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Refactor algorithm to dynamically adjust to faster/slower processors. Fix #35 #30.

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This commit is contained in:
Tony DiCola 2015-06-26 15:14:17 -07:00
parent a67e1a7e06
commit 9d7a9da8ae
4 changed files with 196 additions and 141 deletions
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209
DHT.cpp
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@ -1,4 +1,4 @@
/* DHT library
/* DHT library
MIT license
written by Adafruit Industries
@ -9,8 +9,9 @@ written by Adafruit Industries
DHT::DHT(uint8_t pin, uint8_t type, uint8_t count) {
_pin = pin;
_type = type;
_count = count;
firstreading = true;
_firstreading = true;
// Note that count is now ignored as the DHT reading algorithm adjusts itself
// basd on the speed of the processor.
}
void DHT::begin(void) {
@ -22,158 +23,198 @@ void DHT::begin(void) {
//boolean S == Scale. True == Farenheit; False == Celcius
float DHT::readTemperature(bool S) {
float f;
float f = NAN;
if (read()) {
switch (_type) {
case DHT11:
f = data[2];
if(S)
f = convertCtoF(f);
return f;
if(S) {
f = convertCtoF(f);
}
break;
case DHT22:
case DHT21:
f = data[2] & 0x7F;
f *= 256;
f += data[3];
f /= 10;
if (data[2] & 0x80)
f *= -1;
if(S)
f = convertCtoF(f);
return f;
if (data[2] & 0x80) {
f *= -1;
}
if(S) {
f = convertCtoF(f);
}
break;
}
}
return NAN;
return f;
}
float DHT::convertCtoF(float c) {
return c * 9 / 5 + 32;
return c * 9 / 5 + 32;
}
float DHT::convertFtoC(float f) {
return (f - 32) * 5 / 9;
return (f - 32) * 5 / 9;
}
float DHT::readHumidity(void) {
float f;
float f = NAN;
if (read()) {
switch (_type) {
case DHT11:
f = data[0];
return f;
break;
case DHT22:
case DHT21:
f = data[0];
f *= 256;
f += data[1];
f /= 10;
return f;
break;
}
}
return NAN;
return f;
}
float DHT::computeHeatIndex(float tempFahrenheit, float percentHumidity) {
// Adapted from equation at: https://github.com/adafruit/DHT-sensor-library/issues/9 and
// Wikipedia: http://en.wikipedia.org/wiki/Heat_index
return -42.379 +
2.04901523 * tempFahrenheit +
return -42.379 +
2.04901523 * tempFahrenheit +
10.14333127 * percentHumidity +
-0.22475541 * tempFahrenheit*percentHumidity +
-0.00683783 * pow(tempFahrenheit, 2) +
-0.05481717 * pow(percentHumidity, 2) +
0.00122874 * pow(tempFahrenheit, 2) * percentHumidity +
-0.05481717 * pow(percentHumidity, 2) +
0.00122874 * pow(tempFahrenheit, 2) * percentHumidity +
0.00085282 * tempFahrenheit*pow(percentHumidity, 2) +
-0.00000199 * pow(tempFahrenheit, 2) * pow(percentHumidity, 2);
}
boolean DHT::read(void) {
uint8_t laststate = HIGH;
uint8_t counter = 0;
uint8_t j = 0, i;
unsigned long currenttime;
// Check if sensor was read less than two seconds ago and return early
// to use last reading.
currenttime = millis();
uint32_t currenttime = millis();
if (currenttime < _lastreadtime) {
// ie there was a rollover
_lastreadtime = 0;
}
if (!firstreading && ((currenttime - _lastreadtime) < 2000)) {
return true; // return last correct measurement
//delay(2000 - (currenttime - _lastreadtime));
if (!_firstreading && ((currenttime - _lastreadtime) < 2000)) {
return _lastresult; // return last correct measurement
}
firstreading = false;
/*
Serial.print("Currtime: "); Serial.print(currenttime);
Serial.print(" Lasttime: "); Serial.print(_lastreadtime);
*/
_firstreading = false;
_lastreadtime = millis();
// Reset 40 bits of received data to zero.
data[0] = data[1] = data[2] = data[3] = data[4] = 0;
// pull the pin high and wait 250 milliseconds
// Send start signal. See DHT datasheet for full signal diagram:
// http://www.adafruit.com/datasheets/Digital%20humidity%20and%20temperature%20sensor%20AM2302.pdf
// Go into high impedence state to let pull-up raise data line level and
// start the reading process.
digitalWrite(_pin, HIGH);
delay(250);
// now pull it low for ~20 milliseconds
// First set data line low for 20 milliseconds.
pinMode(_pin, OUTPUT);
digitalWrite(_pin, LOW);
delay(20);
// Turn off interrupts temporarily because the next sections are timing critical
// and we don't want any interruptions.
noInterrupts();
// End the start signal by setting data line high for 40 microseconds.
digitalWrite(_pin, HIGH);
delayMicroseconds(40);
// Now start reading the data line to get the value from the DHT sensor.
pinMode(_pin, INPUT);
delayMicroseconds(10); // Delay a bit to let sensor pull data line low.
