help needed driving a bipolar stepper motor with dual H-bridge

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hi everyone,

I'm currently working on a stepper driver for a bipolar stepper as decribed at I'm using several stepper motors from scanners/printers and a L293D dual H-bridge in the two control wire setup.
It seemed to be working today, however the torque was very low. A discontinuity in the breadboard I later discovered caused the 12v psu not to be connected. The motor was probably running on the 5v logic supply. When I did connect the power supply to pin V2, I instantly fried the L293D (Although i finally got some real action, this was not exactly what i hoped for).
I checked the wiring with the scheme, replaced the l293d and reconnected the psu, resulting in another plume of smoke rising from my desk. I must be doing something wrong, can anyone help?


(here's a video of one of the steppers at work: )

It's all about the current. Most likely the current drawn by your motors at 12V is much higher than an L293 can handle. You need a motor driver rated for higher currents, and you need to know what the current draw for your motors is before properly sizing a motor driver.

You can also deliver a smaller amount of effective power to your motors using PWM (the analogWrite() function) on the motor enable signals. But if you want torque, there is no substitute for an appropriate amount of high current.

If you can tell us the part numbers of your motors or otherwise measure the current draw of your motors at 12V (can you hook them up to a power supply that reads out current?) then perhaps we can suggest a more appropriate driver than the L293.

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

Hi Ruggedciruits, thanks for the advise. I couldn't find the motors specifcations on the internet, however the part numbers are below.

I did find a 10ohm and 40ohm mark on two of the motors. Does this mean that at a 12v potential the current through the motors would be (I = U/R = 12/10 =) 1,2A and 0,3A? the l293d should be able to cope with at least the 0,3A current ( Can I regulate the current by adding additonal resistors parallel to the psu circuit?


- epoch t13196ah (40ohm)
- mitsumi M42SP-6TG LF ( 55829 10ohm)
- OKI (EM-546   7X27AN2)

Yes, for a 10ohm motor and 12V source you would be pushing 1.2A per phase, 2.4A total through the motor. Way too much for an L293.

The L293 should be OK with 0.3A per phase, but will likely get quite warm.

I would not regulate the current by adding resistors. Use PWM as I suggested in my previous post to deliver lower effective power.

The Rugged Motor Driver: two H-bridges, more power than an L298, fully protected

allright thanks,

I think I have to do some research on the forum then. Am I right this is done by applying two other PWM outputs from the adruino to the enable pins on the l293, putting a lower voltage on the enable pins, so that the l293d only lets part of the current through?
Can I also use a l298 hbridge, which is able to cope with 4A current?

cheers, tim


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