The purpose of a serial resistor in a matrix keypad is to prevent ghosting. Ghosting is when multiple keys are pressed at the same time and only one key appears to be registered. This can be caused by two keys being close to each other and accidentally being pressed at the same time, or by electrical interference between neighboring keys on the keypad matrix. The serial resistor helps to prevent ghosting by ensuring that only one key is activated at a time. When a key is pressed, it completes the electrical circuit between two rows of contacts on...