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‎DHT22.cpp

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/*
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DHT22.cpp - DHT22 sensor library
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Developed by Ben Adams - 2011
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This library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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This library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with this library; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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Humidity and Temperature Sensor DHT22 info found at
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http://www.sparkfun.com/products/10167
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Version 0.3: 17-Jan-2011 by Ben Adams
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This version reads data
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Needs check sum code added at the end of readData
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Version 0.2: 16-Jan-2011 by Ben Adams
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Changed coding style to match other Arduino libraries.
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This version will not read data either!
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Version 0.1: 10-Jan-2011 by Ben Adams nethoncho AT gmail.com
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First Version is a skeleton. This version will not read data!
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Code adapted from the following sources:
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The Arduino OneWire lib
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http://sheepdogguides.com/arduino/ar3ne1humDHT11.htm
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*/
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#include "DHT22.h"
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#include "pins_arduino.h"
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extern "C" {
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#include "WConstants.h"
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#include <avr/io.h>
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#include <avr/interrupt.h>
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#include <avr/pgmspace.h>
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}
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#define DIRECT_READ(base, mask) (((*(base)) & (mask)) ? 1 : 0)
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#define DIRECT_MODE_INPUT(base, mask) ((*(base+1)) &= ~(mask))
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#define DIRECT_MODE_OUTPUT(base, mask) ((*(base+1)) |= (mask))
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#define DIRECT_WRITE_LOW(base, mask) ((*(base+2)) &= ~(mask))
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//#define DIRECT_WRITE_HIGH(base, mask) ((*(base+2)) |= (mask))
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// This should be 40, but the sensor is adding an extra bit at the start
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#define DHT22_DATA_BIT_COUNT 41
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DHT22::DHT22(uint8_t pin)
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{
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_bitmask = digitalPinToBitMask(pin);
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_baseReg = portInputRegister(digitalPinToPort(pin));
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_lastReadTime = millis();
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_lastHumidity = DHT22_ERROR_VALUE;
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_lastTemperature = DHT22_ERROR_VALUE;
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}
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//
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// Read the 40 bit data stream from the DHT 22
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// Store the results in private member data to be read by public member functions
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//
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DHT22_ERROR_t DHT22::readData()
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{
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uint8_t bitmask = _bitmask;
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volatile uint8_t *reg asm("r30") = _baseReg;
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uint8_t retryCount;
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uint8_t bitTimes[DHT22_DATA_BIT_COUNT];
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int currentHumidity;
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int currentTemperature;
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uint8_t checkSum;
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unsigned long currentTime;
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int i;
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currentHumidity = 0;
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currentTemperature = 0;
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checkSum = 0;
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currentTime = millis();
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for(i = 0; i < DHT22_DATA_BIT_COUNT; i++)
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{
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bitTimes[i] = 0;
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}
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if(currentTime - _lastReadTime < 2000)
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{
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// Caller needs to wait 2 seconds between each call to readData
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return DHT_ERROR_TOOQUICK;
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}
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_lastReadTime = currentTime;
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// Pin needs to start HIGH, wait until it is HIGH with a timeout
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cli();
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DIRECT_MODE_INPUT(reg, bitmask);
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sei();
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retryCount = 0;
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do
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{
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if (retryCount > 125)
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{
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return DHT_BUS_HUNG;
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}
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retryCount++;
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delayMicroseconds(2);
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} while(!DIRECT_READ(reg, bitmask));
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// Send the activate pulse
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cli();
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DIRECT_WRITE_LOW(reg, bitmask);
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DIRECT_MODE_OUTPUT(reg, bitmask); // Output Low
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sei();
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delayMicroseconds(1100); // 1.1 ms
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cli();
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DIRECT_MODE_INPUT(reg, bitmask); // Switch back to input so pin can float
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sei();
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// Find the start of the ACK Pulse
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retryCount = 0;
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do
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{
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if (retryCount > 25) //(Spec is 20 to 40 us, 25*2 == 50 us)
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{
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return DHT_ERROR_NOT_PRESENT;
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}
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retryCount++;
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delayMicroseconds(2);
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} while(!DIRECT_READ(reg, bitmask));
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// Find the end of the ACK Pulse
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retryCount = 0;
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do
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{
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if (retryCount > 50) //(Spec is 80 us, 50*2 == 100 us)
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{
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return DHT_ERROR_ACK_TOO_LONG;
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}
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retryCount++;
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delayMicroseconds(2);
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} while(DIRECT_READ(reg, bitmask));
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// Read the 40 bit data stream
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for(i = 0; i < DHT22_DATA_BIT_COUNT; i++)
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{
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// Find the start of the sync pulse
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retryCount = 0;
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do
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{
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if (retryCount > 35) //(Spec is 50 us, 35*2 == 70 us)
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{
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return DHT_ERROR_SYNC_TIMEOUT;
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}
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retryCount++;
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delayMicroseconds(2);
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} while(!DIRECT_READ(reg, bitmask));
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// Measure the width of the data pulse
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retryCount = 0;
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do
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{
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if (retryCount > 50) //(Spec is 80 us, 50*2 == 100 us)
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{
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return DHT_ERROR_DATA_TIMEOUT;
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}
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retryCount++;
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delayMicroseconds(2);
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} while(DIRECT_READ(reg, bitmask));
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bitTimes[i] = retryCount;
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}
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// Now bitTimes have the number of retries (us *2)
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// that were needed to find the end of each data bit
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// Spec: 0 is 26 to 28 us
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// Spec: 1 is 70 us
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// bitTimes[x] <= 11 is a 0
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// bitTimes[x] > 11 is a 1
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// Note: the bits are offset by one from the data sheet, not sure why
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for(i = 0; i < 16; i++)
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{
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if(bitTimes[i + 1] > 11)
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{
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currentHumidity |= (1 << (15 - i));
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}
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}
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for(i = 0; i < 16; i++)
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{
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if(bitTimes[i + 17] > 11)
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{
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currentTemperature |= (1 << (15 - i));
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}
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}
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for(i = 0; i < 8; i++)
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{
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if(bitTimes[i + 33] > 11)
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{
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checkSum |= (1 << (7 - i));
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}
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}
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_lastHumidity = (float(currentHumidity & 0x7FFF) / 10.0);
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if(currentTemperature & 0x8000)
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{
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// Below zero, non standard way of encoding negative numbers!
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currentTemperature &= 0x7FFF;
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_lastTemperature = (float(currentTemperature) / 10.0) * -1.0;
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}
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else
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{
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_lastTemperature = float(currentTemperature) / 10.0;
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}
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// TODO: Test the checksum and return DHT_ERROR_CHECKSUM if bad
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return DHT_ERROR_NONE;
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}
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float DHT22::getHumidity()
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{
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return _lastHumidity;
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}
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float DHT22::getTemperatureC()
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{
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return _lastTemperature;
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}
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//
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// This is used when the millis clock rolls over to zero
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//
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void DHT22::clockReset()
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{
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_lastReadTime = millis();
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}

