BioBoard/Documentation/Temperature

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Introduction to temperature

Building a thermometer

Digital thermometer

What you need

How to build it

Things to keep in mind

Thermistor

A thermistor is a type of resistor which has a very well known dependence of the resistance on temperature, and the change is quite steep so that we can resolve small differences in temperature. We are using them in place of thermometers, and they are sometimes referred to a "resistance thermometers" - they are inexpensive, easy to find, and are very easy to interface to the Arduino. They are specified mainly by their room temperature (25 C) resistance and a common value is 10 kOhms. If many models are available, like from a major electronics supply house, you can also specify the tolerance and you can choose from different shapes and sizes (the size of a match head is good for starters). As well, there are two general types of thermistors - ones that increase in resistance with increasing temperature (PTC) and those that decrease in temperature with increasing temperature (NTC).

What you need

Besides your Arduino, all you need is a standard resistor with a value that is the same as the room temperature resistance of your thermistor. You'll be building a "voltage divider" so that you can use the 5 VDC output of the Arduino and have good resolution over the full temperature range of the thermistor (usually something like -40 C to +125 C, perfect for biological experiments). For our examples we'll be using a 10 kOhm NTC thermistor (Sparkfun and Hacktronics carry these) with a 10 kOhm resistor for the bridge.

How to build it

Things to keep in mind

Interfacing and measuring

Calibrating a home-built thermometer

Making it cooler

Geeking out

Links