Alt-BEAM Archive

Message #12873



To: beam@sgiblab.sgi.com
From: Richard Weait crs0274@inforamp.net
Date: Fri, 31 Mar 2000 18:26:46 -0500
Subject: [alt-beam] Re: FRED tutorial


At 11:47 AM 3/31/00 -0800, you wrote:
>On the subject of the 1381 SE, I'm playing with it with a 3 vt battery
>pack using the J version. I can get it to trigger OK, but it never
>resets. The docs I could find state something about the resistance in the
>motor eventually reseting the transisters.

Hi Ken,

The 1381 will reset when the input voltage drops below the
acceptable voltage threshold. This happens all the time
when you use a solar cell. :-) With a battery, the 1381 will
stay triggered until the battery runs down. Then it won't
trigger again.

Simulate a solar cell like this:

.---/\/\/\---> >---o--- . . .
| 1K |
| + |
----- | C
--- ---
----- ---
--- |
| |
| |
`------------> >---o--- . . .

Pretend | Main circuit . . . circuit continues
Solar Cell | Storage Capacitor

The resistor limits the amount of current coming from the
battery pack to a few milliamps. That causes a slowly rising
voltage on the main capacitor. When the voltage gets high
enough, your 1381 (not shown) triggers. That makes the motor
run, which lowers the voltage on the storage capacitor faster
than the battery raises it. The voltage drops to below the
threshold. The 1381 shuts the circuit off, and we start again.

Cheers,

Richard.

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