LM335
LM335 is a low-cost "precision" temperature sensor "operating as a 2-terminal Zener and the breakdown voltage is directly proportional to the absolute temperature at 10mV/°K" (from the datasheet).
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Pinouts
For the TO-92 package, looking at the flat side, with the legs down, the left pin is "adj", middle is "V+" and right pin is "V-".
Specs
The datasheet claims a current range of 400uA - 5mA.
Use with XBee
The XBee module has a 10-bit ADC with inputs from several pins. With VRef connected to VCC (3.3VDC for XBee), the sampling range is 0 - 3.3VDC or a resolution of approx. 3.3mV. The input voltage must not exceed VCC + 0.3V (3.6V).
For the LM335, this corresponds to a measurement of up to 360K, or 87degC, although the top measurement will be 330K, or 57degC and the resolution will be 1/3degC per lsb (3.3mv/lsb / 10mv/K). This seems adequate for most domestic and outdoor measuring, ie. range up to 57degC, maximum of 87degC.
We use the LM335 with a pull-up to the +5V supply. At room temp (approx 300K), we get a drop of 5V - 3.00V = 2V. Designing for a current of 1mA, that gives us a 2k pull-up resistor. With this pull-up, the current through the LM335 will stay above the 400uA minimum as the temperature rises to 420K (147degC) (5V - 4.20v = 0.8v, divide by 2k gives 400uA). At 0K (!), the current will still be 5V/2kR = 2.5mA, still within the required limits.
