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