Help to identify this component - Page 1
Forum section: electronics / beginners

author: jroark
author_rank: Newbie
timestamp: September 16, 2015, 08:14:14 am
content: I picked up a box of miscellaneous components and there was a bag of what I thought were LEDs but they aren't. They have no markings except a number 1-7.They seem to be sensitive to light. When I expose them to bright light (nearly touching a light bulb) they generate ~1.5v?

author: continuo
author_rank: Frequent Contributor
timestamp: September 16, 2015, 09:42:30 am
content: Photodiodes? Or Infrared LEDs?

author: bktemp
author_rank: Super Contributor
timestamp: September 16, 2015, 09:50:35 am
content: Are you sure they are not LEDs? LEDs can be used as photodiodes and they look the same like those LEDs:http://www.digikey.com/product-detail/en/SSL-LX4673GD-LA20/67-1082-ND/270880

author: Cliff Matthews
author_rank: Unknown
timestamp: September 16, 2015, 10:05:36 am
content: That's one crazy motley-meter!But never trust one that needs a new battery..

author: Gyro
author_rank: Super Contributor
timestamp: September 16, 2015, 10:06:38 am
content: How have you identified that they're not LEDs?They may be older (dimmer) than modern high efficiency ones, if you're just using the Diode test setting on your DMM they may be too dim to see. Try putting 20mA through them and see if they light up then.

author: Daniel_Reyes
author_rank: Regular Contributor
timestamp: September 16, 2015, 10:23:51 am
content: Those are time-machine diodes.Sent from my SM-G900P using Tapatalk

author: Cliff Matthews
author_rank: Unknown
timestamp: September 16, 2015, 10:46:04 am
content: On further view, these puppies have round leads... My LED stock spans ~30-years and none of over 1000 pieces has round leads. It's usually cut formed metal so the cathode sits on a surface facing the top.

author: tooki
author_rank: Super Contributor
timestamp: September 16, 2015, 11:19:06 am
content: Quote from: Cliff Matthews on September 16, 2015, 10:46:04 amI've got some LEDs from the 80s that look exactly like those (except in red) and indeed have round leads. So I'd still bet my money on them being LEDs. However, their lead lengths are reversed from most LEDs, with the short lead for the anode instead of the cathode.

author: xrunner
author_rank: Super Contributor
timestamp: September 16, 2015, 12:00:31 pm
content: Well, they look like these vintage LEDs I found on the internet. I think they are LEDS.

author: Cliff Matthews
author_rank: Unknown
timestamp: September 16, 2015, 12:29:10 pm
content: My vote is LED but I submit those round leads are odd.

author: Quarlo Klobrigney
author_rank: Super Contributor
timestamp: September 16, 2015, 12:33:43 pm
content: I can verify that. They stopped using those way back in 2079.They would fail during translocation and cause all sorts of biological issues later on.Quote from: Daniel_Reyes on September 16, 2015, 10:23:51 am

author: TimFox
author_rank: Super Contributor
timestamp: September 16, 2015, 04:53:51 pm
content: An illuminated photodiode measured with a high-impedance voltmeter will read the turn-on voltage for the semiconductor junction.Since you read 1.5 V, which is typical for an LED, that implies GaAs or other Ga compound LED. Note that the device might contain a current-limiting resistor (for use on 5 V or similar), but that doesn't affect the voltage measurement.Many diode-test functions on DMMs are useful for Schottky (0.3 V) or silicon PN (0.7 V), but don't work at higher voltage, especially if there be a series resistor.

author: Quarlo Klobrigney
author_rank: Super Contributor
timestamp: September 16, 2015, 05:36:05 pm
content: Exactly Tim, I was going to rebut my humor with just that before the power went out here for 4 hours. I have a number of LEDs that run on 12V with no resistor in any lead. Like Lady GaGait was born that way. I suggest that a sacrifice of one of them is in order, to the god of hidden smoke to really find out. Start at 3-5V, switch directions, and raise the voltage, rinse & repeat. All this is assumed to have a current limiting supply or resistor in series.Quote from: TimFox on September 16, 2015, 04:53:51 pm

author: jroark
author_rank: Newbie
timestamp: September 16, 2015, 08:32:17 pm
content: Thanks for all the helpful replies (and not so helpful)I think the consensus is it's an LED. I hooked one up to my linear power supply (assumed long leg +) but got no output or current draw. I'll reverse the polarity and try again.Thanks