// read in timings
for ( i=0; i< MAXTIMINGS; i++) {
counter = 0;
while (digitalRead(_pin) == laststate) {
counter++;
delayMicroseconds(1);
if (counter == 255) {
break;
}
}
laststate = digitalRead(_pin);
if (counter == 255) break;
// ignore first 3 transitions
if ((i >= 4) && (i%2 == 0)) {
// shove each bit into the storage bytes
data[j/8] <<= 1;
if (counter > _count)
data[j/8] |= 1;
j++;
}
// First expect a low signal for ~80 microseconds followed by a high signal
// for ~80 microseconds again.
if (expectPulse(LOW) == 0) {
DEBUG_PRINTLN(F("Timeout waiting for start signal low pulse."));
_lastresult = false;
return _lastresult;
}
if (expectPulse(HIGH) == 0) {
DEBUG_PRINTLN(F("Timeout waiting for start signal high pulse."));
_lastresult = false;
return _lastresult;
}
// Now read the 40 bits sent by the sensor. Each bit is sent as a 50
// microsecond low pulse followed by a variable length high pulse. If the
// high pulse is ~28 microseconds then it's a 0 and if it's ~70 microseconds
// then it's a 1. We measure the cycle count of the initial 50us low pulse
// and use that to compare to the cycle count of the high pulse to determine
// if the bit is a 0 (high state cycle count < low state cycle count), or a
// 1 (high state cycle count > low state cycle count).
for (int i=0; i<40; ++i) {
uint32_t lowCycles = expectPulse(LOW);
if (lowCycles == 0) {
DEBUG_PRINTLN(F("Timeout waiting for bit low pulse."));
_lastresult = false;
return _lastresult;
}
uint32_t highCycles = expectPulse(HIGH);
if (highCycles == 0) {
DEBUG_PRINTLN(F("Timeout waiting for bit high pulse."));
_lastresult = false;
return _lastresult;
}
data[i/8] <<= 1;
// Now compare the low and high cycle times to see if the bit is a 0 or 1.
if (highCycles > lowCycles) {
// High cycles are greater than 50us low cycle count, must be a 1.
data[i/8] |= 1;
}
// Else high cycles are less than (or equal to, a weird case) the 50us low
// cycle count so this must be a zero. Nothing needs to be changed in the
// stored data.
}
// Re-enable interrupts, timing critical code is complete.
interrupts();
/*
Serial.println(j, DEC);
Serial.print(data[0], HEX); Serial.print(", ");
Serial.print(data[1], HEX); Serial.print(", ");
Serial.print(data[2], HEX); Serial.print(", ");
Serial.print(data[3], HEX); Serial.print(", ");
Serial.print(data[4], HEX); Serial.print(" =? ");
Serial.println(data[0] + data[1] + data[2] + data[3], HEX);
*/
// check we read 40 bits and that the checksum matches
if ((j >= 40) &&
(data[4] == ((data[0] + data[1] + data[2] + data[3]) & 0xFF)) ) {
return true;
DEBUG_PRINTLN(F("Received:"));
DEBUG_PRINT(data[0], HEX); DEBUG_PRINT(F(", "));
DEBUG_PRINT(data[1], HEX); DEBUG_PRINT(F(", "));
DEBUG_PRINT(data[2], HEX); DEBUG_PRINT(F(", "));
DEBUG_PRINT(data[3], HEX); DEBUG_PRINT(F(", "));
DEBUG_PRINT(data[4], HEX); DEBUG_PRINT(F(" =? "));
DEBUG_PRINTLN(data[0] + data[1] + data[2] + data[3], HEX);
// Check we read 40 bits and that the checksum matches.
if (data[4] == ((data[0] + data[1] + data[2] + data[3]) & 0xFF)) {
_lastresult = true;
return _lastresult;
}
else {
DEBUG_PRINTLN(F("Checksum failure!"));
_lastresult = false;
return _lastresult;
}
return false;
}
// Expect the signal line to be at the specified level for a period of time and
// return a count of loop cycles spent at that level (this cycle count can be
// used to compare the relative time of two pulses). If more than a millisecond
// ellapses without the level changing then the call fails with a 0 response.
uint32_t DHT::expectPulse(bool level) {
uint32_t count = 0;
uint32_t end = micros() + 1000;
// Loop while counting cycles until the level changes.
while (digitalRead(_pin) == level) {
count++;
if (micros() >= end) {
// Exceeded timeout waiting for level to change, fail.
