# Problems with Stepper Motor & SN754410

I am using a stepper motor for a project, it is the first time I've used one. The internet said it was very simple and easy but that's not true for me.

I bought this motor from digikey

https://www.digikey.ca/product-detail/en/digilent-inc/290-028/1286-1219-ND/7068780

and used this tutorial to wire it up. Except mine is a 5V stepper motor.

https://itp.nyu.edu/physcomp/labs/motors-and-transistors/lab-controlling-a-stepper-motor-with-an-h-bridge/

I used the Arduino stepper motor one revolution example. Set the stepsPerRevolution to 64 as per data sheet.

The motor turns less than a quarter turn, no torque and only draws 8mA. I can not get it to a full revolution or have any torque.

• Do you have a schematic of your driver and the connection to the motor? Are you using the 5 volt supply for the motor? – whitegreg56 Dec 6 '18 at 3:30
• Generally steppers should be driven with a voltage several times the rating feeding into a chopping current regulator. Your SN754410 is a horribly lossy and antiquated device which will drop a fair fraction of your supply across its two darlingtons, making the situations yet worse. – Chris Stratton Dec 6 '18 at 4:34

You CANNOT use a SN754410 to drive a 5V stepper motor successfully.

The output circuit looks like this:

The output high and low includes two Vbe drops in it, so from your 5V supply at least 2.4V is lost. Driving the stepper motor with only 2.6V is unlikely to work.

You would have to raise your VCC2 to about 7.5V to get it to work. You may be better in raising the voltage to 9V and include a series resistor to reduce the current to the rated value.

Your motor has a 120 Ohm winding (I assume half winding), so is rated for 42mA @5V. If you raise VCC2 to 9V, and use a 33 Ohm series resistor for each half winding you'd get about the right current flow. The higher aiming voltage will give you slightly better pullout torque during switching.

NOTE that in the lab you point to, they connected the motor supply VCC2 to 12V ….not 5V.

You should test your winding current by connecting the center tap to +5V and one of the endpoint windings to Gnd. Whatever that current is will tell you the resistance of the half winding