[PD] pduino and FSRs

Martin Peach martin.peach at sympatico.ca
Sat Apr 12 18:29:54 CEST 2008

Derek Holzer wrote:
> This makes sense. I used some FSRs with a hacked joystick HID device and 
> got into some trouble there as well. FSRs have zero resistance when no 
> force is applied, so essentially you are short circuiting the 5v 
> directly to ground when you plug them in without any force applied. I 
> would definitely try a resistor in series with each FSR, that's how I 
> did it with the HID joystick, which also crashed (the joystick did not 
> function) when the FSR was plugged in without any resistance.

FSR have a very _high_ resistance with no force. The resistance goes 
down when you apply pressure. The circuit needs to look like this:

+------analog in

This will give a number that goes down as force is applied. If you want 
the number to increase, switch the 10k and FSR.

Looking at the (considerably more expensive than a 10k resistor) phidget 
voltage divider I see that the resistance is a multi-turn 1Meg 
potentiometer. If it is set to zero ohms then pressing a sensor will 
short out the power supply.
Also by convention the red wire is 5V, the black wire is ground and the 
white is the analog signal.


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