Alt-BEAM Archive

Message #12563



To: beam@sgiblab.sgi.com
From: Bruce Robinson Bruce_Robinson@telus.net
Date: Sun, 26 Mar 2000 12:54:52 -0800
Subject: [alt-beam] Re: 2nd post - Anyone please? - Reverser circuit drawn wrong??


Ken Hill wrote:
>
> Regarding the 240 reverser circuit from the beam online site,
> If appears that from the data sheet of the chip that the number
> 2 inputs and outputs should actually be reversed on the drawing?
> Those two bottom buffers run the other direction across the
> chip don't they?

I believe you're right, Ken.

> ... Or should they just be moved up one pin on the chip?

You could do that as well. As shown (assuming you swap the In2 and Out2
labels), each motor is reversed independently. If you move the bottom
two connections up, then both motors would be reversed together, which
probably isn't what you want.

> Using 2 opposite facing LEDs across each of the outputs, I can't
> get it to work that way on the breadboard. (either as drawn, or > reversed).

The circuit is meant to drive a logic input (virtually no current). If
you try to drive any kind of a load, even a small LED, those 47k
resistors will drop the voltage to just about nil. You can verify that
it's working as expected by using a second '240 temporarily to drive
your LED's.

> Also, I found the circuit for the 245 H bridge and the 139
> reverser / H bridge circuit. If I use the 139 I can eliminate
> both the 240 reverser and the 245 H bridge, correct?

The combination of the 74HC139 and H-bridge (one chip'll drive two
bridges) can replace the '240 reverser plus '245 driver. If you're going
to go this route, use the complete schematic shown in the Tilden paper
... the BEAM on-line H-bridge has positive logic and the '139 outputs
will fry it. If you have very low current motors, you can do it all with
just a '240 using the BEAM-online schematic.

Bruce



12564 Sun, 26 Mar 2000 14:58:02 -0600 [alt-beam] Re: 2 new bots beam@sgiblab.sgi.com SG At 11:38 PM 3/25/00 -0800, you wrote:
>That's ONE next step. There are lots more.
>
>In each case, you need only modify
>the head ... the robot will follow.

yup, i myself was thinking of a bot that looks for its charger.
the charger would let out beeps (beyond human hearing freq.) and thats what
the walker would go to.
hooking itself up might be an interesting task. Dosn't the cybug do
something like this?
-Sparky

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