For this discussion, impedance is just a fancy way of saying resistance and is represented by R2 in the picture above. An input pin on a microcontroller has an impedance that can vary from 100k-1MΩ. The general rule for condition 2 is to use a pull-up resistor (R1) that is an order of magnitude (1/10th) less than the input impedance (R2) of the input pin. A 4MΩ resistor might work as a pull-up, but its resistance is so large (or weak) that it may not do its job 100% of the time. You generally want a large resistor value (10kΩ), but you don’t want it too large as to conflict with condition 2. The lower the resistance, the more power will be used when the button is hit. The value of the pull-up resistor controls the voltage on the input pin.įor condition 1, you don't want the resistor's value too low. When the button is not pressed, the input pin is pulled high. The value of resistor R1 controls how much current you want to flow from VCC, through the button, and then to ground. When the button is pressed, the input pin is pulled low. The value of the pull-up resistor needs to be chosen to satisfy two conditions:
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