Hello,
This schematics from Interlink shows how to digitize the measure of resistance on multiple channels through a RC circuit.
This is the description of the circuit's operation:
"Sampling Cycle (any FSR channel):
The microcontroller switches to a specific FSR channel, toggling it high, while all other FSR channels are toggled low. The RESET channel is toggled high, a counter starts and the capacitor C1 charges, with its charging rate controlled by the resistance of the FSR (t ~ RC). When the capacitor reaches the high digital threshold of the INPUT channel, the counter shuts off, the RESET is toggled low, and the capacitor discharges.
The number of “counts” it takes from the toggling of the RESET high to the toggling of the INPUT high is proportional to the resistance of the FSR. The resistors RMIN and RMAX are used to set a minimum and maximum “counts” and therefore the range of the “counts.” They are also used periodically to re-calibrate the reference. A sampling cycle for RMIN is run; the number of “counts” is stored and used as a new zero. Similarly, a sampling cycle for RMAX is run and the value is stored as the maximum range (after subtracting the RMIN value). Successive FSR samplings are normalized to the new zero. The full range is “zoned” by dividing the normalized maximum “counts” by the number of desired zones. This will delineate the window size or width of each zone.
Continual sampling is done to record changes in FSR resistance due to changes in force. Each FSR is selected sequentially."
I have read the Capacitance Meter and RC Time Constants example and now I don't see the goal of the circuit's section circled in red. Is it required, as either a calibration or an FSR selection channel act as the capacitor charging pin already?
Thank you in advance.