FSR: Explain it to me like I’m five.
I have the FSR’s wired in parallel. They show a change in resistance like you’d expect.
Folks say they ‘wire them right up to Z_min’.
But Z-min is really a three wire header. Ground, +5V and signal.
So which two wires to I use? Is it +5V and signal? It doesn’t seem to be ground and signal.
350g is a significant value, do I tune the contact patches so that it just comes off ‘infinite resistance’ at 350g?
The three FSRs wired in parallel form a single resistor. With one side connected to ground and the other connected to a digital pin with the internal pull-up enabled, this forms a voltage divider that looks like this:
+5V-----internal pull-up resistor-----digital pin------FSRs-----GND
The voltage drop across the entire voltage divider is 5V, but whether more of that voltage is dropped across the pull-up or the FSRs depends on which has higher resistance. As any one of the FSRs decreases its resistance relative to the fixed resistance of the pull-up, the voltage on the digital pin drops because the FSR drops less voltage and pull-up must drop more. The digital pin has a voltage threshold below which it will read LOW and above which it will read HIGH. There’s actually a zone of uncertainty between these, but the voltage crosses this quickly enough that it doesn’t really matter. As soon as the digital pin gets a LOW reading, the endstop is triggered.