The resistor will get warm - thats heat which would otherwise have ended up in the controller chip and the motor. By putting a 100 ohm resistor in, the current gets 'slowed' down by the resistor, so stops much quicker. Thats bad for speed, because for the motor to turn fast, it's vital that the current stop as quick as possible. These diodes allow current to continue flowing for a moment in a coil of the motor after that coil has been switched off (hence the name 'freewheel'). The jumper is used to connect the freewheel diodes on the driver chip. You should get even more speed with libraries which smoothly accelerate the stepper. With the default arduino stepper library, I am able to move at 700 rpm, whereas with default wiring, I am limited to 450 rpm.
Pin 4 connect to 5v power (and the other end of the resistor from pin 2.
The cheap ULN2003 Motor driver board often supplied with the 28BYJ-48 cheap ($1) 5v stepper motor has a 'mystery jumper' on it.īy removing the jumper and adding a resistor, one can nearly double the torque while the motor is turning, while also keeping both the motor and controller cooler.
