If anyone has experience working with the OPT101 photodiode I am trying to make a laser sensor (650nm) and am wondering if someone could help me in designing a circuit for it so when there is no laser beam, no output voltage is present. Thanks.
I don't know the specs for your photodiode, but here's a general start.
Connect the cathode (-) of your diode to the positive voltage source. Connect a suitable resistor from the diode anode (+) to signal common. The diode is reverse-biased. Only leakage current flows with no illumination. Output (~zero volts when the diode is not illuminated) appears across the resistor. Light input makes the diode "leaky" by generating hole/electron pairs in the depletion region, so output voltage goes up as more current flows through your load resistor.
How many volts, how many ohms depends on your diode, how much light you're receiving and how fast you need to go. And the loading effects of what you're connecting to the output come into play here as well.
Gosh I miss the chalkboard!
Roby
I know how the diode works, its actually an IC with a transimpedance amp built in. I was looking for someone who knows some ambient light filtering circuits that can be used to block out most other wavelengths besides 650nm, because this laser reciever is going to be opperating in daylight.
Use some IR plastic for 650 (wideband stuff) cheap too (looks dark red) get a narrowband inteference filter 10 to 40a wide and use that before detector, pricy
Light blocking circuits? Hmmm. If you modulate the laser source at a fixed frequency (by driving it with a pulse train, or by chopping the output beam with an electro-optic modulator($$$) or mechanical chopper), then you can use any sort of bandpass filter on the received signal ... just AC coupling might be sufficient. This fails if the total received light (ambient + laser) gets strong enough to saturate your detector.
An optical bandpass filter in front of the detector solves the saturation problem. Narrow-band optical filters are available for various center frequencies and bandwidths. They are expensive and should not be used behind a light-gathering lens or mirror. This because the filter's center frequency red-shifts as the incident light angle changes from normal incidence. The narrower the bandwidth, the greater this effect, reducing the effective aperture of your receiver and lowering its sensitivity.
Red plastic is the way to go if it suffices.
Roby
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