super Contributor
timestamp: January 26, 2016, 03:05:15 pm
content: Quote from: Muxr on January 25, 2016, 08:11:06 pmFrom my experience, the cathodes is on the side of the tape that has the holes.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: January 26, 2016, 03:57:38 pm
content: Here's what I use: