modified 1 year ago

Pull-up Pull-Down Resistors

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The voltmeters represent a logic pin on a microcontroller.

Left is a pull-up. Signal is High with switch open.

Right is a pull-down. Signal is Low with switch open.

Bottom are without the resistor. They will short out when you close the switch.

The resistor acts as a current limiter, without it the circuit would short when closed, and float when open. It also creates a voltage differential. When the circuit is complete, "Upstream" of the resistor will have a higher voltage.

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