I know this has been covered before and the conclusion was to use a
sharp IR sensor...but! I don't need an accurate distance, I just want
a relative distance - moving closer, moving further away...
I've found this circuit which is supposedly for the Roland D-Beam
controller (a controller on a musical keyboard that senses the
distance to your hand and adjusts something accordingly).
It appears to just use an ir led and phototransistor. Is the rest of
the circuit just the correct band pass filter?
Are there any other circuits out there similar to this?
14 years ago