The control program on the ESP32 communicates with the laptop through the serial port. It gets the commands with characters and communicates back when the stepper motor is finished. I kept it simple. The first command is to forward a frame. That is 'A'. The upper case letter is for the first stepper motor (the tooth wheel) and the lower case letter for the other stepper motor at the reel. 'B' and 'b: are a frame backward. Cc and Dd are for a single step. Ee and Ff for continuous turning. (And later Gg and HH for a third frame.) It replies with E1 and E2 when the turning is finished. (In hindsight I should have used E and e). Also the speed and the acceleration can be adjusted with WwXx for halving and doubling the acceleration and YyZz for the speed.

A friend once told me: don’t write any code yourself; everything is already written. That’s true. For every task several libraries have been written and the Arduino IDE let you choose the one you like. The most time goes into choosing the library.

An important condition is to be able to have two stepper motors turning simultaneously. So the routines should be non-blocking. I settled for AccelStepper. It also has the nice feature that it can slowly accelerate and decelerate. In this way the film is protected against a too aggressive tooth wheel.

The only function missing is a callback function when the stepper motor is finished turning. I wanted to include ths function using inheritance, but for some unknown reason I did not get this working, even after trying for a whole evening. So I went for the quick and dirty way to just add functions and duplicate them for the two steppers.

The ESP32 source code is in the file section.