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Test Soource to find problem with Raspberry PI and DHT 22
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// How to access GPIO registers from C-code on the Raspberry-Pi | |
// Example program | |
// 15-January-2012 | |
// Dom and Gert | |
// | |
// Access from ARM Running Linux | |
#define BCM2708_PERI_BASE 0x20000000 | |
#define GPIO_BASE (BCM2708_PERI_BASE + 0x200000) /* GPIO controller */ | |
#include <stdio.h> | |
#include <string.h> | |
#include <stdlib.h> | |
#include <dirent.h> | |
#include <fcntl.h> | |
#include <assert.h> | |
#include <unistd.h> | |
#include <sys/mman.h> | |
#include <sys/types.h> | |
#include <sys/stat.h> | |
#include <sys/time.h> | |
#include <bcm2835.h> | |
#include <unistd.h> | |
#define MAXTIMINGS 100 | |
//#define DEBUG | |
#define DHT11 11 | |
#define DHT22 22 | |
#define AM2302 22 | |
int readDHT(int type, int pin); | |
int main(int argc, char **argv) | |
{ | |
if (!bcm2835_init()) | |
return 1; | |
if (argc != 3) { | |
printf("usage: %s [11|22|2302] GPIOpin#\n", argv[0]); | |
printf("example: %s 2302 4 - Read from an AM2302 connected to GPIO #4\n", argv[0]); | |
return 2; | |
} | |
int type = 0; | |
if (strcmp(argv[1], "11") == 0) type = DHT11; | |
if (strcmp(argv[1], "22") == 0) type = DHT22; | |
if (strcmp(argv[1], "2302") == 0) type = AM2302; | |
if (type == 0) { | |
printf("Select 11, 22, 2302 as type!\n"); | |
return 3; | |
} | |
int dhtpin = atoi(argv[2]); | |
if (dhtpin <= 0) { | |
printf("Please select a valid GPIO pin #\n"); | |
return 3; | |
} | |
printf("Using pin #%d\n", dhtpin); | |
readDHT(type, dhtpin); | |
return 0; | |
} // main | |
int bits[250], data[100]; | |
int bitidx = 0; | |
int readDHT(int type, int pin) { | |
int counter = 0; | |
int laststate = HIGH; | |
int j=0; | |
// Set GPIO pin to output | |
bcm2835_gpio_fsel(pin, BCM2835_GPIO_FSEL_OUTP); | |
bcm2835_gpio_write(pin, HIGH); | |
usleep(500000); // 500 ms | |
bcm2835_gpio_write(pin, LOW); | |
usleep(20000); | |
bcm2835_gpio_write(pin, HIGH); | |
bcm2835_gpio_fsel(pin, BCM2835_GPIO_FSEL_INPT); | |
data[0] = data[1] = data[2] = data[3] = data[4] = 0; | |
// wait for pin to drop? | |
int saveGuard = 0; | |
while (bcm2835_gpio_lev(pin) == 1 && saveGuard < 50000) { | |
usleep(1); | |
saveGuard++; | |
} | |
if (saveGuard >= 50000) | |
{ | |
printf("No answer ?!\n"); | |
return; | |
} | |
// read data! | |
for (int i=0; i< MAXTIMINGS; i++) { | |
counter = 0; | |
while ( bcm2835_gpio_lev(pin) == laststate) { | |
counter++; | |
//nanosleep(1); // overclocking might change this? | |
if (counter == 1000) | |
break; | |
} | |
laststate = bcm2835_gpio_lev(pin); | |
if (counter == 1000) break; | |
bits[bitidx++] = counter; | |
if ((i>3) && (i%2 == 0)) { | |
// shove each bit into the storage bytes | |
data[j/8] <<= 1; | |
if (counter > 200) | |
data[j/8] |= 1; | |
j++; | |
} | |
} | |
#ifdef DEBUG | |
for (int i=3; i<bitidx; i+=2) { | |
printf("bit %d: %d\n", i-3, bits[i]); | |
printf("bit %d: %d (%d)\n", i-2, bits[i+1], bits[i+1] > 200); | |
} | |
#endif | |
printf("Data (%d): 0x%x 0x%x 0x%x 0x%x 0x%x\n", j, data[0], data[1], data[2], data[3], data[4]); | |
if ((j >= 39) && | |
(data[4] == ((data[0] + data[1] + data[2] + data[3]) & 0xFF)) ) { | |
// yay! | |
if (type == DHT11) | |
printf("Temp = %d *C, Hum = %d \%\n", data[2], data[0]); | |
if (type == DHT22) { | |
float f, h; | |
h = data[0] * 256 + data[1]; | |
h /= 10; | |
f = (data[2] & 0x7F)* 256 + data[3]; | |
f /= 10.0; | |
if (data[2] & 0x80) f *= -1; | |
printf("Temp = %.1f *C, Hum = %.1f \%\n", f, h); | |
} | |
return 1; | |
} | |
return 0; | |
} |
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