I know that Sharp and Radio Shack make units which automatically decode IR signals (i.e. IS1U60L, GPU152X, etc.), but I need to roll one of my own using an external phototransistor.
I'm a rookie engineer, so bear with me.
I'm thinking that the phototransistor receives a signal, which is then amplified using a darlington-connected NPN. DC current is filtered out next (maybe with a capacitor in series). The signal is then fed through a 40-kHz active bandpass filter which will reject noise and environmental effects. The filtered signal is then fed through a bridge rectifier and a capacitor to convert the 40-kHz modulated pulses to DC. Finally, the output is fed through a Schmitt trigger to smooth out the waveform.
Does this sound right?