Need help with PIC sttepper motor controller

[rafael_cordeiro]

Hi all,
I am working in a simple project for my engineering course, but as I am not really very good at electronics, I have some sort of doubts. Hope you can help me out here, since it is a very simple project.

It is a very simple sttepper motor controller using a PIC 16F628A. When someone presses the first button it will turn in one direction, when the other is pressed it goes on the opposite way. I already tested the circuit together with the software I wrote in a simulation program. It all worked just very fine, but I have a few doubts.

**broken link removed**

1st - I´ve read in the ULN2003A datasheet that the outputs can be paralleled for higher output current (each output pin gives me 500mA, so with the three I would get 1500mA). Is this the right way to do it? Should I tie together only the outputs and not the inputs?

2nd - This PCB is ready already, because i am re-using it from a previous project that I gave up for a certain reason, before really testing it. I am a bit afraid to blow my PIC with the EMF generated by the sttepper. Can I use this circuit or should I make another PCB and use some diodes, some other resistors, etc?

Thanks a lot for any help.

Rafael Cordeiro

 

[rafael_cordeiro]

It seems that the picture isn´t loading.
There it goes

 

[bloody-orc]

1) yes you can do it like that

2) the diodes are in the ULN as you can also see in the datasheet

 

[spirosd]

You might also consider adding a zener diode on pin 9 to help the uln diodes redirect back emf to the power lines.

If you are really concerned about the pic, you can always isolate the inputs to the uln using optocouplers.

On an aside, I have been working on something very similar. You can also use the pwm module on the 16f628a to control the power line to the motor. You can then use a higher voltage to energise the coils, but keep the amps down.