Having trouble understanding the wiring....

[Leech_hunter]

So I'm taking the plunge and building a MAME cabinet.  Been reading and watching videos on and off for about a year.   I'm going to be using an Ultimarc IPAC ultimate IO board.

Im struggling to understand how it actually works in regards to how the board sends signals to the computer.  When I hit a pushbutton, does the voltage flow from the common/ground through the pushbutton microswitch, to the IO board pin?  Does it flow from the IO pin through the pushbutton and completes the circuit at the ground?

I assume it's the second question.  Is there no voltage potential on the IO pins unless it can complete the circuit to the ground (-)?!  Otherwise the pins would all be constantly firing.  Can someone explain how the pushbutton actually makes the IO pin send a keystroke to the computer?

[PL1]

The type of circuit you're describing is an "active high" device such as a light fixture.
- When you flip the switch to "on", voltage is applied to the bulb causing it to light up.

Like most modern encoders, the IPac is an "active low" device that uses a pull-up resistor to apply a logic high (5v) to the input logic gate.
- When you press the button, the logic gate input is dragged down to ground. (logic low)



In plumbing terms, it's like flushing the toilet while someone is taking a shower.

The sudden drop in cold-water pipe pressure (voltage) causes a change in the hot/cold balance that triggers an output  .


Scott

[Leech_hunter]

Thank you!!  Makes sense