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
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
You can use a optical filter in front of the sensor. Or you can use an RGB sensor and software to detect a specific light frequency. Just depends what your are really looking for.
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