Alt-BEAM Archive

Message #09675



To: beam@sgiblab.sgi.com
From: cactus@dynamite.com.au
Date: Tue, 1 Feb 100 05:24:24 GMT
Subject: [alt-beam] Sim D1 notes and questions


Hi, I'm Simon and I'm in Canberra, Australia. I've been lurking on the list
for a month or two now but have only just started trying to build things.

I breadboarded a SIM D1 yesterday. I had no end of trouble trying to get it to
trigger and spent a lot of time trying to work out why the voltage at the input
of the inverter stayed high when I covered the solar cell, until I realised
that even with my hand pressed over it, the sunceram was still putting out more
than half of it's nominal voltage. Once I put the circuit inside a dark
cupboard and closed the door, it triggered perfectly.

Experimenting after dark, I found that even turning on a 60W desk lamp two
rooms away and around a corner was enough to prevent the SIMD1 triggering or to
make it switch off.

Watching the charge on the cap (0.16F - actually two 1/3 gold caps in
serieswith a 10000 uF cap in parallel), I found that the solar cell would
charge it to over 5 volts in daylight but as it got dark most of this charge
would drop away. Moving the circuit to a dimly lit room, I could watch the
charge drop by about 0.01V/second. In just a few minutes the charge had
stabilised at 2.15V (the solar cell output in the dim light), which was not
sufficient to drive the circuit I wanted to drive (a piezo chirper requiring a
minimum of about 2.7V).

I haven't had a chance to check yet but I think the power is bleeding through
the hex inverter (it's an HC so it shouldn't use up too much). Removing the
multimeter didn't seem to slow down the rate of leakage, so I don't think it
was the meter eating up the juice.

Any thoughts on how I can conserve the voltage in the cap even as the light
dims in the evening and still have it there when the SIM D1 triggers?

Thanks,
Simon.

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