This cassette player modification controls the player's motor directly with an L9110 motor driver. An Adafruit QT Py RP2040 controls the L9110 with two PWM pins and uses CircuitPython code to affect the motor's throttle by reading a potentiometer value.
This mod should be used with a cassette tape loop. By driving the motor independently from the cassette player's circuit board, you can damage regular cassette tapes since the motor will keep spinning the tape even once the tape has reached the end.
The circuit is built on a perma-proto board that fits perfectly on the back of the cassette player with a 3D printed plate. The QT Py RP2040 can power the audio output of the player with its 3.3V output.
The potentiometer affects the speed and direction of the motor being driven by the L9110 driver. If you turn the potentiometer all the way to the left, the motor throttles at full speed in reverse. If you turn the potentiometer all the way to the right, the motor throttles forward at full speed.
The button controls a revved warble effect when it is held down. The motor will perform the effect forward or reversed depending on the position of the potentiometer.