Questions regarding thermistor connections

Forum 2005-2010 (read only) Hardware Interfacing
1

Hello,
I have a thermistor and checked out a great example of how to use it at:
http://www.arduino.cc/playground/ComponentLib/Thermistor


The diagram calls for a 10K resistor. I have 3x 330R resistors. Can I chain link them, and will 990R work for short usage? It's only 10R off correct?

I'm fairly new to these diagrams, and was thrown off by the analog pin connection. Does the following make sense?
-connect 5V power pin to thermistor (assuming it doesn't matter which way to plug in a thermistor, same as resistors)
-connect thermistor to 10K resistor
-connect pin 11 to same side of 10K resistor that the thermistor is plugged to
-plug 10K resistor to ground

Thanks for the assistance in advance! :smiley:

2

Your calculations are not correct.

3 330R resistors in series is less than 1K so you are off by more than factor 10 !!

3

Oh man. It's way too early in the morning. Off to the parts store this weekend!

What about the connections? Do those work?

4

The connections looks ok.

This is the standard way of hooking a "resistor type" sensor up to an analog in, as a voltage divider.

5

Awesome. Thanks! I should be set (and not frying things). :slight_smile:

6

The more usual way of drawing a thermistor is to have a normal resistor but with a line with arrow going diagonally through the resistor.

A bit like Thermistor - Wikipedia although I would put an arrow on the end and not the flat.

The way you have draw in it looks like there should be three connections and there is only two.
The other way is to draw it like you have but to draw a connection between the middle connection (wiper) and one end.

7

Where's the hockey stick?!

Yeah the diagram looks ok apart from that.

I'm fairly new to these diagrams, and was thrown off by the analog pin connection.

You can think of the analog pin as a 'ground' and the current is going from the 5v through the resistance of the thermistor and to ground.

The 'real' ground is there to keep the pin low, the analog read pin does not actually work as a ground so you need a ground to sink the current.
The resistor is needed to stop all of the current going to the ground pin.

There's probably a better way to describe it but I hope that makes sense.

Mowcius

8

Actually, I didn't draw the diagram myself. I was just trying to interpret from the initial source linked in my first post.

mowcius, your explanation makes sense.. I just keep thinking of water in a river rather than electrons (may not be healthy, but helps visualize).

Thanks for the help!

9

Well often when you learn about things like that with you get taught with water pipes and flow valves so that is not a bad way to think about it. :smiley:

Mowcius