Macgyvering a thermistor for Rapman

Hi, I am very close to finishing a Rapman I recently purchased. However, due to my failure at electronics, I have since ripped the legs off of two innocent 200k thermistors. I am now just as broke as the thermistors, in terms of cash. I don't have the coin to order any more from England. However, I have come up with some ways to hack the data the thermistor would provide, until I get paid in a month. I could...
1. Use a resistor to mimic the resistance that the thermistor would provide at room temperature. The problem I see with this is that the extruder would continue to heat up until it reached the desired temperature, which would be never, as indicated by the resistor. Something would give out.
2. Use a resistor to mimic the resistance that the thermistor would provide at plastic melting temperature. The problem I see with this is that the extruder would see itself already at full temperature, and warm up quite slowly, or not at all.
3. Use a potentiometer to dial in specific resistances. The problem I see with this is that it would require calibration which may affect the extruder.
4. Run it without any thermistor, just a wire between the two ports.

Which of these is the best option in terms of safety and practicality? Anyone willing to donate a 200k thermistor to a worthy cause?

can't you control the heater itself manually?

or

I'm thinking that you could use a SPDT switch, have the room temperature value resistor on one side, and the heated one on the other, and the common terminal to one side of the thermistor connectors on the board. BOTH resistor's leads will connect to the other terminal.

ask someone else if you need clarification.

or maybe me:

extruder------------------|------resistor 2
controller---------   resistor 1   |
                  |       |        |
                  |____ SPDT--------

You need a voltage proportional to a temperature of something.picture in next floor.the NO.4 picture is The table of the relationship between temperature and voltage.
another way is Alcohol thermometer diy.

With the transistor's PN junction to measure the temperature
This is an old way,The last century use of 70 to 80 years,the PN junction V_f-T characteristics.More than 100 degrees Celsius may not work.picture in next floor.

I am going to use the first schemat. For those of you with a printer involving a 200k thermistor, how much resistance does it give at full temperature? For those with a 100k, how much does yours read?

i used thermocouple sensor ,I did not get thermistor.hintss answer is correct.

for 4,i have a not good idae, you can let the program set a timer to determine the relationship between time and temperature curve.

just to be clear, the common lead of the SPDT in my solution connected to the extruder controller.

Just thought of a good MacGyver solution: Pull the thermistor out of a remote-probe oven thermometer. You will have to determine resistance and Beta by experiment but it should be a reasonable replacement. Typically the pointed probe tube is crimped over the silicone-insulated cable. A sharp edged file should let you weaken the tube below the crimp and break it off.

or just break the cable

Well, I can't exactly reprogram the board, it being a Rapman and all.

ZaphodBeeblebrox,I think, you need learn the program.

Edited 5 time(s). Last edit at 05/25/2010 12:48PM by tuziluobo.

No, arduino programming is no sweat, but I don't want to screw with a preprogrammed board. I've had some bad experiences, invilving quite a lot of magical blue smoke.