This tutorial will show you how to take temperature readings using the Freetronics temperature sensor and an Arduino Uno.

Transcription

1 This tutorial will show you how to take temperature readings using the Freetronics temperature sensor and an Arduino Uno. Note that there are two different module types: the temperature sensor module and the humidity & temperature sensor module. If you have the humidity & temperature sensor module you will need to download a library for the Arduino IDE and use different wiring and code follow the instructions for that module here: humidity- temperature- sensor- module- quickstart- guide Parts required Here is what you will need: Arduino Uno board Temperature Sensor Module Breadboard 3 male- to- male jumper wires Arduino IDE software (free at USB cable Wire it up! Attach the temperature sensor module to your breadboard. The GND pin should connect the GND pin on the Arduino board, the VCC pin should connect the 5V pin on the Arduino board, and the DATA pin should connect to the digital I/O pin 2 on the Arduino board all these are connected via the breadboard using male- to- male jumper wires. The pictures on the next page show how to wire it all up in greater detail.

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3 Arduino code Here is the code for the Arduino sketch (you can also copy it from temperature- sensor- module- quickstart- guide). Make sure you scroll down to see how to test the sensor. #define REF_PIN 2 void getcurrenttemp( int *sign, int *whole, int *fract); char temp_string[10]; void setup() Serial.begin(9600); // initialize DS18B20 datapin digitalwrite(ref_pin, LOW); pinmode(ref_pin, INPUT); // sets the digital pin as input (logic 1) pinmode(15, INPUT); void loop() getcurrenttemp(temp_string); Serial.println(temp_string); delay(1000); void OneWireReset (int Pin) // reset. Should improve to act as a presence pulse // bring low for 500 us delaymicroseconds (500); delaymicroseconds (500); void OneWireOutByte (int Pin, byte d) // output byte d (least sig bit first). byte n; for (n=8; n!=0; n- - ) if ((d & 0x01) == 1) // test least sig bit

4 delaymicroseconds (5); delaymicroseconds (60); else delaymicroseconds (60); d = d>>1; // now the next bit is in the least sig bit position. byte OneWireInByte (int Pin) // read byte, least sig byte first byte d, n, b; for (n=0; n<8; n++) delaymicroseconds (5); delaymicroseconds (5); b = digitalread (Pin); delaymicroseconds (50); d = (d >> 1) (b<<7); // shift d to right and insert b in most sig bit position return (d);

5 void getcurrenttemp (char *temp) int HighByte, LowByte, TReading, Tc_100, sign, whole, fract; OneWireReset (REF_PIN); OneWireOutByte (REF_PIN, 0xcc); OneWireOutByte (REF_PIN, 0x44); // perform temperature conversion, strong pullup for one sec OneWireReset (REF_PIN); OneWireOutByte (REF_PIN, 0xcc); OneWireOutByte (REF_PIN, 0xbe); LowByte = OneWireInByte (REF_PIN); HighByte = OneWireInByte (REF_PIN); TReading = (HighByte << 8) + LowByte; sign = TReading & 0x8000; // test most sig bit if (sign) // negative TReading = (TReading ^ 0xffff) + 1; // 2's comp Tc_100 = (6 * TReading) + TReading / 4; // multiply by (100 * ) or 6.25 whole = Tc_100 / 100; // separate off the whole and fractional portions fract = Tc_100 % 100; if (sign) temp[0] = '- '; else temp[0] = '+'; if (whole/100 == 0) temp[1] = ' '; else temp[1] = whole/100+'0'; temp[2] = (whole- (whole/100)*100)/10 +'0' ;

6 temp[3] = whole- (whole/10)*10 +'0'; temp[4] = '.'; temp[5] = fract/10 +'0'; temp[6] = fract- (fract/10)*10 +'0'; temp[7] = '\0'; Testing Upload the code once you connect the Arduino to the computer with a USB cable. In the Arduino IDE, click on Tools > Serial Monitor. Make sure you change the baud rate to 9600 baud. The temperature sensor should have a constant blue light and the Serial Monitor should display the temperature readings every second. Think about how you could use the temperature sensor. You can connect the Arduino to a dot- matrix or LCD display to display the temperature. It could also be used for climate control inside a room. How else could you use it?