mirror of https://github.com/joan2937/pigpio
95 lines
2.0 KiB
C
95 lines
2.0 KiB
C
#include <stdio.h>
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#include <pigpio.h>
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/*
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Measure how long a capacitor takes to charge through a resistance.
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A potentimeter is used to vary the resistance.
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The time taken will be proportional to the resistance.
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3V3 ----- Potentiometer --+-- Capacitor ----- Ground
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+-- gpio
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gcc -o pot_cap_charge pot_cap_charge.c -lpigpio -lpthread -lrt
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sudo ./pot_cap_charge
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*/
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#define GPIO 25
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#define MAX_READING 1000
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static uint32_t rechargeTick = 0;
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void callback(int gpio, int level, uint32_t tick)
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{
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static uint32_t smooth = 0;
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static int reading = 0;
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uint32_t raw;
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if (level == 1) /* measure recharge time */
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{
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++reading;
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if (rechargeTick)
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{
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raw = tick - rechargeTick; /* set in main */
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if (raw < MAX_READING) /* ignore outliers */
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{
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/* smooth using 0.8 * smooth + 0.2 * raw */
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smooth = (raw + (4 * smooth)) / 5;
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printf("%d %d %d\n", reading, raw, smooth);
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}
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else
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{
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/* ignore outlier, set dot at fixed position */
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printf("%d %d %d\n", reading, 40, smooth);
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}
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}
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else
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{
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/* ignore reschedule, set dot at fixed position */
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printf("%d %d %d\n", reading, 20, smooth);
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}
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}
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}
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int main (int argc, char *argv[])
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{
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uint32_t t1, t2;
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int tDiff;
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if (gpioInitialise()<0) return 1;
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gpioSetAlertFunc(GPIO, callback); /* callback when GPIO changes state */
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while (1)
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{
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gpioWrite(GPIO, PI_OFF); /* drain capacitor */
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gpioDelay(200); /* microseconds */
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t1 = gpioTick();
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gpioSetMode(GPIO, PI_INPUT); /* start capacitor recharge */
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t2 = gpioTick();
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/* dump reading if rechargeTick not accurate to 3 micros */
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if ((t2 - t1) < 3) rechargeTick = t1; else rechargeTick = 0;
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gpioDelay(5000); /* microseconds, nominal 200 readings per second */
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}
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gpioTerminate();
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}
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