I tried wiring my Eheim auto feeder and found it has a different design from what is shown in the instructions. It is no longer as simple as pulling the button pin up or down; I tried all the combinations. Instead I added this NPN transistor to act as a switch between the two button pins. It works when I connect the base to 3.3V. However, it seems that the Robo-Tank feeder port alternates between 0V and floating (~0.1V) so it cannot trigger the transistor. Is there some configuration to change this? Or should I just use a DC port with a voltage divider?
