Code for April Electric Imp board - temp logger using a TMP36 from adafruit

april_temp_sensor

hardware.pin1.configure(ANALOG_IN);

// LED pin config
hardware.pin2.configure(DIGITAL_OUT_OD_PULLUP);
// initially set to off
hardware.pin2.write(0);

/*
  If you don't have a Hannah board but want to try the
  Cosm.com temperature logging exercise, here it is!
  
  temperature sensor used is tmp36 from adafruit.com for $2.00
  http://learn.adafruit.com/tmp36-temperature-sensor
  temp range -40°C to 150°C / -40°F to 302°F
*/
local output = OutputPort("temp","number");
local postInit = false;
local oldTemp = null;
local reading = null;
local ratio = null;
local voltage = null;
local temperatureC = null;
local temperatureF = null;
local temp = null;

function update_temp() {
  // keep the imp awake
  imp.wakeup(10, update_temp);
  
  // get the raw voltage value from temp sensor btw 0-65535
  // in this case that needs mapping to the range 0-3.3v
  reading = hardware.pin1.read();
  
  // get the ratio 
  ratio = 65535.0 / reading;
  
  // make units milivolts and get voltage we can work with
  //voltage = (hardware.voltage() * 1000) / divider;
  voltage = 3300 / ratio;
  
  // get temperature in degrees Celsius
  temperatureC = (voltage - 500) / 10.0;
  
  server.log(postInit);
  
  // convert to degrees Farenheit
  temperatureF = (temperatureC * 9.0 / 5.0) + 32.0;
  
  server.log("temp: " + temperatureF);
  
  // set our output to desired temperature unit
  temp = temperatureF;
  
  
  if (postInit) {
    // check that temp is not more than +-15 degrees F diff from oldTemp
    if ( temp < (oldTemp - 15) || temp > (oldTemp + 15) ) {
        return;        
    } else {
        output.set(temp);
    }
  } else {
    // set the old temp val for reference the first time
    oldTemp = temp;
  }
  
  
  // over 70 is hot enought to trigger the alert light
  if (temp > 70) {
      hardware.pin2.write(1);
  } else {
      hardware.pin2.write(0);
  }
    
  // after function's first run set flag to true    
  postInit = true;
  
}

server.show(temp);

// Register with the server
imp.configure("Office Temp Sensor", [], [output]);

update_temp();