high pass filter

[gis]

Hi,

I am trying to build a circuit for detecting a visible light source (such as
red LED). I am using a phototransistor, and want to filter out all ambient
light (cieling lights, etc..)... anyone know how to construct a High Pass
filter to do this? say cut out the 60 hz room lights

pgs

 

[Gene]

You must power the LED with a relatively high frequency (1-10Khz), so
that you can extract from the phototransistor signal the frequency
component belonging to the light originated by the LED and reject all
the spurious components (60, 120, etc. Hz). For this you need a bandpass
filter. You must also make sure that the spurious light impinging on the
phototransistor doesn't saturate its output.
Gene