thank you for the reply, but I'm looking to remove the 9V and run off just the 4xAAs.

I'm new to electronics and arduino, so the answer I'm looking for will explain how to wire this to remove the 9V and use just the 4AAs.

How long are you hoping to have the thing running from a set of batteries ?
Is space / weight an issue ?

The 9V battery is a poor choise for powering the Arduino. It will not last long.

Depending on how often the heater is on it too will drain the 4 AA batteries pretty fast i think.

space/weight is def an issue.
it will be on intermittently for 60-90 minutes.  The "intermittently" depends on the temperature....it will be "on" when at or below a setpoint and "off" when at or above another setpoint.  The whole contraption is in a very thermodynamic insulated foam enclosure with reflective mylar interior...so it will be insulated as well as anything on earth, and have a very small space of just a few cubic inches to heat.

The temp outside however will be as low as -40C.

I think the 4 AAs will have sufficient capacity, but if testing turns out that it is not, then I'll up to a 6 pack.

any advice on how to get rid of the 9V and run the arduino on just the AAs?

I am a total arduino/electronics n00b.

The image below (.fzz attached) is for a circuit that will sense the temperature with the TMP36 sensor, and then turn a 5V heating element on or off depending on that temp reading.  I'm using the MOSFET instead of wiring directly to a 5V pin on the arduino simply because I'm afraid the .6 AMPS the heating element draws will fry the arduino chip.  The entire system needs to be portable (battery powered)

Two questions.

1.  I've only had one other forum look at this circuit.  So, please review it and let me know if I should change it or improve it in any way.
2.  I'd like to eliminate the 9V battery and run the arduino AND the heater off the bank of nimh AAs.  How would I modify the circuit to accomplish this?

thanks.

I think they are called "spring return rotary switches", but I still can't find anything useful.

what I am looking for is a a type of rotary switch, similar in functionality to those used in some higher end car stereo tuning knobs and/or volume controls.

the knob is lightly spring loaded, returning to a middle neutral position when you release the knob.  It has two positions: left and right.  rotate it to the right, and one of the legs of the switch goes hot until you release and it returns to neutral.  rotate it left, same thing but another different leg goes hot.

It would also (hopefully) have a third leg whose state is controlled by pushing the knob in.

I don't even know the proper name for this knob, so all my searches are coming up with nothing.

(I am not looking for a rotary encoder btw...actually looking to replace the rotary encoder currently in my circuit design with the much simpler multi-position switch)

you use that for fencing?

@ crossroads

regarding the image below from Nick Gammon's wire wrapped atmega board, I have three questions:

1.  Specifically regarding the resistors, caps, and LEDs...what is holding them in the socket?  Do the holes in those taper or something so they "grab" the wire, or is it just a tight fit like jamming a jumper in a femaler header?

2.  could you also just put the legs of those items through the board and wrap directly onto those instead of using the socket pins?  Curious why he chose to use those sockets for the components that have legs that are plenty long to get through the board and be wrapped.  (which is why I'm asking)

3.  what is the difference between those round socket pins and a female header?

Check out page 7 of the datasheet
http://www.sparkfun.com/datasheets/IC/MAX6675.pdf
Get some op-amps from www.dipmicro.com and duplicate the input buffer functionality, feeding the arduino analog pin.

man, you have to be the highest ratio of knowledge:helpful on this board.

I might need some help selecting the op amps, the first one (A1) is a special low noise amp (probably one of the maxim-ic products)

It would be great if they would tell us which of thier opamps they use on the 6675 chip...then I could just buy those!

here is a good video of wire wrapping


and a make online tutorial
http://blog.makezine.com/archive/2009/07/lost-knowledge-wire-wrapping.html

this is DEFINATELY what I'm looking for.

You really need a thermocouple amplifier.

yeah...well if it comes to that I'll use the MAX6675, but the freaking thing is $12 bucks and its only available in SMT.  I'mn pretty bad at regular through hole soldering...let alone SMT.  (the 6675 on a breakout board is over $20)

I was really just trying to crudely replicate the functionality of the max chip using code instead of the chip.  I can use a thermistor for the cold junction compensation reading.

I know it won't be as accurate as with the chip...I'm just wanting to figure out how accurate I can get using code and a thermistor ($1) instead of the max chip ($12)

I could do average of readings over time to mitigate the noise readings...

Got a spec on the thermocouple?

yes, sir..

http://www.sparkfun.com/products/251

gotcha, that makes more sense.  Thanks.

thank you crossroads, I think wire wrapping is exactly what I'm looking for.

Try using the internal 1.1V reference instead of the 5V Aref.
Then 1 bit will equal 1.1/1023 = 1.08mV instead of 5/1023 = 4.88mV.

Well...tried that, but it didn't work. Here is my code.

Have the thermocouple anode going to analog pin 0 and the cathode going to ground.

Code:

void setup() {
  Serial.begin(9600);
  analogReference(INTERNAL);
}

void loop() {
  float thermocoupleValue = analogRead(A0);
  Serial.println(thermocoupleValue, 5);
  delay(1000);
}

reads noise at first, till i hook up the TC, then drops to 0
805.00000
947.00000
578.00000
780.00000
523.00000
467.00000
816.00000
475.00000
632.00000
0.00000  <<here is where I connect thermocouple
0.00000
0.00000
0.00000
0.00000
0.00000

why does the book (written by one of the Ardunio guys Massimo Banzi) say arduino is Processing based, if its based in C?