DEBJYOTI SINHA
DHT sensor for measuring temperature
Diff: DHT.cpp
- Revision:
- 2:df22ddf10d75
- Parent:
- 1:25c96950b6ed
- Child:
- 3:6937e130feca
- Child:
- 4:171c12efa794
diff -r 25c96950b6ed -r df22ddf10d75 DHT.cpp
--- a/DHT.cpp Wed Jul 24 06:59:28 2013 +0000
+++ b/DHT.cpp Fri Aug 15 20:55:43 2014 +0000
@@ -9,7 +9,7 @@
*
* Copyright (C) Wim De Roeve
* based on DHT22 sensor library by HO WING KIT
- * Arduino DHT11 library
+ * Arduino DHT11 library
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documnetation files (the "Software"), to deal
@@ -32,113 +32,99 @@
#include "DHT.h"
-#define DHT_DATA_BIT_COUNT 41
+#define DHT_DATA_BIT_COUNT 40
-DHT::DHT(PinName pin,int DHTtype) {
+DHT::DHT(PinName pin, eType DHTtype)
+{
_pin = pin;
_DHTtype = DHTtype;
- _firsttime=true;
+ _firsttime = true;
+}
+
+DHT::~DHT()
+{
+
}
-DHT::~DHT() {
+eError DHT::stall(DigitalInOut &io, int const level, int const max_time)
+{
+ int cnt = 0;
+ while (level == io) {
+ if (cnt > max_time) {
+ return ERROR_NO_PATIENCE;
+ }
+ cnt++;
+ wait_us(1);
+ }
+ return ERROR_NONE;
}
-int DHT::readData() {
- int i, j, retryCount,b;
- unsigned int bitTimes[DHT_DATA_BIT_COUNT];
+eError DHT::readData()
+{
+ uint8_t i = 0, j = 0, b = 0, data_valid = 0;
+ uint32_t bit_value[DHT_DATA_BIT_COUNT] = {0};
eError err = ERROR_NONE;
time_t currentTime = time(NULL);
DigitalInOut DHT_io(_pin);
- for (i = 0; i < DHT_DATA_BIT_COUNT; i++) {
- bitTimes[i] = 0;
- }
-#if 0
- if (!_firsttime) {
- if (int(currentTime - _lastReadTime) < 2) {
- err = ERROR_NO_PATIENCE;
- return err;
- }
- } else {
- _firsttime=false;
- _lastReadTime=currentTime;
+ // IO must be in hi state to start
+ if (ERROR_NONE != stall(DHT_io, 0, 250)) {
+ return BUS_BUSY;
}
-#endif
- retryCount = 0;
- do {
- if (retryCount > 125) {
- err = BUS_BUSY;
- return err;
- }
- retryCount ++;
- wait_us(2);
- } while ((DHT_io==0));
-
-
+ // start the transfer
DHT_io.output();
DHT_io = 0;
- wait_ms(18);
+ // only 500uS for DHT22 but 18ms for DHT11
+ (_DHTtype == 11) ? wait_ms(18) : wait(1);
DHT_io = 1;
- wait_us(40);
+ wait_us(30);
DHT_io.input();
-
- retryCount = 0;
- do {
- if (retryCount > 40) {
- err = ERROR_NOT_PRESENT;
- return err;
- }
- retryCount++;
- wait_us(1);
- } while ((DHT_io==1));
-
- if (err != ERROR_NONE) {
- return err;
+ // wait till the sensor grabs the bus
+ if (ERROR_NONE != stall(DHT_io, 1, 40)) {
+ return ERROR_NOT_PRESENT;
}
-
- wait_us(80);
-
+ // sensor should signal low 80us and then hi 80us
+ if (ERROR_NONE != stall(DHT_io, 0, 100)) {
+ return ERROR_SYNC_TIMEOUT;
+ }
+ if (ERROR_NONE != stall(DHT_io, 1, 100)) {
+ return ERROR_NO_PATIENCE;
+ }
+ // capture the data
for (i = 0; i < 5; i++) {
for (j = 0; j < 8; j++) {
-
- retryCount = 0;
- do {
- if (retryCount > 75) {
- err = ERROR_DATA_TIMEOUT;
- return err;
- }
- retryCount++;
- wait_us(1);
- } while (DHT_io == 0);
+ if (ERROR_NONE != stall(DHT_io, 0, 75)) {
