with 74*245 motor drive
This was my first-ever walker circuit, so I
wanted to start with something that had been used
before. As a starting point, I used Wilf Rigter's
This circuit is pretty simple (no reverse, no
turning, only 2 chips), so it was just what I
needed for this project. A number of other folks
had touted the use of 74*245
chips for motor drivers, so I changed Wilf's
circuit in that direction. It turns out this (like
many things in life) had been done before -- here
is a fairly "traditional" circuit layout:
While this layout is simple to build on a
breadboard, it's a mess if you build
your own PCBs, as I do (a number of jumpers are
required). I modified the traditional layout to
come up with a simpler PCB
design (look, Ma, no jumpers!):
Essentially all I did was to re-route the path
that the quadcore
takes through the 74*14
chip -- rather than running down one side of the
chip, then down the other, in my layout it
"zig-zags" from side to side. I wound up building
this circuit in a ".1" and ".2" variant; the ".2"
version has provisions for (i.e., sockets for)
filtering capacitors on chip power lines, the ".1"
doesn't. Note that you can avoid the clutter of
these capacitors if you buy IC sockets with power
filtering capacitors built in (tho' these sockets
cost about $2 US each, vs. a few cents for "plain"
the life-size PCB
"artwork" for the Walker 2:14:1.2 circuit.
A higher-res (x4) version is available
I make the PCB
via the "Press-N-Peel"
method, and can repeatably produce these
cards without much trouble.
Here are pictures of the top and bottom
of a populated Walker 2:14:1.1 PCB,
on a 1/4" grid.
Here's how to lay out the components on a Walker
Here, the D1 diodes are small (optional)
indicator LEDs, D2 diodes are small-signal diodes
(1N4148, or equiv.), C2 are (optional) filter
capacitors (I use 0.22 uF), C1 are the quadcore
timing capacitors, R1 are the quadcore
timing resistors, and R2 are current-limiting
resistors (1 KOhms) for the LEDs. Note that the
filter capacitors (C2) always face consistent
polarity power, so you can use polarized capacitors
for them if you like; the timing capacitors (C1)
see varying polarities as a normal part of
function, and so must be monolithic non-polar
The values for C1 and R1 determine the neuron
firing times, and so are functions of the gear
motors you use and the voltage you're running this
circuit at. I use Mac floppy eject motors (which
are efficient, if a bit slow) and run the circuit
at 5V, and find that C1 = 0.22 uF and R1 = 2.2 MOhm
works well for me. Your mileage may vary.
Note that the 74*14
ICs are "socketed," both to protect the ICs
during soldering, and to allow for experimentation
subfamily. Similarly, the timing resistors and
filter capacitors are plugged into individual
sockets to allow for tinkering.
As is mentioned elsewhere,
the 8-pin DIP
socket allows a variety of "brain" cards to be
swapped on and off a given walker.
For more information...
You can think of this circuit in two parts --
quadcore and driver. The 74*14
circuit is explained here;
while the 74*245
driver circuit is explained here.
Andrew Miller used to have a site up with a
walker tutorial; his tutorial was adopted by Bram
Van Zolen here
when Andrew shut down his site. Andrew's tutorial
is educational, but pretty font-intensive. Less
"busy" versions are here
Note that Andrew's tutorial is based around an
earlier version of a 74*14
driver (essentially an older variant of the
2:14:1 circuit, with manual PNC
Chiu-Yuan Fang's "Miller" walker tutorial is
he also has another 2-motor geometry here.
For a taste of the possibilities, you should
check out Ian Bernstein's "BEAM-Online" megagallery
of walkers here,
and the BEAM
Bestiary pages on walkers here.
If you're new to Nv
nets and such, I'd recommend you check out the
material at BEAM
From the Ground Up.