‎DHT22.h

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#ifndef _DHT22_H_
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#define _DHT22_H_
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#include <inttypes.h>
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#define DHT22_ERROR_VALUE -99.5
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typedef enum
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{
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DHT_ERROR_NONE = 0,
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DHT_BUS_HUNG,
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DHT_ERROR_NOT_PRESENT,
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DHT_ERROR_ACK_TOO_LONG,
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DHT_ERROR_SYNC_TIMEOUT,
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DHT_ERROR_DATA_TIMEOUT,
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DHT_ERROR_CHECKSUM,
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DHT_ERROR_TOOQUICK
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} DHT22_ERROR_t;
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class DHT22
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{
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private:
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uint8_t _bitmask;
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volatile uint8_t *_baseReg;
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unsigned long _lastReadTime;
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float _lastHumidity;
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float _lastTemperature;
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public:
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DHT22(uint8_t pin);
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DHT22_ERROR_t readData(void);
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float getHumidity();
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float getTemperatureC();
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void clockReset();
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};
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#endif /*_DHT22_H_*/

‎README

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DHT22.cpp - DHT22 sensor library
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Developed by Ben Adams - 2011
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Humidity and Temperature Sensor DHT22 info found at
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http://www.sparkfun.com/products/10167
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7+
Version 0.3: 17-Jan-2011 by Ben Adams
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This version reads data
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Needs check sum code added at the end of readData
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Version 0.2: 16-Jan-2011 by Ben Adams
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Changed coding style to match other Arduino libraries.
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This version will not read data either!
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Version 0.1: 10-Jan-2011 by Ben Adams nethoncho AT gmail.com
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First Version is a skeleton. This version will not read data!
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Code adapted from the following sources:
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The Arduino OneWire lib
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http://sheepdogguides.com/arduino/ar3ne1humDHT11.htm

‎examples/Serial/Serial.pde

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#include <DHT22.h>
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// Data wire is plugged into port 7 on the Arduino
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// Connect a 4.7K resistor between VCC and the data pin (strong pullup)
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#define DHT22_PIN 7
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// Setup a DHT22 instance
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DHT22 myDHT22(DHT22_PIN);
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void setup(void)
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{
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// start serial port
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Serial.begin(9600);
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Serial.println("DHT22 Library Demo");
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}
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void loop(void)
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{
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DHT22_ERROR_t errorCode;
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delay(2000);
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Serial.print("Requesting data...");
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errorCode = myDHT22.readData();
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if(errorCode == DHT_ERROR_NONE)
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{
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Serial.print("Got Data ");
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Serial.print(myDHT22.getTemperatureC());
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Serial.print("C ");
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Serial.print(myDHT22.getHumidity());
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Serial.println("%");
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}
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else
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{
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Serial.print("Error Code ");
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Serial.print(errorCode);
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Serial.println(" readData Failed");
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}
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}

‎keywords.txt

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#######################################
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# Syntax Coloring Map For DHT22
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#######################################
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#######################################
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# Datatypes (KEYWORD1)
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#######################################
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DHT22 KEYWORD1
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#######################################
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# Methods and Functions (KEYWORD2)
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#######################################
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readData KEYWORD2
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getHumidity KEYWORD2
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getTemperatureC KEYWORD2
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clockReset KEYWORD2
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#######################################
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# Instances (KEYWORD2)
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#######################################
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#######################################
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# Constants (LITERAL1)
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#######################################

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