In the circuit below, I'm trying to replace the physical switch on the 'flipper opto switch board' (and 'power driver board') with a transistor, controlled by Arduino.
My understanding (please correct where I am wrong, learner here) is that I should be able to use a NPN transistor, with Collector tied to the 12v feed from the fliptronics board. The transistor needs to be able to pass 12V at ~12ma
I have tried using a 2n4401 that I have stock of, and I believe this has a hfe of 80, so I run the 5v arduino output through a 2k resistor, which should pass around 0.25ma to the base? (And be enough to switch the transistor 'on', dragging the 12v feed to the LM339 down to below 5v)
But nothing happens.
Entirely likely I'm making a fundamental error here, but I'm not sure what it is. Any help appreciated.