Alt-BEAM Archive
Message #04336
To: beam@sgiblab.sgi.com
From: Bob Shannon bshannon@tiac.net
Date: Mon, 07 Jun 1999 18:56:39 -0400
Subject: [alt-beam] Re: Wow, ever tried this...
JVernonM@aol.com wrote:
> In a message dated 6/6/99 12:45:34 PM Eastern Daylight Time,
> bshannon@tiac.net writes:
>
> >
> > Get a three terminal, NPN phototransistor. I'm using some surplus GE parts
> > (non-standard markings).
> >
> > Simply replace the 2N3904 with the phototransistor in the standard 1381 SE.
> >
> > Think about a photopopper, and now start getting rid of all the extra
> parts
> > you
> > no longer need!
> Do you mean I can plop two three terminal npn phototransistors into a
> standard photopopper and lose the photodiodes and trim pot? Definately sounds
> like BEAM minimalisim to me. What about tactile sensors? where would they
> hook up? And how would the pin out on the phototransistor compare to the
> 3904? This sounds like a jewel to me. I wanna build one! I have the
> phototransistors, I had planned on making a vore and more type deal. But,
> this idea intrigues me as well. Good job!
> Jim
Ok, its not quite that easy, but its very interesting so far...
Yes, you loose the photodiodes, but the trim pot may remain to control the bias
on the base of the phototransitors. If the bias is right, the phototransistor
will
turn itself on, and the PNP will latch it on just like a conventional SE.
Only we did not even need the 1381 this time either!
You might also want to keep the .22 uf cap on the base, to ground, or use a much
larger
value as a total light over time integrator.
Tactile sensors also connect to the base, and change the bias level. Remember
that
a 3 terminal phototransistor works just like a normal transistor until light falls
on it
and alters the net base current. By altering the bias point, you can force the
transistor on
or off.
Oh yes, the oscillation 'problem' of the 1381 SE, cannot produce it with this
photosensitive
SE, so far. But I'm becomming a beleiver in the theory that this problem is due
to too high
a base current limiter resistor value (2.2K IS too much). I've experimented with
a small trimpot
but not seen as much change in 'efficiency' as in reliability.
Still need a name for this new photosensitive SE, unless it's been done before and
already
has some obscure name I'm unaware of. Any hints from the lesser gods?
------------------------------------------------------------------------
eGroups.com home: http://www.egroups.com/group/alt-beam
http://www.egroups.com
- Simplifying group communications
Home