Newsgroups: sci.electronics
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Light Duration Meter
Message-ID: <1989Apr8.220650.1158@utzoo.uucp>
Organization: U of Toronto Zoology
References: <102@raider.MFEE.TN.US>
Date: Sat, 8 Apr 89 22:06:50 GMT

In article <102@raider.MFEE.TN.US> root@raider.MFEE.TN.US (Bob Reineri) writes:
>... Perhaps a solar cell, connected thru an RC network, that
>would charge up a capacitor to a given voltage, depending on the amount of
>sunlight received over the course of a day. Then I could somehow measure the 
>charge on the cap at the end of the day. Just a thought....

Capacitor leakage will probably kill you on this.  This sort of long-term
memory application is where digital circuitry is ideal.  Say a 555 set up
as a slow (say a tick every 10 minutes) oscillator, enabled by sunlight
(via a phototransistor, say), feeding an 8-bit counter.  If you want more
precision, add some more bits of counter and speed up the oscillator.
If you want to measure light intensity, not just duration, use a VCO
rather than a fixed-rate oscillator.
-- 
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