Alt-BEAM Archive
Message #03196
To: beam@corp.sgi.com
From: Steven Bolt sbolt@xs4all.nl
Date: Tue, 11 May 1999 18:34:16 +0200 (CEST)
Subject: [alt-beam] Re: SMD SE
On Tue, 11 May 1999 Bumper314@aol.com wrote:
> In a message dated 5/10/99 11:18:35 PM Pacific Daylight Time,
> sbolt@xs4all.nl writes:
>
> >If you trigger at for instance 2.5V, and your driver is any good,
> >you'll be wasting an initial 150mA through that resistor!
>
> I thought the pulse looked a little dead =), so what should i do
> then. I cant swap out the SE now, its in the middles, I can get
> to it though. Should I put a resistor in series with the solar
> cell?
If you want to stay with a switch-off level (instead of a
switch-off time), increasing that level is probably the most
efficient solution. You might try a 1N4148 diode in series with the
2K2 resistor (anode towards the 3906 base). That will make the SE
switch off at about 1V instead of less than 0.8V. Check if the
level is high enough to allow a restart without that resistor over
the coil. If not, add another diode.
Of course this will shorten the pulse to the coil. If it becomes
too short, you need a larger storage cap.
Note that a monostable would not merely avoid all reset trouble.
If you stop and think, you'll realize that using the storage cap
and the load as a crude RC timer isn't very good design. The
monostable gives you an independent RC constant, easily adjustable
for maximum efficiency. In this case, I imagine that the coil
accelerates something and that the pulse should end when the
maximimum speed is achieved. Use a 5mm variable resistor, and fine
tuning the RC constant is no problem at all.
The monostable also allows the use of a convenient little supercap
for storage, without lengthening the charge/discharge cycle.
> > SunEater_V fits easily on 2.7x3.5cm. Very enthousiastic,
> > tinyPager-motored `bot.
> wow, is stuff up on your SunEater_V yet? I dont think i followed your
> description to well on that SE, would you mind wipping up a schematic?
All will appear on the usual Webpage, when I find the time to write
it...
> And about my 1381, I guess I didnt write that well, I actually
> made another one tonight and its only 5mm by 5mm by 2mm. not bad.
Very tiny. But it's best to first get a larger prototype to work
well, before you shrink a thing :)
Best,
Steve
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# sbolt@xs4all.nl # Steven Bolt # popular science monthly KIJK #
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