InfraRed Detector Mystery (but not Elementary....)

[BackEMF]

TL;DR

Found a circuit element in a drawer marked "IR detectors". Trying to confirm its identity and its pinout.

Hello!

I found this circuit element below in a drawer marked "IR detectors" (which I must have written on it myself, a long time ago...although I must admit don't remember doing so #OldAge).

First of all, I'm trying to figure out what, exactly, it is. My initial assumption was that it looks like an IC-based IR detector e.g an OPL550, basically a photodiode with added amplification and filtering.

If we label the pins left to right as 1, 2, 3, taking 1 as Ground, 2 as Vout and 3 as Vs i.e. the supply voltage, it would then work as follows: supply 5 V between Ground and Vs then the internal chip holds Vout at ~5 V until an IR signal is detected, at which point it gets pulled low. However, this doesn't seem to be the case.

Clues:

Measuring with an ohm meter shows approx 10 ohms resistance between pins 1 and 2 (using either polarity). No other two pins show any pairwise conductivity.

Weirdly, connecting an oscilloscope to pin 2, and just connecting pin 3 to Vs (with no ground), seems to give some results when I point my TV remote at it and press some buttons. But as soon as I connect a ground, it all disappears!

Any ideas how I can solve this mystery?

 

[Baluncore]

Probably a phototransistor or photodiode.
https://en.wikipedia.org/wiki/Photodiode
https://en.wikipedia.org/wiki/Photodiode#Related_devices

 

[DaveE]

Just based on the standard packaging, combined with the lack of information provided, I'm guessing it's just a photodiode optimized for long wavelengths. They really only work in near IR, like 1um or so. It really doesn't look like the thermal detectors that are common at longer wavelengths. The other choices are things like metallic sulfides (Cd, Hg) and Indium compounds. I don't recall seeing those detectors packaged in plastic like that one. Plastic isn't great at transmitting IR, you'll usually see a glass window or nothing.

Anyway, one of my lab rules (even at home) was: "if you don't know the part number, throw it out and buy something that has a datasheet." Normal electronic parts aren't that expensive.

 

[Averagesupernova]

Hooking power and ground directly to unknown pins was a wrong move. Use some current limiting resistors and fiddle with it until it makes sense.
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It looks to me that the rightmost lead hooks to nothing internally.

 

[BackEMF]

Thanks, fellow sleuths. A photodiode seems likely, although the pinout still confuses me. Perhaps a phototransistor, where the base should be left floating?

Anyway, one of my lab rules (even at home) was: "if you don't know the part number, throw it out and buy something that has a datasheet." Normal electronic parts aren't that expensive.

An excellent rule! I think I'll adopt this. This should have been my approach from the beginning, but since I can't just buy components near where I live and have them the same day, I thought I'd save time by using what I had available. Several hours of tinkering later, this was a big mistake.

 

[artis]

An excellent rule! I think I'll adopt this. This should have been my approach from the beginning, but since I can't just buy components near where I live and have them the same day, I thought I'd save time by using what I had available. Several hours of tinkering later, this was a big mistake.

A good rule is also to not throw out electronic stuff but to put it aside in a reservoir and then when there is enough of it you can either sell it to electronic scrap collectors or simply give it to a proper recycling facility.
At least that is what I do.

 

[Tom.G]

give it to a proper recycling facility.

Or better yet pass it on to a budding student/tinkerer... you know, the ones that are always curious and taking things apart.

 

[dlgoff]

It looks to me that the rightmost lead hooks to nothing internally.

That's what I thought. Looks like a simple LED.

 

[BackEMF]

I managed to get an OS-1838B IR detector, so no longer need to figure out what the mystery device is exactly. But I still want to!

I compared the output waveform of the 1838B IR detector with that of the unknown element, when they are excited with a TV remote control signal. I get the following

This is for the circuit as shown above, with the 3 pins of the unknown device numbered. Pin 1 is floating. Pin 2 is connected to the 'scope (green trace). Pin 3 is connected to +5 V.

Also shown is the output from the 1838B detector, as the yellow trace. The 1838B works by staying at an output HIGH, until a 38 kHz modulated IR signal is detected whence the output goes LOW.

This is the only setup I've found for the unknown device that seems to show anything reasonable. As you can see, it matches the output from the 1838B, albeit at a significantly lower amplitude (I've also inverted the signal from the unknown device so it is in phase with the 1838B output signal.)

Does this help anyone figure out what the device identity may be? Or has anyone any suggestions for further ways to connect the device up? I'm happy to take whatever measurement you suggest and report back.

Thanks.

 

[rbelli1]

Can you see a bond wire on the right hand pin similar to the one on the center pin? It is unclear in the picture you posted.

BoB