Help me reverse-engineer an obsolete IR receiver?

[cvanc]

Please see attached schematic.

In the upper left corner is an input for the IR receiver.  The receiver assembly has been lost and I need to build a replacement.  This is all vintage 1983 or so.

Photos show the handheld remote and interface box (which I have) and the IR receiver on a long pigtail (which I don't have).  The schematic is for the interface box.

I'm thinking a simple optotransistor should work, but I'm open to suggestions.  Thanks.

[Renate]

I would normally have thought this would take one of those little IR photodiodes with a built-in 38 kHz demodulator.
But since there is only 12V and input (no ground) I'm thinking that it must be a bare photodiode or photo transistor.
Just try using a photodiode, cathode to the 12V.
Use your remote point blank.
You can work on improving sensitivity later.

[floobydust]

The IR input is oddball with no pullup/pulldown and it does not show a GND connection. Just two wires, +12V and IN?
With that a photo-transistor (or anything) would not work, nothing to take the 4093 input low.
And it would have low gain, not decent range with a photo-transistor, and 5V would have been enough no need to have a boost converter to 12V. The receiver module must have a pre-amp.

With the remote, if you can measure the carrier frequency or the chipset it uses.

[Renate]

Yeah, it is strange that they jump through the hoop of the DC converter for the 12 V.
For such a (relatively) high voltage I presume that a reverse-biased photodiode plays a part.
The lack of a ground is strange.
What is the jack for the receiver? Does that have the ground.
The question is whether there is a 38kHz (or other frequency) demodulator built into the pickup.
Since we are looking as stone-age stuff, I would think that they don't deal with data as fast as the raw carrier.

I have a little protoboard and software on my PC to decode IR streams.

[cvanc]

What is the jack for the receiver? Does that have the ground.

Here you go...

[Renate]

I guess that must be a 3 conductor coaxial connector.
They seem pretty cavalier about using a painted chassis for ground.

I've used a bunch of IR receiver/demodulators, something like this: http://www.vishay.com/doc?82459

The original version was probably all discrete.

You've got the remote, put a scope across the output LED and see what the carrier frequency is.

You could probably tear apart your families VCR, add a 7805 and make it work.

[floobydust]

In the early 80's Siemens was king for IR photodiodes, like SFH205 and you would use a transimpedance amp and some filtering, AGC- all of which was a big hassle. It was Telefunken, then Siemens, now Osram that makes them. This was likely inside the missing original receiver.

I would first try a vanilla consumer IR module supplied quiet 5V from that 12V. The original receiver module must have gotten GND from the connector housing.

I wonder if the IR receiver does not demodulate because of U1211, U1209 seem to be a synchronous demodulator divided down off the 5V serial data clock. Hard to know the serial data rate at J1201, if it is super fast then Vishay TSMP58000 is a receiver module with the raw carrier output 20-60kHz.

[Renate]

That is a wacky circuit.
All the 5V that powers everything (including the 12V DC converter) is being fed in J1201 with a superimposed processor clock for the 8085A!