Hi there.
I'm following this tutorial here:
http://www.arduino.cc/playground/ComponentLib/Thermistor2
Using the simple code.
But I'm getting a reading of '0' from the serial output,
and when i heat up the thermistor I get negative readings.
Pretty sure it's a PTC 10k thermistor.
If I remember correctly there is a simple fix for this, but I've forgotten
what it was.
when i heat up the thermistor I get negative readings.
Sounds like you have got the wiring wrong.
But I'm getting a reading of '0' from the serial output
The offset bias needs adjusting in the software. That's the bit where the analogue reading is converted into a temperature.
Where did you get the thermister? Did you purchase it "new" with a spec sheet available?
If you didn't, good luck figuring it out.
Some thermisters don't have a linear output vs temperature, which is where a spec sheet comes in (the manufacturer generally gives an equations and/or a graph of temperature vs. resistance).
If your thermister is linear, its fairly easy to figure out the graph; if not, you have some work ahead of you. If you don't have the spec sheet, and don't know what the part number or manufacturer is, assume it is linear first. Measure the temperature of an ice-water bath (assume 0 degrees celsius; you might want to use a calibrater thermometer here as well) with the thermister, note the temp. Plot the point. Then measure boiling water (100 degrees celcius - once again, use a calibrated thermometer as ref), plot the point.
Draw the line, find the mid-point. Note the resistance. Heat (or cool) something to that point, check to see if the resistance matches. If it does, its linear, if it doesn't, then it isn't, but at least you have another data point.
From there, you can keep an eye on it, and plot a point for each degree (using the calibrated thermometer as reference). It should be possible (though I don't know how off-hand) to convert that graph to an equation (probably involves a bit of calculus that I've long forgotten).
Good luck.
DOH!
I had the silly thing wired wrong.
Everything is groovy now.
Thanks for your replies
Everything is groovy now.
Wow - far out, man!
