Stepper motor noise in 1 direction

[AnalogKid2DigitalMan]

I would think more important than the voltage output of the supply is the current rating of the supply- does it have enough current to supply the motor?

Motor loads can be different for different directions when mechanics are involved, especially if the motor is moving a load up or down (gravity is involved).

-AK2DM

[ATMA]

Tried the function generator, no change


Well, for the current i current limited it at a certain value at the source. The motor draws whatever current it needs.

[ATMA]

I've tried troubleshooting the driver pin by pin and i noticed something.

The motor direction is controlled by the Dir pin on the driver. This driver pin is in turn controlled through  DIO of my DAQ card. For me to turn in the 'noisy' direction, my pin has to be pulled LOW. When i tried connecting this pin directly to D Gnd, the noise stops and the motor runs smoothly.

This is kinda wierd, so i tried probing my original DIO pin which controls the Dir signal with HIGH and LOW and everything seems ok, high is 5 and low is 0. I tried swapping with other DIO pins, and it's still the same.

Is there some way to rectify this? Is my LOW not 'low' enough?

[Buechsenschuetz]

You have to check the input specs of the driver circuitry you are using for proper interfacing to your DAC card. Remeber that not only voltage level is an issue to be consired - you should also check the output impedance of the pin used for the DIR signal. Remember that a TTL circuit typically needs less than 0.8V to detect a low signal - but the driving circuit has to sink approx. 400uA of current. Also, you always need some "head room" on the voltage levels to have a safety margin. So again, check the output specs of the controller unit and the input specs of the driver circuit carefully before connecting them.

[ATMA]

Thanks Buechsenschuetz, in that case i'll try Jochen's idea using a buffer to drive the pin. Thanks!

[Buechsenschuetz]

If you are going to use a buffer to "amplify" the TTL signal, you can use a 74LS14. This one has a certain hysteresis on the input and will be more immune to noise on the signal line. If your driver unit needs somewhat more input current (i.e. if you are using optoisolators - which I would strictly recommend to separate a high-voltage circuit from a TTL-level circuit) you can use devices like the 74LS243. It has input hysteresis (similar to the 'LS14) but much more drive capability.