temperature displays

the real issue is the set-point. how would I make the temp display activate something at a specified temp? thats the tricky one since it has no options for that kind of thing... it just displays temp. so there is no way to signal when something should be turned on or off.

It depends on how it works.  If the temp probe is a simple voltlage coming back that represents temperature all you would need is an op amp wired in to the temp probe to make your own set point.  There is a thread on this site about adding a low gas indicator light, it has the circuit diagram that should work with this.Kevin Pierson

OHHHHH I see what your saying, the probe would send back a variable voltage based on temp. Find what the voltage is at the temp I want to activate the heater, and add an op amp to trigger a relay etc. I get the gist of it now, I just need to figure out if the probe sends out voltage, and how to do it all :) How would other probes work? The guy selling these is asian, and I don't think he reads english very well, So I want to be clear about what I'm asking him (IE if the probe sends back a voltage)

yes these units use a thermistor for the sensor. I ordered one. $12 CAD free shipping.....pretty good deal, except its 5v, so I will need to tap into a 5v power source, or use a resistor or something.

really how come? this what I need?? http://www.radioshack .com/product/index .jsp?productid=2062599 What kind of op amp would I need to trigger a relay at around 5 degrees celsius? or do I need to take a voltage reading to determine that?

On another note, if i wanted to add more sensors, would it be as easy as connecting them to a board, having them share the single input, and simply switching between which sensor is actively connected to the display? (if that made sense)

Yeah, that should work.Kevin Pierson

were you saying "that would work" for both questions?