You've probably read that photo-transistors are slow to respond to an input signal. Try it sometime, setup a 555 to drive an IR-LED at about 1kHz and a 1k resistor in series with the transistor. If you are quick enough, you could count one Mississippi, two Mississippi...

OK, not really. Still, the transistor I grabbed needs help. Let's try a cascode, but not just any cascode, a folded cascode. Why this configuration? It will operate nicely on the 3.3V supply used by the microcontroller and provide a logic level signal to the processor.

This is the circuit

as it stands today, though I still twiddle with it from time to time. A pending change is to use a 2N5087 in place of the A733. In the past, when I had 20m of cable between the circuit and dev board, there was an emitter follower on the output. (This was just a quick sketch, I should have checked annotations.)