Temperature & Humidity

1#include <stdint.h>
2#include <stdbool.h>
3#include "inc/hw_memmap.h"
4#include "driverlib/sysctl.h"
5#include "driverlib/gpio.h"
6#include "driverlib/timer.h"
7 
8#define LED_ALL  (GPIO_PIN_1 | GPIO_PIN_2 | GPIO_PIN_3)
9#define DHT_PORT GPIO_PORTA_BASE
10#define DHT_PIN  GPIO_PIN_2   // PA2
11#define PWM_STEPS 256
12 
13static void showColor(uint8_t r, uint8_t g, uint8_t b, uint32_t periods) {
14    volatile uint32_t p, i;
15    for (p = 0; p < periods; p++)
16        for (i = 0; i < PWM_STEPS; i++) {
17            uint8_t out = 0;
18            if (i < r) out |= GPIO_PIN_1;
19            if (i < g) out |= GPIO_PIN_3;
20            if (i < b) out |= GPIO_PIN_2;
21            GPIOPinWrite(GPIO_PORTF_BASE, LED_ALL, out);
22            SysCtlDelay(2);
23        }
24}
25 
26static void delayMs(uint32_t ms) { SysCtlDelay((SysCtlClockGet() / 3000) * ms); }
27static void delayUs(uint32_t us) { SysCtlDelay((SysCtlClockGet() / 3000000) * us); }
28 
29static void dhtPinOut(void) { GPIOPinTypeGPIOOutput(DHT_PORT, DHT_PIN); }
30static void dhtPinIn(void) {
31    GPIOPinTypeGPIOInput(DHT_PORT, DHT_PIN);
32    GPIOPadConfigSet(DHT_PORT, DHT_PIN, GPIO_STRENGTH_2MA, GPIO_PIN_TYPE_STD_WPU);
33}
34static int dhtLevel(void) { return GPIOPinRead(DHT_PORT, DHT_PIN) ? 1 : 0; }
35 
36// Read 5 bytes from the DHT11. Returns 1 on success, 0 on error/timeout.
37static int dhtRead(uint8_t data[5]) {
38    uint32_t i, start, us, timeout;
39    for (i = 0; i < 5; i++) data[i] = 0;
40 
41    dhtPinOut();                                          // start: hold low >= 18 ms
42    GPIOPinWrite(DHT_PORT, DHT_PIN, 0);
43    delayMs(20);
44    GPIOPinWrite(DHT_PORT, DHT_PIN, DHT_PIN);
45    delayUs(30);
46    dhtPinIn();
47 
48    timeout = 100000; while (dhtLevel() != 0) if (--timeout == 0) return 0;  // ack low
49    timeout = 100000; while (dhtLevel() == 0) if (--timeout == 0) return 0;  // ack high
50    timeout = 100000; while (dhtLevel() != 0) if (--timeout == 0) return 0;  // bit0 low
51 
52    for (i = 0; i < 40; i++) {
53        timeout = 100000; while (dhtLevel() == 0) if (--timeout == 0) return 0; // 50us low ends
54        start = TimerValueGet(TIMER0_BASE, TIMER_A);
55        timeout = 100000; while (dhtLevel() != 0) if (--timeout == 0) return 0; // measure high
56        us = (TimerValueGet(TIMER0_BASE, TIMER_A) - start) / 50;               // 50 MHz -> us
57        data[i / 8] <<= 1;
58        if (us > 45) data[i / 8] |= 1;                   // long high = 1
59    }
60    if ((uint8_t)(data[0] + data[1] + data[2] + data[3]) != data[4]) return 0; // checksum
61    return 1;
62}
63 
64int main(void) {
65    SysCtlClockSet(SYSCTL_SYSDIV_4 | SYSCTL_USE_PLL |
66                   SYSCTL_OSC_MAIN | SYSCTL_XTAL_16MHZ);
67 
68    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOF);
69    while (!SysCtlPeripheralReady(SYSCTL_PERIPH_GPIOF)) {}
70    GPIOPinTypeGPIOOutput(GPIO_PORTF_BASE, LED_ALL);
71 
72    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOA);
73    while (!SysCtlPeripheralReady(SYSCTL_PERIPH_GPIOA)) {}
74    dhtPinIn();
75 
76    SysCtlPeripheralEnable(SYSCTL_PERIPH_TIMER0);         // free-running us timer
77    while (!SysCtlPeripheralReady(SYSCTL_PERIPH_TIMER0)) {}
78    TimerConfigure(TIMER0_BASE, TIMER_CFG_PERIODIC_UP);
79    TimerLoadSet(TIMER0_BASE, TIMER_A, 0xFFFFFFFF);
80    TimerEnable(TIMER0_BASE, TIMER_A);
81 
82    while (1) {
83        uint8_t d[5];
84        if (dhtRead(d)) {
85            int32_t tmp = d[2];                           // d[0]=humidity%, d[2]=temp C
86            if (tmp < 18) tmp = 18;                       // map 18..40 C
87            if (tmp > 40) tmp = 40;
88            int32_t lv = ((tmp - 18) * 255) / 22;         // 0..255
89            if (lv < 128) showColor(0, lv * 2, 255 - lv * 2, 40);        // cool -> blue
90            else          showColor((lv - 128) * 2, 255 - (lv - 128) * 2, 0, 40); // warm -> red
91        } else {
92            showColor(60, 25, 0, 10);                     // read failed -> amber blink
93            showColor(0, 0, 0, 5);
94        }
95        delayMs(1500);                                    // DHT11 is slow: >= 1 s between reads
96    }
97}