2019-05-24 IR Slave Flash


I had an old RCA TV with an early remote control that used an IR beam with different frequencies for 6 different functions. I also had a VCR with the newer remote that sent the codes digitally over a 38kHz carrier. I built a remote extender so I could use both remotes beyond their short range. The problem was the remotes were totally different, so I made the extender so it was just a preamp, amp and output so whatever came in was what it sent out to the IR LED 20 feet away, and it worked well with both remotes. What went in was essentially what came out.

I thought this same method would be a good way to make an IR slave flash. An IR phototransistor is pointed at the camera’s IR LEDs. This has to have an opaque cylinder around it to keep out any ambient light. The input to the preamp is coupled by capacitors so that only the sharp risetime of the flash is zmplified. The timing of the flash is not important because the amplifier and driver puts out power only for some tens of milliseconds, long enough to illuminate the photo. The current pulse through the output driver transistor and IR LEDs is very high, at least an amp.

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