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From: John Popelish
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X-Mailer: Mozilla 4.7 [en] (Win98; U)
Subject: Re: Ultraviolet sensor?
Date: Thu, 17 Oct 2002 03:26:19 GMT
NNTP-Posting-Date: Wed, 16 Oct 2002 23:26:19 EDT
Richard Haendel wrote:
> "John Popelish" wrote in message
> > LEDs make pretty good photo detectors with high cut off energies. A
> > green one should detect down to violet, and a blue one should detect
> > only ultraviolet. You would have to have access to a calibrated
> > tunable source ot quantify the output, however. But it would be
> > pretty easy to calibrate it compared roughly with sunlight.
> How do you connect a LED for use as an input device instead of an output
Just like any other photo diode. You can amplify the voltage it
produces (photo voltaic mode) or the current it produces while an
amplifier forces its voltage to zero or holds a reverse voltage across
I think you should first try the zero volt mode by connecting it to
the - input of an opamp, with a high value resistor (1 to 10 meg ohms)
between output and - and the other side of the diode and the + input
to ground. This forces all the diode current to appear across the
feedback resistor, while the opamp provides a signal source to your
There is an example at the bottom of page 6 (current ot voltage
and a much deeper dive into the subject:
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