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Topic: Cheap alternative to Thermocouples? (Read 1 time) previous topic - next topic

Hi I've found some nice thermistors that have a measuring range of -55°C to +300°C


I just wondered what I will need to use these? as there 5kOhm will I need an OpApm or a whole circuit to power these?

I realise that the arduino only has 1024 'levels' availible but that should be fine if I can measure between 0°C  - 250°C then I can get a resolution of around .25 or a degree is that right? It only really needs to be accurate to 1°C for my purposes.



What do you think? I'm an arduino newbie and don't have much electronics experience.

Grumpy_Mike

Quote
will I need an OpApm or a whole circuit to power these?

No.
All you need to do is to connect them between the analogue input and ground. Then put a resistor from the same input to the +5V line. The value of this resistor should be approximately the same as the resistance of your thermistor at the mid temprature you want to measure.

Ahh so simple, like forward biasing a transistor.

Thanks mike  :)


jackrae

Bear in mind they are non-linear devices so you'll need to include an equation into your programme to make sense of the input voltages.
Suggested reading here http://en.wikipedia.org/wiki/Thermistor

tkbyd

Unless you really need such a wide sensing range, the Dallas 1-Wire chips are MUCH better... at not a great deal more complexity to use.

DS18B20 range: -10C to +85C

Yes... they take a little "getting to grips with"... but once you're there, you have an easy, reliable, high prescision... at the end of long wires... sensor.

And "DS1820" must be code for "Viagra" for the number of auctions you'll find on eBay for the things!

Actually using a thermistor is a good solution, they are cheap, easy to connect and available in a wide range.
The following page shows you how to connect, you need to use a lookup table to calculate the actual temperature in the arduino.
http://arduino.cc/playground/ComponentLib/Thermistor
You have to use the right lookup table for your chosen thermistor, which can be calculated using the steinhart formula:
http://www.resistorguide.com/ntc-thermistor/

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