Alt-BEAM Archive
Message #13841
To: alt-beam@egroups.com
From: Ken Hill hardlock@cdsnet.net
Date: Tue, 25 Apr 2000 13:08:56 -0700
Subject: 555 & 139 = easy photobot!
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What do you get when you combine the "brain" of a Cybug and a Z-bridge
motor driver w/ reversing? Don't know exactly, but it works VERY WELL and
is VERY easy; even for a newbie like me. See the circuit for the brains at:
http://members.home.net/cybug/Cybugs/brains1.htm
It's just a 555 (use 1 for each side). I plan to use a 556 (dual 555) for
the completed bot.
The remainder of the circuit is simply a stacked pair of 74ACT139's as
described in the BEAM - Robotics - Tek papers called a Z-bridge (is the
Bushbo link down now???) :
http://people.ne.mediaone.net/bushbo/beam/motors.html
See the attached (z-bridge.gif) for the 139's pinout useage. Unless you
are using pager motors, stack 2 of them together! Trust me!
The chip is 2 separate devices and can be thought of as split down the
middle. One side for each motor. Put 47k resistors from all inputs (and
enables if used) to ground as Mark suggests in the paper.
I realized that used as a z-bridge as documented, the A0 and A1 inputs
needed to be reversed to reverse the motor! If I could do that I wouldn't
need a reverser :)
I only had a single pulsed signal to deal with from the 555. By using the
# 2 and 3 outputs instead of the # 1 and 2 outputs, (see truth table) on
the 139, I was able to connect the signal input to A1 and use A0 for
reverse from a tactile switch to V+. Want it to be timed reverse? Too
easy! Just add a 22uf cap to ground from the A0 pin. Runs backward for
about a second or so with that value - experiment!
The cybug brain is very photo active. Used as designed, it has large
pulses in the dark and shorter ones in bright light. With the right
resistance from the LDR, a very bright light will halt the output so the
bridge sends both highs to the motors, stopping them. (am I right on
this?) My plan is to have it boogie around till it finds the brightest
light then take a nap and charge it's batteries.
Both motors run at the same time at various speeds based on the light
difference between them. The reverse function will allow it to turn on a
spot, or both backup at once if both switches contact at the same time.
Why didn't I just make a Cybug you ask? Two reasons, 1) I didn't have any
L293's and 2) I didn't like the added circuitry for the reverser and
voltage regulator used on it. I'm powering my bot with 4 AA nicads (about
5 vts) which shouldn't be too hard to solar charge. Anyone know how to
make a 1381 trigger when the voltage drops to a certain level?
13842 Wed, 26 Apr 2000 02:12:20 -0000 What is going on, email list wise... alt-beam@egroups.com "Jean auBois" In case you hadn't heard elsewhere...
>From: aubois@trail.com
>To: jaf60@s...
>Date: Tue Apr 25 19:10:23 2000
>Subject: alt-beam vs. beam on egroups.com
Mark Dalton isn't working for SGI anymore; as a result, SGI isn't
supporting the BEAM emailing list. As a result of that, mail isn't
being forwarded to alt-beam.
However, Mark has started a replacement list on eGroups called beam
to which you can subscribe. Unfortunately, stuff on one list at
eGroups can't be forwarded to another one there.
So... just join egroups and then subscribe to beam and set it up to
send you individual messages or digests or (if you wish) read it on
the web. Future messages will be saved on the beam list directly,
more-or-less as was done for alt-beam. In the mean time, alt-beam
will be preserved for reference purposes.
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