Alt-BEAM Archive
Message #03177
To: beam@corp.sgi.com
From: Steven Bolt sbolt@xs4all.nl
Date: Tue, 11 May 1999 08:18:45 +0200 (CEST)
Subject: [alt-beam] Re: SMD SE
On Mon, 10 May 1999 Bumper314@aol.com wrote:
> Well, I would like to tell you guys that from the advice given to me from
> Dave, they both now work great in the sun, What I did was added a 15 ohm
> resistor in parallel with the coil. Thanks Dave
If you trigger at for instance 2.5V, and your driver is any good,
you'll be wasting an initial 150mA through that resistor!
On Mon, 10 May 1999 Bumper314@aol.com wrote:
> > Wouldn't it be more elegant to trigger a monostable, instead of a
> > latch with an off-level? That way you get a timed pulse, and reset
> > would be achieved if the voltage dropped enough to unset the 1381,
> > instead of all the way to 0.7V or so.
> So are you trying to sport you SE designs here =). Well if you can get them
> to fit on a 3/4 cm^2 PCB then i will consider it.
SunEater_V fits easily on 2.7x3.5cm. Very enthousiastic,
tinyPager-motored `bot.
But if you have easy access to a nice choice of 1381s, why not use
them. 1381 output connects to the active high input of a monostable
(1/2 74HC221, for instance). A 100N cap and a resistor - somewhat
less than 1M for best pulse, I imagine - determine the output
timing. 1K connects a BC817-25 to the active high output. The
transistor drives your coil and there you probably are. The
smallest supercap (47000uF) would provide sufficient current in a
light and compact package, and the voltage would hardly drop
between pulses.
That's five and a half components for a single SE, or eleven for a
double version. The 74HC221, all resistors, the 100N cap and the
driver are SMT. Your 1381 will seem rather large...
Best,
Steve
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# sbolt@xs4all.nl # Steven Bolt # popular science monthly KIJK #
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