Bi-Polar Stepper Drive with L293B (help needed)

Hi folks!

I'm about to print a PCB for a motor drive, based on the "/Reference/StepperBipolarCircuit" schematics, from the Arduino website (can't post links yet).

I'm using a L293 B instead of the D, so I've included 8 diodes as shown below:

As a begginer in electronics I would like to clarify some point before actually designing the PCB (and doing something stupid!! :D)...
Even without the images, any suggestions about the questions 2 and 3... any help will be most welcome!

1-First, and most important, did I put the rectifiers in the right place?
2-Are all those groundings common, or I need completely separated logic(5V)/motor(12V) power supplies?
3-Are the 1N4007s and the 2N2222s ok for this setup?
The alternatives I have right now are 1N4148s and 2N3904s...

Basically the drive will be used with small steppers scavenged from printers and optical drives, nothing above 1A.

Thanks in advance,
Rodrigo Fonyat

Ok, now the images...

The reference circuit:

And my version:

Rectifiers look like they're in the right place.

I would separate the logic and motor supplies physically, but electrically they have to be the same.

1N4007 and 2N2222's are fine.

1N4148's are "small signal" diodes and probably not as good for this application. 2N3904's will be fine too; any general-purpose NPN transistor will work fine.

The Quick Shield: breakout all 28 pins to quick-connect terminals

Thanks a lot for the quick reply!!!
Already working on the PCB layout... I'm posting the CAD file after finished and tested, it may be usefull to someone else.
I'll try to include a paralleled socket for a second IC, if more current is needed.

Hi folks!

After some work with a perfurated board I came up with a nice and clean layout, that should make the wiring really easy... so I'll stick to the perfboard for a while and put the PCB printing on the hold.

Anyway, I have some pictures to share and a few more questions, if you guys don't mind.

As it was built on a 10x15 holes matrix, you can put two of them on a standard proto-shield.

The pictures:

As suggested on the Top view picture (full board), is it possible to switch from using the 2 circuits saparately, to having them working in parallel?
A logical circuit with the functions set through jumpers or a dip-switch.

I'm I asking too much for a newbie?!?! hehehe...
I'm sure it would be a great feature to be able to choose between control more motors or have more current output to just one...
...but I don't have much of a clue on where to start my research!

...but I don't have much of a clue on where to start my research!

The best place to start (aside from going back to university and getting a degree in electronics ;)) is to start with the datasheet and application notes.

Buried in last paragraph of the later is this little nugget.

To accommodate motors with a phase current as great
as 3.5 A, replace the single dual-bridge IC with two devices
configured in parallel (input to input, enable to
enable, etc) to form a single bridge. It's extremely important
that you pair the half bridges – 1 with 4 and 2
with 3 – to ensure optimum current sharing.

but I don't have much of a clue on where to start my research

Start off here.

Hey, thanks Mike. That is the clearest and most concise overview of motor control I've seen yet (and I've been reading a lot about this lately). I particularly like how you deal with snubber circuits and decoupling.

Wow.. excellent reading (way more than a start). Thanks a lot, Tim and Mike.
Now I have no excuses, must get the controller working next weekend... :slight_smile:
Mike, your website is really a gift to a beginner like me, perfect balance between theory and implementation!


I'm back with some nice results this time (finally): the controller is working fine, tested with a few small motors ranging from 5V-24V, pushing up to 1A with no signs of major heating (or smoke :))...

Now, as I intend to put two identical circuits on the same shield, I'm working on this switching circuit to be able to choose the way the 2 circuits will work:

  • Normal mode (independent circuits)
  • Parallel mode (sets the 2 L293B in parallel)

After lots of research and thinking, I came up to the conclusion that all I really need is this setup (scary obvious and simple):

NOTE: all the supressed connections and references can be visualized on the driver schematics (below)

I wonder if this will work, making sure the transistors connected to the outputs of the L293B (pins 11 and 14) can handle up to 1A (better 1.5A).
To switch the input lines (pins 10 and 15) I intend to use the 2N3906.
PLEASE, correct me if I'm wrong!

And here is the driver:

Rodrigo Fonyat