Force Sensitive Resistor
Another kind of analog input we can use is a force sensitive resistor (FSR). This is a resistor whose resistance changes depending on how much pressure is applied to it. It looks like this:
There is nothing special going on with the materials here. The FSR is just a device made from two layers of metal separated by a spacer. The harder you press, the more the layers of metal touch one another through the spacer.
FSRs are not polarized, so it doesn’t matter which leg goes toward high and which goes toward ground. However, to make the resistance readable, we need to use the FSR in a circuit with another resistor, and measure the voltage in the middle. The connection between the FSR and the brown, black, and orange striped resistor should be connected to an analog input on the Arduino. That setup (called a voltage divider configuration) looks like this:
The FSR is useful if you want to know exactly how much it is being pressed. It can also be used to detect rollover events by your pinball, but a fun way to use it is to measure how hard a pinball smashes into it, and control outputs (or score) accordingly.