I had a stepper motor that I salvaged from an old canon printer and I wired it up to the arduino.
I used the two-pin version of the control circuits shown here.
However, I noticed that even when the motor power supply (i.e the one on pin '8') was not connected to the IC, the stepper kept on turning. (At faster speeds, the servo wasn't able to function properly, without the motor power supply. )
Is this normal? Or have I made a mistake in the wiring?
You are probably frying one of the protection diodes on the chip - the motor supply must be present and at least as high as the logic supply according to the datasheet - don't do this!
Thanks for the reply.
I also tried connecting a 12 volt supply to the Vin pin...
Then the motor jst vibrates instead of stepping properly.
what do you think is wrong?
But it works if you power the Arduino from the USB instead? Probably severe noise on the motor supply - best not to derive logic supply from a motor circuit, logic demands a clean power supply, motors can generate spikes and overwhelm their supply on start up leading to supply drop-outs.
Sorry.. When I said 'Vin' pin, I was referring to the Vin pin on the H-bridge IC. (The pin used for the motor power supply).
I tried connecting a 12V battery as well as a 9V 'wal-art' to the motor supply pin. Both give the same problem.. the motor just vibrates.
Perhaps one winding isn't being driven? Try multimeter and very slow stepping to verify each winding gets driven both directions in sequence
I ran into the same problem once. It seems to be a wiring fault.
So i make a drawing to clearafy the schematics and solved it.
Maybe it can help you to understand the principle.
The darlington number represents the in/output used on the chip.
2wire principle.pdf (6.99 KB)