Hello,

Do you have a snubber circuit on your motor?
A snubber circuit is to reduce the transients from the motor.
Take a look at this page for an example:
http://homepages.which.net/~paul.hills/Emc/Snubbers.html

This is a link from the EDUCYEPDIA on power electronics:
http://www.educypedia.be/electronics/powerelectronics.htm

Bertus

 

An enormous current spike is generated on the H-Bridge supply line at the instant of the H-Bridge switching states. Chances are these spikes are migrating to the 567. Supply line and other decoupling techniques will be in order.

 

Try adding 100uF caps between the bases of the H-Bridge transistors and GND.

 

I forgot to mention that these transition spikes are a separate issue from what Bertus posted. You may well need snubbers too.

 

Hi Bertus,

I don't have an RC snubber across the motor. I did try diodes across the 4 transistors of the H-Bridge, but that didn't help. I tried CDrive's suggestion and that did work. Thank you for the links to the snubber circuits. There were good explanations on how to calculate the RC values. Even though it now seems to work ok, do you think it would still be a good idea to include the snubber?

Allen

 

CDrive, it worked! No more erratic output - motor switches on,off, and reverses smoothly and reliably. I've learned a lot from you and Bertus. I really appreciate all your help. I don't think I could have completed this project on my own. Thank you so much.

Allen

 

Allen, you're more than welcome. It was a pleasant journey.

Chris

 

Hello,

It is always pleasant to hear that a project is finished with success.

Bertus

 

Hi Folks,
My project using the NE567's with an H-Bridge motor controller is completed and successful. A special thank you to Bertus and CDrive who stuck with me and helped me solve the problems I had. I really learned a lot from you - priceless!

I'm using the unit to remotely rotate the rabbit ears antenna that sits on top of my TV. (I don't have cable)

Here are links to photos of the finished unit, the guts, and my quick & dirty remote control. When I re-draw the schematic, I'll post that too.

http://i1138.photobucket.com/albums/n525/numberdude/SDC13733.jpg
http://i1138.photobucket.com/albums/n525/numberdude/SDC13662.jpg
http://i1138.photobucket.com/albums/n525/numberdude/SDC13711.jpg