This is a tiny circuit that takes PWM (RC servo) inputs on pin PB0 and uses them to control stepper motor operation on pins PB1-4.

I have designed the PCB to use very inexpensive motor drivers, capable of about 0.5A drive.

Max voltage into the board should be limited to 5v (like normal RC servos).

The Code is available on Github (https://github.com/dagnall53/ATTINY_RC_Stepper_servo).

Video of operation is here https://youtu.be/CbauUchePao

Photo and video are of a slightly earlier version. This design here is an improved layout with some decoupling capacitors, and better location stencil for the stepper motor film wire location on the rear, but otherwise the circuit is the same.

There are extra motor pads so you can easily connect to the motor using long wires. I soldered mine by first tinning both the board and the film wire, then aligning the film wire on the board and carefully heating with a heat gun until the solder melted. YOU must be careful not to short the connections when you do this! Which is why there is an extra set of pads on the back to make testing for shorts easy. You should get a reading of about 18 ohms across each winding and no connection between the two windings.

When you turn on, the motors will drive to (0).

You can add a 100k resistor from PB5 to ground to switch to "analogue" mode with the standard code for testing, but I would recommend just modifying the code to use whichever version you prefer for your project.

Once programmed, using the ICP, you can break off the ICP part of the board to make a smaller PCB.

https://youtu.be/CbauUchePao