Alt-BEAM Archive
Message #00567
To: beam@corp.sgi.com
From: Justin jaf60@student.canterbury.ac.nz
Date: Thu, 18 Feb 1999 17:11:38 +1300
Subject: [alt-beam] Re: 240-based 'reverser' query
> 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.
Ok, I'm sold. I might try to hunt some off old circuit boards first (big
hassle, but so is a mail-order that I have to twiddle my thumbs for a
week for :-)
That's something - any hints from anyone as to what sort of tech-scrap
uses these things?
> 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).
Yep, I had to feed it back (Out-1a connected to In-2a, Out-1b connected
to In-2b), then close sensor two permenantly (remove cap etc) to ground,
remove two resistors, and it worked as a motor reverser. But only one
motor reverser :-(
and I think it was still way over safe current limits with just a "TPM"
style motor (though it did go...).
> Shown below is my interpretation of the missing reverser circuit
> connections, note the changed resistor connections for R1-4.
Ah yep, so they do have to be fed back through. Pity that - it means you
can't have two independant reversers. Judging by Ian's reply, I could
get two independant reversers by using motor drivers instead of just the
240. More chips... :)
> 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.
Wheeled photovore. I want to make one that is small (preferably about
the size of the 5.5V cells from solarbotics) but with a bit more
functionality than normal. Avoiding the edge of desktops is a high
priority, and from previous experience, I think that the best way to do
this involves a single touch connection triggering a motor direction
reverse. Currently, I like the look of the Alf circuit as a starting
point (extremely efficient se and light-seeker in one package, able to
drive non-inductive loads, and able to change the direction of the bot
while the cap is still discharging (thus allowing a big cap for long
bursts of light seeking activity), and has been easily modified (on my
breadboard) to run extra applications while still light seeking). So
while it still blindly follows light, it looks like a good platform on
which to build more functionality.
>
> 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+
------------------------------------------------------------------------
eGroup home: http://www.eGroups.com/list/alt-beam
Free Web-based e-mail groups by eGroups.com
Home