Infrared does not normally rank very highly on my list of things to do. Suddenly, it is at the top of thay list. Confirimg the presence of a source was easy enough, I pointed a cellphone's camera at the control box, to discover a fairly bright, but flickering, light.

Digging around parts bins and junk boxes I find a selection of both photo-transistors and photo-diodes, but which to use? The transistors out numbered the diodes by a fair margin, so transistor it is. Taking a peek inside the monitor's case revealed a PIC16 microcontroller which was driving the IR LED via a single transistor. I'm guessing that maximizing the data rate was not a great priority for the manufacturer.

The first test was simply the transistor in series with a resistor, with a pair of AA batteries to power it and an oscilloscope to see the result. Well there was a square-ish wave, but I couldn't get my analog, non-storage, scope to lock on to the signal.

Let's digitize it!