I have a 17PM-K307-05VS unipolar stepper motor. I am building the driver for the stepper motor. The exact rated voltage and current are unknown, it seems the motor is old or discontinued, but the measured coil resistance is 6.6 ohms. For this, I am not using an IC, I am using the TIP120 darlington transistor as a switch. The picture will show the circuit of one coil of the stepper motor and the darlington connected.
My problem is when the arduino sends pulses to turn on or off the transistor, no current flows through the darlington when its on. Is this has to do with the low logic voltage? How can I resolve this problem? is there any ideas to improve my circuit or is there something wrong in the circuit?Also I noted when I turn on the circuit the base to emmitter current drops down to .324V, which is low. Any advice will be of great help!