Re: scavenging opto-isolators

Allan Adler <ara@xxxxxxxxxxxxxxxxxxxx> writes:

As for the opto-isolators, each pair consists of a transparent piece,
which I think is the transmitter and which I will denote TR, and a black
opaque piece, which I think is the receiver, and which I'll denote BL.
Both pieces seem to have exactly the same shape, to wit:
(1) Both have three leads descending from the device. The leads are in
a row, but the middle one seems to be bent to point in the direction
that the light travels. So, they sit on the PCB as tripods.
(2) The device itself looks like a television set. It is roughly cubical.
The bottom has the leads coming out of it. One of the faces not in
the plane of the leads has a nearly inscribed disk which is slightly
recessed. In appearance it is like the TV screen. On the face opposite
that one is a kind of bulge, reminiscent of the bulge at the back of
many TV sets. On this device it looks like the top of an LED.
[snip]
Now, suppose I am looking at the face of TR containing the bulge and I
see the three leads below it. Labeling the three leads 1,2,3 is not very
insightful into the function of TR. What would be a more insightful labeling?
Likewise, if I am looking at the disk of BL and I see the three leads
below it, what would be an insightful labeling of the leads?

After several attempts, I tried searching for
3-pin infrared emitter led
and eventually found
http://www.robots-dreams.com/2005/01/controlling_you.html
It looks reasonably like my devices. The pins on it are, from left to right,
output, gnd, vcc. I'm not sure I can assume the pins have the same meaning
on both TR and BL.

The following occurred to me, but might be nonsense: Maybe the fact that TR
is transparent and BL is black is partly irrelevant. In other words, maybe
both are essentially the same device, with a bulge that emits and a recessed
disk that receives. Maybe TR is a lousy receiver and a good transmitter, while
for BL it is the other way around, for reasons having to do with one being
transparent and the other not. Taking a wild guess, the output pin is the
signal received by the recessed disk. On a device that receives badly, the
output should be very low and it might be safe to tie it to ground. That might
be consistent with the way some pins are tied together on the two opto-coupler
pairs. And it would also imply that the pins have the same meaning on both TR
and BL.

Anyway, that is just speculation. I'll keep looking for data sheets. I'm
also trying to find books on these optical devices.
--
Ignorantly,
Allan Adler <ara@xxxxxxxxxxxxxxxxxxxx>
* Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and
* comments do not reflect in any way on MIT. Also, I am nowhere near Boston.
.

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