TMP36/TMP37 Temperature Sensor
The Analog Devices TMP36/7 is a temperature sensor with an analogue output proportional to temperature, housed in a three-lead transistor style TO-92 package.
They work with 2.7V to 5.5V, and draw 0.05mA. You just need to connect them to an analogue input.
Reading the TMP36
(defun tmp36-temp (a) (- (/ (* (analogread a) 125) 256) 50))
Reading the TMP37
The TMP37 gives a voltage of 20mV per °C, and 0mV at 0°C, so the temperature in degrees is given by:
(defun tmp37-temp (a)
(/ (* (analogread a) 125) 512))
In each case the parameter is the pin number of the analogue input you're using.