I did some research and found the specification sheet for the LM35 and decided to hook it up to the Arduino. The LM35 outputs a linear voltage of 10 millivolts per degree Celsius. The simple program here sends a message back over the serial port to show the temperature in both Celsius and Fahrenheit. It could also be used to control a fan or sound an alarm. The LM35 costs about $1.75 from either BGmicro.com or Jameco.com.
Sorry for the long comments section in the program. I like to put a lot of notes in my programs so I remember why I did something a particular way when I go back and read the program again weeks later. Especially the conversion factor for the Analog to Digital Conversion input and the LM35.
- Code: Select all
/* Analog Read of LM35 temperature sensor
* --------------------------------------
*
* The Analog to Digital Converter (ADC) converts analog values into a digital approximation
* based on the formula ADC Value = sample * 1024 / reference voltage (+5v). So with a +5 volt
* reference, the digital approximation will = input voltage * 205. (Ex. 2.5v * 205 = 512.5)
*
* The LM35 is a precision linear temperature sensor that supplies 10mv per degree Celsius.
* This means at 15 degrees Celsius, it would produce a reading of .150v or 150 millivolts.
* Putting this value into our ADC conversion ( .15v * 205 = 30.75) we can get a close
* approximation of the Celsius temperature by dividing the digital input count by 2.
*
* If the LM35 were supplied by a different reference voltage (9v or 12v) we would have
* to use a different conversion method. For this circuit, dividing by 2 works well.
*
* The LM25 has three legs and looks like a transistor. The two outside legs are
* +5v and Ground, and the middle leg develops the sample voltage.
* LM35 Sources: BGmicro.com and Jameco.com Search term: LM35 Approx $1.75
*
* /|---> Gnd 18K ohm
* | |-----------+---/\/\/\/-----> Gnd
* \|---> +5v |
* +----------- Analog Input pin 5
*
*/
int inPin = 5; // select the input pin for analog temp value
int inVal; // integer value for input read from sensor
int delayVal = 1000; // delay value to read once a second
void setup() {
Serial.begin(9600); // set up Serial library at 9600 bps
}
void loop() {
inVal = analogRead(inPin); // read the value from the sensor
inVal /= 2; // convert 1024 steps into value referenced to +5 volts
Serial.print(inVal); // print input value
Serial.print(" Celsius, "); // print Celsius label
Serial.print((inVal * 9)/ 5 + 32); // convert Celsius to Fahrenheit
Serial.println(" Fahrenheit"); // print Fahrenheit label
delay(delayVal); // delay the program for the requested time
}
Hope this is useful,
Silver
