Stokes’ ProjBlog

A journal documenting innumerable, mostly terminally in-progress undertakings. Nerdiness abounds.


‘The Motor Controller Project’ September 3, 2007

Filed under: New project!,The Motor Controller Project — Stokes @ 10:41 pm

This project is actually sort of a sub-project; it will later be used to drive more interesting things.

This is my first attempt at an L298 H-Bridge motor driver board. It is based primarily on some sample schematics from the L298 data sheet; some inspiration was also gleaned from other similar projects available on-line. This will also be my first attempt at etching a PC board, which is a little daunting.

The design is fairly straightforward; it isn’t much more than a breakout board for the L298, plus the minimal handful of additional parts to support it. I’m going deliberately simple in order to keep it as generic as possible; I originally bought my L298 ICs with the intention of providing forward and reverse for a pair of standard DC motors, but it now looks like my first application will be driving a bipolar stepper motor.

L298 H-Bridge board schematicL298 H-Bridge board schematic

The nonpolarized capacitors are .1μF (-20/+80%) 25V ceramic discs; the polarized one is a 1000μF 35V electrolytic. The diodes are 1N5404 (3A, 400V) — ignore the fact that they are labeled 4004 in the schematic. I’m only planning to run at most 12V motors, so these values are probably overkill. Better safe than sorry — and aflame.

I’m moderately happy with the layout, except the zig-zagging needed to accomodate the diodes. It looks kind of cool, but is more complex than I would like, especially for my first etched board. I could have adjusted the length of the diode’s leads on the top of the board, but EAGLE does not seem to be able to do that (or at least thoroughly obscures how to do it). I’m going to try to fix my Fink installation (which I sort-of broke, trying to port some other apps ‘by hand’) and use gEDA from now on. Ignore the top-layer pads (the red rings) around the diodes and capacitors; those are just ‘notes’ to myself. Since I’m going to etch this myself, I’m free to misuse symbols to my heart’s content.

I picked up a standard-width industrial-grade Sharpietm marker at the local stationery store and placed an order for an ultra-fine one. Everything I’ve seen suggests that these are exactly what electronics catalogs sell as a ‘etch-resist pen’ for several times the price. The advertising text on the barrel states that the pen “remains permanent under most chemical washes”. I’m going to do some practice etching on scrap first, so I’ll put the pen through its paces at the same time.


1 Comment for this post

mattk Says:

w/r/t Fink: You might want to try MacPorts (formerly DarwinPorts) at instead. They have most of what Fink does, but they’re much more actively maintained.

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