If you check TAOS catalog you'll find a chip that includes
photodiode(s), a preamp and an A/D converter. Some of their evaluation
boards allow you to connect to a computer via USB. Then use a Unix
machine (including *BSD, Linux, MacOS X, etc.), write a quick script
set it on cron.
Another solution is to use a chip what incorporates a photodiode, a
preamp (I/V conv) and a F/V converter. You can connect this type of
signal to an audio input and you can sample the signal that way. It
would require some signal processing (I'd rather use zero-cross
intervals instead of FFT-type spectral estimation) but it's also
pretty straightforward.
Watch out for spectral sensitivity of the photodiode, and the dynamic
range of the system. Bare silicon photodiodes are most sensitive to IR
and red. Some chips incorporate optical filter to attenuate red/IR so
that the sensitivity peaks in green region. Those are closer to human
eye sensitivity distribution. (Peak at 510nm for night vision, 550nm
for color vision.) Photodiodes respond linearly to the light
intensity, not to the logarithm of the light intensity, so it may be a
bit tricky to cover the entire range without physical attenuator.
Received on 07/04/06-03:38:52 PM Z
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