Arduino thermister is giving wrong values?

Using Arduino Sensors
1

So I have a 10k resistor I just got in the mail, and hooked it up according to the schematic from the playground thermistor tutorial here:
http://playground.arduino.cc/ComponentLib/Thermistor

I have +5 to the thermistor, analog input in the middle, and ground on the 10k resistor.

My temperature of my work surface is 25 Celsius, or on the spreadsheet they provide, somewhere near 508.

The problem is that my serial readout is giving a steady 235, or basically 0 Celsius.

What gives? I was super excited because I have all the parts to finish my project right away with some coding but the thermistor just isn't working.

I am using these 10k thermistors, but any 10k thermistor should work right? How could that be the problem?
http://www.ebay.ca/itm/140353824494?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

2

I have tried the one other example they link to in the bottom section and it is working fairly well, it's reading a bit above 23 Celsius, and 391 ADC, maybe I just need to use this one, see what I am doing is changing an RGB LEDs color based on temperature and it's going to be on an attiny85v, I'd rather use the other code but if I have to I can probably use this.

3

I was wondering if anyone knows how to modify the script so that this would run properly on 3 volts, I'm not sure where I would start. I changed the voltage that was in the script but I only get 8 C as the reading.

4

It could be a coding problem but who would know? Nobody has seen it.

Thermistors are non linear and never that accurate anyway, although these shortcoming are unlikely to be the sole cause of your strife. I hope it isn't too late to say this but I don't know why you would bother with a thermistor these days. A DS18B20 is dirt cheap, robust, accurate, dead easy to use, works in the range you want, runs on 3v without any extra consideration, and talks to you in plain English. In short, God's gift, with no dependance on the accuracy on the other resistor in the divder, and no lookup tables.

5

Well, I had not known about those until now, I'm going to order some right away, and hopefully it will be fairly simple to get the temperature reading from them.

6

Ah! So it wasn't too late. ....

I'm sure you wont regret the move. The best tutorial I found is here

which is a good, plain, no-nonsense approach. It is geared for multiple sensors but is sensible to use even if you only have one.

7

I don't know why you would bother with a thermistor these days.

With a thermistor I can do 1000++ samples per second with an accuracy of 1-2C,
while the DS18B20 can do max 20 samples per second (1C precision) or 1.3 samples /second (0.07 C precision)

The sensors have a different working range (high speed low res) versus (low speed high res).
So in the end it depends on the application which sensor to use...