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DHT22/RHT03 Humidity/Temperature Sensor and 4 Character Display, My Second Arduino Project

November 14, 2012 10:10 pm

So I’ve been working on learning about the SoC called Arduino, to do so I’ve been using the book, Environmental Monitoring with Arduino, by Emily Gertz and Patrick Di Justo; published by O’Reilly Press. This project is designed to help you learn how to work with and program sensors. The sensor used here is the DHT22/RHT03 from adafruit. To date the project has not been going that well. Being that I’m not a programmer to start is my first hurdle and being new to electronics is my second. So I’m having real fun here. The set up seemed simple with the exception of the description of where and how the 4.7K resistor was to be placed, that could have be illustrated better.

Presently I’m getting the following problem:

6Error Cheksum6Error Cheksum6Error Cheksum6Error Cheksum6Error Cheksum6Error Cheksum6Error Cheksum6Error Cheksum6Error Cheksum6Error Cheksum6Error Cheksum6Error Cheksum6Error Cheksum46Error Cheksum6Error Cheksum6Error Cheksum6Error Cheksum6Error Cheksum6Error Cheksum6Error Cheksum6Error Cheksum6Error Cheksum6Error Cheksum6Error Cheksum6Error Cheksum6Error Cheksum6Error Cheksum6Error Cheksum46Error Cheksum6Error Cheksum6Error Cheksum6Error Cheksum6Error Cheksum6Error Cheksum6Error Cheksum0Temperature: -3276.70C Humidity: 3263.80%
-1086.55d

As you can see we have all those cheksum errors and then there is the whole problem of incorrect humidity and temperature readings and the fact that nothing useful is showing up on the 4 character display.

Hopefully my local Maker friends will have a solution for me.

The following is the code taken from the Environmental Monitoring with Arduino book;
/* Temperature-Humidity-Dewpoint Monitor
This sketch gathers temperature and humidity data via a DHT22 sensor,
and also calculates dew point based on those measurements.
*/

#include
#include

#define DHT22_ERROR_VALUE -99.5

#define DHT22_PIN 4

typedef enum
{
DHT_ERROR_NONE = 0,
DHT_BUS_HUNG,
DHT_ERROR_NOT_PRESENT,
DHT_ERROR_ACK_TOO_LONG,
DHT_ERROR_SYNC_TIMEOUT,
DHT_ERROR_DATA_TIMEOUT,
DHT_ERROR_CHECKSUM,
DHT_ERROR_TOOQUICK
} DHT22_ERROR_t;

class DHT22
{
private:
uint8_t _bitmask;
volatile uint8_t *_baseReg;
unsigned long _lastReadTime;
float _lastHumidity;
float _lastTemperature;

public:
DHT22(uint8_t pin);
DHT22_ERROR_t readData(void);
float getHumidity();
float getTemperatureC();
void clockReset();
};

// Setup a DHT22 instance
DHT22 myDHT22(DHT22_PIN);

#define SerialIn 2
#define SerialOut 3

#define WDelay 900

byte thou=0;
byte hund=0;
byte tens=0;
byte ones=0;

SoftwareSerial mySerialPort(SerialIn, SerialOut);

void setup(void)
{

// start serial port
Serial.begin(9600);
Serial.println(“DHT22 Library Demo”);

pinMode(SerialOut, OUTPUT);
pinMode(SerialIn, INPUT);

mySerialPort.begin(9600);
mySerialPort.print(“v”);

mySerialPort.print(“xxxx”);
delay(WDelay);
mySerialPort.print(“—-”);
delay(WDelay);
mySerialPort.print(“8888″);
delay(WDelay);
mySerialPort.print(“xxxx”);
delay(WDelay);

}

void loop(void)
{
float tempC;
float tempF;
float humid;
float dewPoint;

DHT22_ERROR_t errorCode;

delay(2000);

errorCode = myDHT22.readData();

Serial.print(errorCode);

switch(errorCode)
{
case DHT_ERROR_NONE:
Serial.print(“Temperature: “);
tempC = myDHT22.getTemperatureC();

Serial.print(tempC);
Serial.print(“C Humidity: “);

dispData((int)tempC, ‘C’);

tempF = (tempC*1.8)+32;

delay(WDelay);
dispData((int) tempF, ‘F’);
delay(WDelay);

humid = myDHT22.getHumidity();

Serial.print(humid);
Serial.println(“%”);

dispData((int)humid, ‘h’);
delay(WDelay);

dewPoint = calculateDewpoint(tempC, humid);
dispData((int) dewPoint, ‘d’);

