Datasheet for some eBay "generic" IR LED's ?  - Page 1
Forum section: electronics / beginners

author: onesixright
author_rank: Frequent Contributor
timestamp: October 16, 2017, 01:26:16 pm
content: Hi All,Anybody a clue what to use as a "basic" datasheet for some IR leds from ebay? I bought a few:- IR infrared LED 940nm Lamp High Power- IR infrared LED 940nm Lamp Black ReceivingThe seller wrote "generic" FWIW. I tried to look for "940nm IR LED", but not a clue where to go ...Thanks a bunch!

author: Coceth
author_rank: Contributor
timestamp: October 16, 2017, 03:15:37 pm
content: That is one of the trade-offs of buying parts from eBay: no datasheet, no listed manufacturer, ultimately no responsibility. Maybe they are parts taken from the same factory that produces name-brand parts, but they can't advertise the exact origin, hence the killer price.I bought a 50 pack of LEDs from eBay for $2 shipped, but I didn't expect, nor receive, a datasheet with a characteristic curve. For my little project, I didn't care, I just wanted cheap LEDs that got bright. Buying the same thing from Dig-key would have cost $10.

author: rstofer
author_rank: Super Contributor
timestamp: October 16, 2017, 06:06:14 pm
content: IR LEDs are a little harder to work with because the light isn't visible. I can't simply change resistors until I get the amount of light I want.Except... I can look at the IR LED with a cell phone camera and get some idea about how it works.Here's some data on a generic IR LED: Vf=1.5V at 50 mA. So, given a 5V power supply, calculate the series resistor as (5.0 - 1.5) / 0.05 or 70 Ohms. Maybe start at 100 Ohms and work down.https://www.sparkfun.com/products/9349But that for THIS LED, not yours. You will need to experiment. Start at 5V 470 Ohms and work down until you see the knee in the graph when you finally get to Vf. There's a discussion here but it includes superfluous detail at the semiconductor level:http://www.phys.uconn.edu/~hamilton/phys258/N/led.pdf

author: Twoflower
author_rank: Frequent Contributor
timestamp: October 16, 2017, 07:09:47 pm
content: Careful with the camera approach. It might work well. But some cameras have very good IR-cut off filters included. For example the iPhone 4S main cam has a very effective filter. I killed 2 IR-LEDs before I actually checked how well the camera detects IR-light. Try with a IR remote control the capability to detect IR emission.You could also try to slowly increase the voltage and detect the steep part of the current/voltage curve. That's probably the best operating point.

author: onesixright
author_rank: Frequent Contributor
timestamp: October 17, 2017, 07:04:45 am
content: Quote from: Twoflower on October 16, 2017, 07:09:47 pmYeah I already noticed. Same with my iPhone 6. However if you dim the lights and you look very (and I mean very) carefully, you can see a bit of purple-ish light being emitted. But, its very hard to see. Funny since some remotes being shown very well on the iPhone, different wavelengths?

author: rstofer
author_rank: Super Contributor
timestamp: October 17, 2017, 04:43:48 pm
content: Maybe try a DSLR camera?

author: Twoflower
author_rank: Frequent Contributor
timestamp: October 17, 2017, 05:25:03 pm
content: Yes, that different visibility might be wavelength related.Just try the secondary, front facing cam. At least on my iP4S the IR visibility was much better.

author: onesixright
author_rank: Frequent Contributor
timestamp: October 17, 2017, 07:14:55 pm
content: Quote from: rstofer on October 17, 2017, 04:43:48 pmNot much lucky with my Canon, but it works much better with my old Logitech 2Mp webcam

author: onesixright
author_rank: Frequent Contributor
timestamp: October 17, 2017, 07:17:40 pm
content: Quote from: Twoflower on October 17, 2017, 05:25:03 pmGood tip, just tested it!On my iPhone 6, itsmuch(and I mean much) brighter with the front face camera then the "better" rear camera...