cartreader/extras/control/README.md

This is a simple Windows application to control the Cart Reader without the need of an OLED screen or buttons.
Files are still loaded from and saved to the SD card.

Configure the switches like so and use the USB port at the left side of the Arduino Mega:

To enable the Serial Monitor follow the instructions on flashing the Cart_Reader sketch to the Arduino as shown here: How to flash the Arduino Code to your Cart Reader.
But before you hit upload you need to change two lines in the Cart_Reader tab.