Serial.print(dewPoint);
Serial.println(“d”);

delay(WDelay);

break;
case DHT_ERROR_CHECKSUM:
Serial.print(“Error Cheksum”);
break;
case DHT_BUS_HUNG:
Serial.print(“Bus Hung”);
break;
case DHT_ERROR_NOT_PRESENT:
Serial.print(“Not Present”);
break;
case DHT_ERROR_ACK_TOO_LONG:
break;
case DHT_ERROR_SYNC_TIMEOUT:
break;
case DHT_ERROR_DATA_TIMEOUT:
break;
case DHT_ERROR_TOOQUICK:
break;
}

}

float calculateDewpoint(float T, float RH)
{
// approximate dewpoint using the formula from wikipedia’s article on dewpoint

float dp = 0.0;
float gTRH = 0.0;
float a = 17.271;
float b = 237.7;

gTRH = ((a*T)/(b+T))+log(RH/100);
dp = (b*gTRH)/(a-gTRH);

return dp;
}

void dispData(int i, char c)
{

if(c == ‘k’ || c==’K’ || c==’m’ || c==’l’ || c == ‘v’ || c==’V’ || c==’W’ || c==’Z’ || c==’w’ || c==’z')
{
mySerialPort.print(“bAdx”);
return;

}

if((i< -999) || (i>9999))
{
mySerialPort.print(“ERRx”);
return;
}

mySerialPort.print(“v”);

if (i > 999) { // i between 1000 and 9999 inclusive

mySerialPort.print(i, DEC);

} else if (i > 99) { // i between 100 and 999, inclusive

mySerialPort.print(i, DEC);
mySerialPort.print(c);

} else if (i > 9) { // i between 10 and 99 inclusive

mySerialPort.print(i, DEC);
mySerialPort.print(“x”);
mySerialPort.print(c);

} else if (i > 0) { // i between 1 and 9 inclusive

mySerialPort.print(“x”);
mySerialPort.print(i, DEC);
mySerialPort.print(“x”);
mySerialPort.print(c);

} else if (i < -99) { // i between -100 and -999, inclusive

mySerialPort.print(i, DEC);
mySerialPort.print(c);

} else if (i < -9) { // i between -10 and -99, inclusive

mySerialPort.print(i, DEC);
mySerialPort.print(c);

} else if (i < 0) { // i between -1 and -9 inclusive

mySerialPort.print(i, DEC);
mySerialPort.print("x");
mySerialPort.print(c);

}

}

/*
DHT22.cpp - DHT22 sensor library
Developed by Ben Adams - 2011

This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA

Humidity and Temperature Sensor DHT22 info found at

http://www.sparkfun.com/products/10167

Version 0.4: 24-Jan-2011 by Ben Adams
Added return code constants to keywords.txt
Returns DHT_ERROR_CHECKSUM on check sum mismatch

Version 0.3: 17-Jan-2011 by Ben Adams
This version reads data
Needs check sum code added at the end of readData

Version 0.2: 16-Jan-2011 by Ben Adams
Changed coding style to match other Arduino libraries.
This version will not read data either!

Version 0.1: 10-Jan-2011 by Ben Adams nethoncho AT gmail.com
First Version is a skeleton. This version will not read data!
Code adapted from the following sources:
The Arduino OneWire lib

http://sheepdogguides.com/arduino/ar3ne1humDHT11.htm

*/

#include "Arduino.h"

extern "C" {
//#include "WConstants.h"
#include
#include
#include

}

#define DIRECT_READ(base, mask) (((*(base)) & (mask)) ? 1 : 0)
#define DIRECT_MODE_INPUT(base, mask) ((*(base+1)) &= ~(mask))
#define DIRECT_MODE_OUTPUT(base, mask) ((*(base+1)) |= (mask))
#define DIRECT_WRITE_LOW(base, mask) ((*(base+2)) &= ~(mask))
//#define DIRECT_WRITE_HIGH(base, mask) ((*(base+2)) |= (mask))

// This should be 40, but the sensor is adding an extra bit at the start
#define DHT22_DATA_BIT_COUNT 41

DHT22::DHT22(uint8_t pin)
{
_bitmask = digitalPinToBitMask(pin);
_baseReg = portInputRegister(digitalPinToPort(pin));
_lastReadTime = millis();
_lastHumidity = DHT22_ERROR_VALUE;
_lastTemperature = DHT22_ERROR_VALUE;
}

//
// Read the 40 bit data stream from the DHT 22
// Store the results in private member data to be read by public member functions
//
DHT22_ERROR_t DHT22::readData()
{
uint8_t bitmask = _bitmask;
volatile uint8_t *reg asm(“r30″) = _baseReg;
uint8_t retryCount;
uint8_t bitTimes[DHT22_DATA_BIT_COUNT];
int currentHumidity;
int currentTemperature;
uint8_t checkSum, csPart1, csPart2, csPart3, csPart4;
unsigned long currentTime;
int i;

currentHumidity = 0;
currentTemperature = 0;
checkSum = 0;
currentTime = millis();
for(i = 0; i < DHT22_DATA_BIT_COUNT; i++)
{
bitTimes[i] = 0;
}

if(currentTime - _lastReadTime < 2000)
{
// Caller needs to wait 2 seconds between each call to readData
return DHT_ERROR_TOOQUICK;
}
_lastReadTime = currentTime;

