Alt-BEAM Archive
Message #00537
To: Justin jaf60@student.canterbury.ac.nz, beam beam@corp.sgi.com
From: Sean Rigter rigter@cafe.net
Date: Wed, 17 Feb 1999 09:57:30 -0800
Subject: [alt-beam] Re: 240-based 'reverser' query
Hi Justin,
74AC240 is the same low power CMOS technology as the 74HC240 but has
roughly double current ( 4x source current) capability and every 74AC
part has the same type high current buffered outputs (ie 74AC240,
74AC04,740AC86 etc)!!! (at least National, Zytrex). Try Digikey etc. The
241 is the same as the 240 but one enable input is active low and the
other active high logic. The 240 enables are both active low. Yes, 240s
can be stacked but stacking the reversing circuit is redundant (not used
as a driver). With two 240s the extra buffers can be used as drivers but
must be connected differently (partial stacking plus some freeform
jumpers)
Did you test your diagram? It won't work as a reversing motor driver but
does provide "feedback" unless I'm missing something (which happens to
me all the time).
Shown below is my interpretation of the missing reverser circuit
connections, note the changed resistor connections for R1-4.
This configuration reverses (actually inverts like a bridge) the outputs
with respect to the inputs when sensor 2 is open. but there is still a
problem with sensor 1 which disables the circuit until closed. For the
circuit to be practical, the sensor 1 circuit (stop) should be flipped
(0V/+V) over or just replaced with the PNC output. The stop function is
useful in case of tipping over. I understand you will use this in a
PHOTOVORE of some kind? Wheeled or legged? Perhaps you could provide
more details on your application. I still wonder about the person and
the original intent behind this design.
240
PIN
1 sensor 1
2 in 1 - R1a
3 out 1
4 in 2 - R2a
5 out 2
6 in 3 - R3a
7 out 3
8 in 4 - R4a
9 out 4
10 gnd
11 pin 12 - R4b
13 pin 14 - R3b
15 pin 16 - R2b
17 pin 18 - R1b
19 sensor 2
20 V+
wilf
Justin wrote:
> I decided to do that myself (gotta learn somehow :) and the resulting
> diagram is open for criticism, but I believe it's correct:
> http://www.geocities.com:80/SoHo/Lofts/1121/beam/240reverser.gif
>
> For my purposes (reverser in a photovore) I'm thinking that a 74HC240
> would seem the best choice as a) It draws (considerably?) less power to
> run, b) it will use small, low-power motors anyway and c) I er... don't
> think I can get the 74AC's here... :-)
>
> Question - Can the 240's be stacked for higher current? (My assumption
> is yes, but I thought I'd ask)
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