Introduction: L293D Motor Direction Control for Under $2.20

By Baelzabubba
About: I have been working in IT since the mid 1980's. Most of that has been database and application development. I've been working on Internet application development since the late 1980's. And, we're back in Tass…

Further to my instructable 12V NE555 PWM Controller for Under $3 I have designed and built a simple and cheap DC Motor Direction Controller that can either be used with the PWM Controller, for speed control or by itself with a 12V power supply.

I designed this DC Motor Direction Controller so that I could give direction control to DC motors that I am building into mini tools (drill, lathe, table saw, solder smoke extractor, etc.). While, I don't need direction control for all of the tools that I'm building, it IS necessary for some. Plus, who doesn't want to spin their DC motor backwards?

The overarching design principles that I've used here are:

  1. Works with my NE555 PWM Controller;
  2. Works without my NE555 PWM Controller;
  3. It's cheap;
  4. It uses minimum parts; and
  5. It works

For the direction controller to work with the NE555 PWM Controller, it will take the PWM modified power from that device and modify the polarity of the signal and push it on to the DC Motor. As I mentioned with the NE555 PWM Controller, I'm only interested in a 12V motor.

To achieve this magic, I'm using an L293D Quadruple Half-H Driver, well ... I'm using half of one. If you're interested, the L293D can manage 36V, however, as discussed in my previous instructable, the NE555 PWM Controller (as designed) will handle 18V max. So there's your upper limit.

The parts list and costing for this instructable is:

  • 1 x LM7805 Voltage Regulator ($0.40)
  • 2 x 100 nF electrolytic capacitor ($0.06)
  • 2 x 2 pin header ($0.26)
  • 1 x 1k ohm resistor ($0.01)
  • 1 x SPDT slide switch ($0.05)
  • 1 x L293D Quad Half-H Driver ($0.85)
  • 1 x 16 pin DIL ($0.35)
  • 1 x 50 x 33mm PCB ($0.14)

The prices quoted are for parts purchased from eBay that I've accumulated over some time. These prices change over time ... so caveat emptor, dude.

Step 1: The Horse Before the Cart

If you are using this with the NE555 PWM Controller, that device comes first. The reason for this is simply that if the LD293D direction controller were first, you'd be switching polarity and THEN feeding it to the NE555 PWM Controller. And that would mean that the polarity would be wrong and the NE555 PWM Controller wouldn't work when the polarity was reversed.

When designing this circuit, I made a couple of mistakes ... such as, I was feeding 12V from the NE555 PWM controller BEFORE it was square waved and feeding that into the 5V regulator. All that happened was that the NE555 PWM Controller rendered itself totally redundant. No, don't do that!

Another design fault that you will see in the scan of the PCB is that the GND connections for the L293D don't go anywhere ... I had to solder in a jumper under the board to connect to the common GND of the LM7805 to make it do anything (groan!).

The above Fritzing PCB view shows both of those problems fixed.

I have also designed in two M3 holes on either end of the L293D so that I can bolt in a piece of aluminium to act as a heat sink. Feel free to add a proper heat sink if you like (you'd like to if your L293D is getting hot). The L293D will start to get hot if you are pumping > 1.5 W into it. Under 1.5 W, free air will reduce the temperature to a safe operating range. If you are going above that, you're going to need some heat sink (and a good read of the schematic and search for advice on the interweb).

Step 2: The PCB

Attached are the copper bottom and silk screen top from my Fritzing design.

These can be printed and transferred using whatever method you prefer. Personally, I prefer laser toner transfer and an Hydrochloric Acid and Peroxide etch bath.

As this design is a minimal component design and all of the traces are extra thick (48 mil), it shouldn't be too had to place and solder by eye ... well, you should use a soldering iron rather than your eye, unless you've got heat ray eyes.

Use a non-conductive washer or non-conductive bolt when bolting the heat sink to the copper trace ...

I have now added a "schematic" to the instructable. Please be kind ... I'm not very good at schematics.

Attachments

Step 3: All Done

To connect the two boards together, I've made a pair of DuPont Male pin jumpers (male to male).

To connect the motor to the board, I've gone with a DuPont Male/4.1mm Spade connector (male to female) jumper. This way, I can easily switch the motor and or motorised device without having to worry about soldering/desoldering (such a drag).

Anyway, that's it. This is a pretty straight forward circuit and build.

Check back again later, I've ordered a couple more JT0 chucks and I'm planning a mini-lathe.

Ciao!