// Pin needs to start HIGH, wait until it is HIGH with a timeout
cli();
DIRECT_MODE_INPUT(reg, bitmask);
sei();
retryCount = 0;
do
{
if (retryCount > 125)
{
return DHT_BUS_HUNG;
}
retryCount++;
delayMicroseconds(2);
} while(!DIRECT_READ(reg, bitmask));
// Send the activate pulse
cli();
DIRECT_WRITE_LOW(reg, bitmask);
DIRECT_MODE_OUTPUT(reg, bitmask); // Output Low
sei();
delayMicroseconds(1100); // 1.1 ms
cli();
DIRECT_MODE_INPUT(reg, bitmask); // Switch back to input so pin can float
sei();
// Find the start of the ACK Pulse
retryCount = 0;
do
{
if (retryCount > 25) //(Spec is 20 to 40 us, 25*2 == 50 us)
{
return DHT_ERROR_NOT_PRESENT;
}
retryCount++;
delayMicroseconds(2);
} while(!DIRECT_READ(reg, bitmask));
// Find the end of the ACK Pulse
retryCount = 0;
do
{
if (retryCount > 50) //(Spec is 80 us, 50*2 == 100 us)
{
return DHT_ERROR_ACK_TOO_LONG;
}
retryCount++;
delayMicroseconds(2);
} while(DIRECT_READ(reg, bitmask));
// Read the 40 bit data stream
for(i = 0; i < DHT22_DATA_BIT_COUNT; i++)
{
// Find the start of the sync pulse
retryCount = 0;
do
{
if (retryCount > 35) //(Spec is 50 us, 35*2 == 70 us)
{
return DHT_ERROR_SYNC_TIMEOUT;
}
retryCount++;
delayMicroseconds(2);
} while(!DIRECT_READ(reg, bitmask));
// Measure the width of the data pulse
retryCount = 0;
do
{
if (retryCount > 50) //(Spec is 80 us, 50*2 == 100 us)
{
return DHT_ERROR_DATA_TIMEOUT;
}
retryCount++;
delayMicroseconds(2);
} while(DIRECT_READ(reg, bitmask));
bitTimes[i] = retryCount;
}
// Now bitTimes have the number of retries (us *2)
// that were needed to find the end of each data bit
// Spec: 0 is 26 to 28 us
// Spec: 1 is 70 us
// bitTimes[x] < = 11 is a 0
// bitTimes[x] > 11 is a 1
// Note: the bits are offset by one from the data sheet, not sure why
for(i = 0; i < 16; i++)
{
if(bitTimes[i + 1] > 11)
{
currentHumidity |= (1 < < (15 - i));
}
}
for(i = 0; i < 16; i++)
{
if(bitTimes[i + 17] > 11)
{
currentTemperature |= (1 < < (15 - i));
}
}
for(i = 0; i < 8; i++)
{
if(bitTimes[i + 33] > 11)
{
checkSum |= (1 < < (7 - i));
}
}

_lastHumidity = (float(currentHumidity & 0x7FFF) / 10.0);
if(currentTemperature & 0x8000)
{
// Below zero, non standard way of encoding negative numbers!
currentTemperature &= 0x7FFF;
_lastTemperature = (float(currentTemperature) / 10.0) * -1.0;
}
else
{
_lastTemperature = float(currentTemperature) / 10.0;
}

csPart1 = currentHumidity >> 8;
csPart2 = currentHumidity & 0xFF;
csPart3 = currentTemperature >> 8;
csPart4 = currentTemperature & 0xFF;
if(checkSum == ((csPart1 + csPart2 + csPart3 + csPart4) & 0xFF))
{
return DHT_ERROR_NONE;
}
return DHT_ERROR_CHECKSUM;
}

float DHT22::getHumidity()
{
return _lastHumidity;
}

float DHT22::getTemperatureC()
{
return _lastTemperature;
}

//
// This is used when the millis clock rolls over to zero
//
void DHT22::clockReset()
{
_lastReadTime = millis();

}

Hubble Sees Violent Star Formation Episodes in Dwarf Galaxies

October 27, 2012 6:20 pm

The NASA/ESA Hubble Space Telescope has imaged the faint irregular galaxy NGC 3738, a starburst galaxy. The galaxy is in the midst of a violent episode of star formation, during which it is converting reservoirs of hydrogen gas located in the galaxy’s center into stars. Hubble spots this gas glowing red around NGC 3738, one of the most distinctive signs of ongoing star formation.

READ MORE

Source: Science Daily