+ return ERROR_DATA_TIMEOUT;
+ }
+ // logic 0 is 28us max, 1 is 70us
wait_us(40);
- bitTimes[i*8+j]=DHT_io;
-
- int count = 0;
- while (DHT_io == 1 && count < 100) {
- wait_us(1);
- count++;
+ bit_value[i*8+j] = DHT_io;
+ if (ERROR_NONE != stall(DHT_io, 1, 50)) {
+ return ERROR_DATA_TIMEOUT;
}
}
}
- DHT_io.output();
- DHT_io = 1;
+ // store the data
for (i = 0; i < 5; i++) {
b=0;
for (j=0; j<8; j++) {
- if (bitTimes[i*8+j+1] > 0) {
- b |= ( 1 << (7-j));
+ if (bit_value[i*8+j] == 1) {
+ b |= (1 << (7-j));
}
}
DHT_data[i]=b;
}
- if (DHT_data[4] == ((DHT_data[0] + DHT_data[1] + DHT_data[2] + DHT_data[3]) & 0xFF)) {
+ // uncomment to see the checksum error if it exists
+ //printf(" 0x%02x + 0x%02x + 0x%02x + 0x%02x = 0x%02x \n", DHT_data[0], DHT_data[1], DHT_data[2], DHT_data[3], DHT_data[4]);
+ data_valid = DHT_data[0] + DHT_data[1] + DHT_data[2] + DHT_data[3];
+ if (DHT_data[4] == data_valid) {
_lastReadTime = currentTime;
- _lastTemperature=CalcTemperature();
- _lastHumidity=CalcHumidity();
+ _lastTemperature = CalcTemperature();
+ _lastHumidity = CalcHumidity();
} else {
err = ERROR_CHECKSUM;
@@ -148,7 +134,8 @@
}
-float DHT::CalcTemperature() {
+float DHT::CalcTemperature()
+{
int v;
switch (_DHTtype) {
@@ -167,21 +154,25 @@
return 0;
}
-float DHT::ReadHumidity() {
+float DHT::ReadHumidity()
+{
return _lastHumidity;
}
-float DHT::ConvertCelciustoFarenheit(float celsius) {
+float DHT::ConvertCelciustoFarenheit(float const celsius)
+{
return celsius * 9 / 5 + 32;
}
-float DHT::ConvertCelciustoKelvin(float celsius) {
+float DHT::ConvertCelciustoKelvin(float const celsius)
+{
return celsius + 273.15;
}
// dewPoint function NOAA
// reference: http://wahiduddin.net/calc/density_algorithms.htm
-float DHT::CalcdewPoint(float celsius, float humidity) {
+float DHT::CalcdewPoint(float const celsius, float const humidity)
+{
float A0= 373.15/(273.15 + celsius);
float SUM = -7.90298 * (A0-1);
SUM += 5.02808 * log10(A0);
@@ -196,16 +187,17 @@
// delta max = 0.6544 wrt dewPoint()
// 5x faster than dewPoint()
// reference: http://en.wikipedia.org/wiki/Dew_point
-float DHT::CalcdewPointFast(float celsius, float humidity)
+float DHT::CalcdewPointFast(float const celsius, float const humidity)
{
- float a = 17.271;
- float b = 237.7;
- float temp = (a * celsius) / (b + celsius) + log(humidity/100);
- float Td = (b * temp) / (a - temp);
- return Td;
+ float a = 17.271;
+ float b = 237.7;
+ float temp = (a * celsius) / (b + celsius) + log(humidity/100);
+ float Td = (b * temp) / (a - temp);
+ return Td;
}
-float DHT::ReadTemperature(eScale Scale) {
+float DHT::ReadTemperature(eScale Scale)
+{
if (Scale == FARENHEIT)
return ConvertCelciustoFarenheit(_lastTemperature);
else if (Scale == KELVIN)
@@ -214,7 +206,8 @@
return _lastTemperature;
}
-float DHT::CalcHumidity() {
+float DHT::CalcHumidity()
+{
int v;
switch (_DHTtype) {