This machine uses a capacitive sensor and 3D-printed slide to drop promotional buttons when it senses a finger in the designated circle.
Mechanism is a simple escapement on a timer. The bottom servo drops a button, while the top holds most of it in place. The I/O and program setup is very simple, just a single capacitive sensor as an input, and two servos as outputs. I also added a capacitor on the sensor shield to help account for spikes due to servo motors.