Thermistor and Stepper motor

Hey I am new at Arduino and had afew questions about it. First, i have a Thermistor i tore out of an old electronic thermometer, i know no details about it but i can see that its resistance changes depending on temperature on a multimeter, i just cant get arduino analog in to recognize it. Also I have afew stepper motors i got out of an old dot matrix printer. I was looking at ladyada's motor driver that can handle 2 steppers but i was interested in running 3 or 4 off the same arduino, would this need another micro controller (like a pic+motor driver) with more analog outputs to send serial commands to from the arduino? Also What is the diffrence between a transistor and a relay? Thanks alot mool

A transistor is made of silicon, while relays are mechanical devices.

The motor shield can only do 2 steppers, as you've said. If you wanted to do 3 or 4, you probably can with the Arduino since the motor shield has a separate power source AFAIK, but you'd have to do it yourself. You can take a look at ladyada's schematic, and figure out how to get more i/o to accommodate your extra steppers.

And for your thermistor... to "calibrate" it so you can get the temperature in Arduino sketches, you need to get its resistance at at least two known temperatures, and then using those points, you can guesstimate in your code. More points may be helpful, in case the resistance doesn't increase in a linear fashion.

Anyway. Hope that helps. (:

A transistor is made of silicon, while relays are mechanical devices.

The motor shield can only do 2 steppers, as you've said. If you wanted to do 3 or 4, you probably can with the Arduino since the motor shield has a separate power source AFAIK, but you'd have to do it yourself. You can take a look at ladyada's schematic, and figure out how to get more i/o to accommodate your extra steppers.

And for your thermistor... to "calibrate" it so you can get the temperature in Arduino sketches, you need to get its resistance at at least two known temperatures, and then using those points, you can guesstimate in your code. More points may be helpful, in case the resistance doesn't increase in a linear fashion.

Anyway. Hope that helps. (:

thanks, my thermistor issue is not that i don't know what the analog inputs are, its that i cant get any info. I used the sample code that sends the resistance of a knob over serial and with the thermistor im not getting any legible numerical data from the thermistor at all! i think its a hardware thing.

and sorry for dp, but how would the motor board make multiple outputs of one? do the stepper motor drivers accept serial commands?

Most stepper motors will need 4 Arduino pins to be controlled. so you could run 3 from the Arduino board without multiplexing the digital outputs.

Unipolar steppers (usually 5 or 6 wires) are easier to control than bipolar (usually 4 wires). Bipolar steppers need an H bridge to be controlled because the current have to be switched (reversed) with each step.

To save pins on the Arduino board you could use an IC like the UCN5804 (expensieve) which does all the stepping logic for you and only need two pins one for step (clocking) input, and one for direction. This IC also allows you to do half stepping. But it only works with unipolar steppers.

No matter how you drive your stepper motors they should be powered from an external power supply to avoid drawing more current from the Arduino board than it can handle.

EDIT: These two sites contain lots of good info on steppermotors. It's primarily about controlling steppermotors from a PC parallelport, but thats essentially the same as doing it with Arduino, if you just think of a parallel port as 8 digital Arduino pins.

http://www.doc.ic.ac.uk/~ih/doc/stepper/control2/connect.html#5804

http://www.doc.ic.ac.uk/~ih/doc/stepper/

Thanks :) how would you multiplex them though?

You can do it with shiftregisters. There's an example i the playground here :

http://www.arduino.cc/en/Tutorial/ShiftOut

Did you get your thermistor working poperly?