return 0;
}
}
return count;
}

101
DHT.h
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@ -1,41 +1,60 @@
#ifndef DHT_H
#define DHT_H
#if ARDUINO >= 100
#include "Arduino.h"
#else
#include "WProgram.h"
#endif
/* DHT library
MIT license
written by Adafruit Industries
*/
// how many timing transitions we need to keep track of. 2 * number bits + extra
#define MAXTIMINGS 85
#define DHT11 11
#define DHT22 22
#define DHT21 21
#define AM2301 21
class DHT {
private:
uint8_t data[6];
uint8_t _pin, _type, _count;
unsigned long _lastreadtime;
boolean firstreading;
public:
DHT(uint8_t pin, uint8_t type, uint8_t count=6);
void begin(void);
float readTemperature(bool S=false);
float convertCtoF(float);
float convertFtoC(float);
float computeHeatIndex(float tempFahrenheit, float percentHumidity);
float readHumidity(void);
boolean read(void);
};
#endif
/* DHT library
MIT license
written by Adafruit Industries
*/
#ifndef DHT_H
#define DHT_H
#if ARDUINO >= 100
#include "Arduino.h"
#else
#include "WProgram.h"
#endif
// Uncomment to enable printing out nice debug messages.
//#define DHT_DEBUG
// Define where debug output will be printed.
#define DEBUG_PRINTER Serial
// Setup debug printing macros.
#ifdef DHT_DEBUG
#define DEBUG_PRINT(...) { DEBUG_PRINTER.print(__VA_ARGS__); }
#define DEBUG_PRINTLN(...) { DEBUG_PRINTER.println(__VA_ARGS__); }
#else
#define DEBUG_PRINT(...) {}
#define DEBUG_PRINTLN(...) {}
#endif
// Define types of sensors.
#define DHT11 11
#define DHT22 22
#define DHT21 21
#define AM2301 21
class DHT {
public:
DHT(uint8_t pin, uint8_t type, uint8_t count=6);
void begin(void);
float readTemperature(bool S=false);
float convertCtoF(float);
float convertFtoC(float);
float computeHeatIndex(float tempFahrenheit, float percentHumidity);
float readHumidity(void);
boolean read(void);
private:
uint8_t data[6];
uint8_t _pin, _type;
uint32_t _lastreadtime;
bool _firstreading;
bool _lastresult;
uint32_t expectPulse(bool level);
};
#endif

25
examples/DHTtester/DHTtester.ino
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@ -6,7 +6,7 @@
#define DHTPIN 2 // what pin we're connected to
// Uncomment whatever type you're using!
//#define DHTTYPE DHT11 // DHT 11
//#define DHTTYPE DHT11 // DHT 11
#define DHTTYPE DHT22 // DHT 22 (AM2302)
//#define DHTTYPE DHT21 // DHT 21 (AM2301)
@ -17,21 +17,16 @@
// Connect pin 4 (on the right) of the sensor to GROUND
// Connect a 10K resistor from pin 2 (data) to pin 1 (power) of the sensor
// Initialize DHT sensor for normal 16mhz Arduino
// Initialize DHT sensor.
// Note that older versions of this library took an optional third parameter to
// tweak the timings for faster processors. This parameter is no longer needed
// as the current DHT reading algorithm adjusts itself to work on faster procs.
DHT dht(DHTPIN, DHTTYPE);
// NOTE: For working with a faster chip, like an Arduino Due or Teensy, you
// might need to increase the threshold for cycle counts considered a 1 or 0.
// You can do this by passing a 3rd parameter for this threshold. It's a bit
// of fiddling to find the right value, but in general the faster the CPU the
// higher the value. The default for a 16mhz AVR is a value of 6. For an
// Arduino Due that runs at 84mhz a value of 30 works.
// Example to initialize DHT sensor for Arduino Due:
//DHT dht(DHTPIN, DHTTYPE, 30);
void setup() {
Serial.begin(9600);
Serial.begin(9600);
Serial.println("DHTxx test!");
dht.begin();
}
@ -46,7 +41,7 @@ void loop() {
float t = dht.readTemperature();
// Read temperature as Fahrenheit
float f = dht.readTemperature(true);
// Check if any reads failed and exit early (to try again).
if (isnan(h) || isnan(t) || isnan(f)) {
Serial.println("Failed to read from DHT sensor!");
@ -57,10 +52,10 @@ void loop() {
// Must send in temp in Fahrenheit!
float hi = dht.computeHeatIndex(f, h);
Serial.print("Humidity: ");
Serial.print("Humidity: ");
Serial.print(h);
Serial.print(" %\t");
Serial.print("Temperature: ");
Serial.print("Temperature: ");
Serial.print(t);
Serial.print(" *C ");
Serial.print(f);

2
library.properties
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@ -1,5 +1,5 @@
name=DHT sensor library
version=1.0.0
version=1.1.0
author=Adafruit
maintainer=Adafruit <info@adafruit.com>
sentence=Arduino library for DHT11, DHT22, etc Temp & Humidity Sensors