Photo-transistor floating baseline removal?
Photo-transistor floating baseline removal?
(OP)
I am trying to design an analog trigger using a photo-transistor. I started by placing the sensor in a Wheatstone bridge to get a zero volt baseline. This works great if the lighting conditions don't change. However, the lighting does change and the baseline moves.
I attempted to use op amps in a proportional feedback loop to stabilize the baseline to no avail. Essentially, I need the circuit to act as a high pass filter with a stable, zero volt baseline.
My questions: Are there any basic solutions to stabilize this base line using op amps? Is a Wheatstone bridge a good idea in this scenario? Should I consider a different approach?
Thanks
I attempted to use op amps in a proportional feedback loop to stabilize the baseline to no avail. Essentially, I need the circuit to act as a high pass filter with a stable, zero volt baseline.
My questions: Are there any basic solutions to stabilize this base line using op amps? Is a Wheatstone bridge a good idea in this scenario? Should I consider a different approach?
Thanks





RE: Photo-transistor floating baseline removal?
Another approach would be to find a schematic diagram that matches your requirement. It's not likely that anyone anywhere could find a new and unique application for phototransistors.
RE: Photo-transistor floating baseline removal?
I have never heard of the method you are attempting because any ambient light change or temperature change will mess things up.
You usually want a fairly fast average to compare with the instantaneous to generate a pulse.
What are you trying to do?
Keith Cress
kcress - http://www.flaminsystems.com
RE: Photo-transistor floating baseline removal?
itsmoked: I am creating an outdoor camera trigger.
RE: Photo-transistor floating baseline removal?
Add a base-emitter resistor, to drain the stored charge (from the photons) off the base of the phototransistor.
Mike Halloran
Pembroke Pines, FL, USA
RE: Photo-transistor floating baseline removal?
RE: Photo-transistor floating baseline removal?
Mike Halloran
Pembroke Pines, FL, USA
RE: Photo-transistor floating baseline removal?
RE: Photo-transistor floating baseline removal?
RE: Photo-transistor floating baseline removal?
http://www.analogzone.com/avt_0829.pdf
www.MaguffinMicrowave.com
Maguffin Microwave wireless design consulting