I'm looking to use an infrared LED and photodiode as a simple switch, i.e. turn the LED on and across the room the some other device turns on.

I've read around the subject and there are some devices that need a 38kHz signal to for the receiver to respond but I cam across this deivce - http://www.soselectronic.com/a_info/resource/d/sfh203.pdf - that would seem to be a simple photo diode.

Questions are:

• can that device work with out a 38kHz signal?
• what would be a good circuit for switching based on that device?
• are there any disadvantages (I assume the 38kHz is there to filer out environmental "noise" from other IR sources)?

 

It depends on how much reliability you desire.

A simple IR LED and IR sensor will work but not very reliable.
The next step is to drive the IR LED at 38kHz and use the appropriate IR detector.

TV/VCR remote controllers use this scheme as well as they send digital data which can be checked for data corruption.

 

Well, I figured it would work with the right circuit. As for reliability, it's not that critical in as much as the remote device either comes on or I need to send the IR pulse again. As long as it works most of the time it's not really an issue.

Any thoughts on a circuit? One solution I'm thinking about is using the IR photodiode to control the base of a suitably biased transistor.

 

You can use most common photodiodes or phototransistors for your circuit.

You will likely need a visible light filter (dark red) to avoid triggering from ambient light.