Alt-BEAM Archive
Message #00726
To: beam@corp.sgi.com
From: Justin jaf60@student.canterbury.ac.nz
Date: Mon, 22 Feb 1999 01:17:19 +1300
Subject: [alt-beam] Re: It works, but I don't know how... new diagram
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The diagram attached was screwed up. My apologies. I'm going to re-post
it it's only 3K - less than many text posts here, so
please forgive me...
(Technically speaking, the fault that made the first diagram unreadable
was pretty amazingly bizarre, and didn't show up at all until I saw it
in my post via my browser... As you may have noticed if you tried to
decipher the crap, it's based on the Alf SE, which in turn, is based on
the Suneater II SE :-)
> I was attempting to set up motor drivers such that while there is a
> constant input into the inputs, the solar engine triggers the activation
> of the motor drivers (either by enabling them, or by powering them). The
> only ones I have on hand are 74HC245's nicked from a microcore (It's
> Sunday evening - the electronics shops are closed), which don't seem
> very well suited to the task at hand.
>
> Anyway, I was using an LED to indicate when the solar engine was firing,
> and during one of my rewirings, the LED ended up between the se output
> and the driver enable I was playing with.
> And everything sprang to life.
>
> I don't quite understand why the LED made all the difference (this is a
> case of orang-utan electonics :-), and am interested to find out, as the
> circuit is now _technically_ doing what I wanted it to do, but seems to
> be losing a fair bit of power to the drivers while not engaged, among
> other things (my assumption is still that I'm going about this in very
> much the wrong way).
>
> The circuit is attached. It's a bit rough and quite inconsistant (rush
> job) and doesn't detail the sensor-control circuit (I assumed this
> irrelevant at the time, however I just remembered stuff that might
> indicate otherwise. Ah well.) Hopefully it'll explain what I've done
> though.
>
> If I replace the LED with anything else (diode, photodiode, short,
> resistor, etc) it won't work. The amount of light falling on the LED
> affects things however (seems to change duration or cutoff of drive),
> which might turn out to be useful, but at the moment is not.
>
> This stuff is experimentation for a photovore BTW. Those eagle eyed list
> readers will notice that recently I've been bugging you with several
> other weird questions or problems; my electronics theory is not yet
> advanced enough for me to avoid the stupid or innefficient solutions
> when faced with a problem (But I am learning :)
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727 Sun, 21 Feb 1999 09:13:03 -0600 [alt-beam] Re: stepper motors beam Richard Piotter > > Here is a simple circuit to drive a stepper coil.
> >
> > +5v
> > ___
> > |
> > o-------.
> > | |
> > < |
> > 1K > |
> > < /
> > 470 | |<' 1N4001 or equivalent
> > o---/\/\/---o---| ,------|<-------.
> > from |\ | |
> > microcore `---o--o to coil o--o--.
> > MJ2955 |
> > or equivalent _|_
> > = Gnd
> >
>
> Why the 1K pull-up on the MJ2955 base? You seem to waste
> considerable current.
Cause I took it out of my Digital Electronics text book. I guess you can try it
without the 1K. I guess it would work. Besides, I stop any REAL thinking after
12:00 AM! (:
Richard Piotter
richfile@rconnect.com
The Richfiles Robotics & TI web page:
http://members.xoom.com/richfiles
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