Newsgroups: comp.robotics
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From: dabbott@atnf.CSIRO.AU (David Abbott)
Subject: Re: MicroPower robots
Message-ID: <1994Jun15.111755.26773@rp.CSIRO.AU>
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Organization: CSIRO Australia Telescope.
References: <2tectp$9t5@handler.Eng.Sun.COM>,<2th773$npm@vixen.cso.uiuc.edu>
Date: Wed, 15 Jun 1994 11:17:55 GMT
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In article <2th773$npm@vixen.cso.uiuc.edu>, cburian@ux4.cso.uiuc.edu (Christopher J Burian) writes:
>cmcmanis@Sun.COM (Chuck McManis) writes:
>
[...]
>
>Another idea is turning on an SCR with a Zener in series with the gate.
>When Vcap-Vzener reaches .8V, zoom.  But this is just a wild guess.  I 
>have neither Zeners nor SCR's handy, or I'd breadboard it before posting.
>
>Chris Burian
>

Yup, use a crowbar circuit. I'd suggest a programable bandgap reference 
rather than a zener (eg. TL431) slightly lower leakage current, and you 
probably only need a thyristor not a SCR.

For really low leakage current use a micropower CMOS comparator to switch 
the thyristor, and compare the capacitor voltage to another capacitor
that you reacharge each time the threshold is reached, something like a 
peak detector circuit using micropower opamps. (And you'll need another
reference to allow the whole thing to start up) You were going to put a 
microcontroller in the circuit anyway weren't you ;-)

good luck,
Dave

