I understood it had to do with the CLI() function and it's partner sei() and timing the RHT03 needs that stops some important internal clocks.
cli(); //------------------------------------ disable global interrupts {see DHT.cpp}
sei(); //------------------------------------------------ enable interrupts
I cant find it right now but those two functions were explained in the Arduino Cookbook Second Edition.
If I understood things right these two functions also will give I2C an headache too, if they are used when a I2C call is being processed.
The way it was explained to me was you don't want to read both at the same time. I know. I was scratching my head at that one too. There is an example in Arduino Cook Book 2nd Edition where it showed how to talk to one serial object at a time. (Great bed time story- just hard to remember where locate the information)
DHTtester.pde >>
Code: Select all// DHTtester.pde FILE
// Example testing sketch for various DHT humidity/temperature sensors
// Written by ladyada, public domain
#include "DHT.h"
#define DHTPIN 2 // what pin we're connected to
// Uncomment whatever type you're using!
//#define DHTTYPE DHT11 // DHT 11
#define DHTTYPE DHT22 // DHT 22 (AM2302)
//#define DHTTYPE DHT21 // DHT 21 (AM2301)
// Connect pin 1 (on the left) of the sensor to +5V
// Connect pin 2 of the sensor to whatever your DHTPIN is
// 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
DHT dht(DHTPIN, DHTTYPE);
void setup() {
Serial.begin(9600);
Serial.println("DHTxx test!");
dht.begin();
}
void loop() {
// Reading temperature or humidity takes about 250 milliseconds!
// Sensor readings may also be up to 2 seconds 'old' (its a very slow sensor)
float h = dht.readHumidity();
float t = dht.readTemperature();
// check if returns are valid, if they are NaN (not a number) then something went wrong!
if (isnan(t) || isnan(h)) {
Serial.println("Failed to read from DHT");
} else {
Serial.print("Humidity: ");
Serial.print(h);
Serial.print(" %\t");
Serial.print("Temperature: ");
Serial.print(t);
Serial.println(" *C");
}
}
DHT.h >>
Code: Select all//HDT.h File
#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;
boolean read(void);
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 readHumidity(void);
};
#endif
DHT.cpp >>
Code: Select all/* DHT.cpp library
MIT license
written by Adafruit Industries
*/
#include "DHT.h"
DHT::DHT(uint8_t pin, uint8_t type, uint8_t count) {
_pin = pin;
_type = type;
_count = count;
firstreading = true;
}
void DHT::begin(void) {
// set up the pins!
pinMode(_pin, INPUT);
digitalWrite(_pin, HIGH);
_lastreadtime = 0;
}
//boolean S == Scale. True == Farenheit; False == Celcius
float DHT::readTemperature(bool S) {
float f;
if (read()) {
switch (_type) {
case DHT11:
f = data[2];
if(S)
f = convertCtoF(f);
return f;
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;
}
}
Serial.print("Read fail");
return NAN;
}
float DHT::convertCtoF(float c) {
return c * 9 / 5 + 32;
}
float DHT::readHumidity(void) {
float f;
if (read()) {
switch (_type) {
case DHT11:
f = data[0];
return f;
case DHT22:
case DHT21:
f = data[0];
f *= 256;
f += data[1];
f /= 10;
return f;
}
}
Serial.print("Read fail");
return NAN;
}
boolean DHT::read(void) {
uint8_t laststate = HIGH;
uint8_t counter = 0;
uint8_t j = 0, i;
unsigned long currenttime;
// pull the pin high and wait 250 milliseconds
digitalWrite(_pin, HIGH);
delay(250);
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));
}
firstreading = false;
/*
Serial.print("Currtime: "); Serial.print(currenttime);
Serial.print(" Lasttime: "); Serial.print(_lastreadtime);
*/
_lastreadtime = millis();
data[0] = data[1] = data[2] = data[3] = data[4] = 0;
// now pull it low for ~20 milliseconds
pinMode(_pin, OUTPUT);
digitalWrite(_pin, LOW);
delay(20);
cli(); //------------------------------------ disable global interrupts
digitalWrite(_pin, HIGH);
delayMicroseconds(40);
pinMode(_pin, INPUT);
// 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++;
}
}
sei(); //------------------------------------------------ enable 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;
}
return false;
}
