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PT-100 connection to J-head extruder

Posted by htekin 
PT-100 connection to J-head extruder
June 10, 2014 02:53PM
Hi everybody,

I have built printer and connected everything but while connecting extruder thermistor, I am having trouble. How will I connect the thermistor or PT-100 Thermo couple to my board with pullup resistor. In marlin, it says with 1K or 4.7K pullup.
Please help me I am stucked.

Thanks everybody
Re: PT-100 connection to J-head extruder
June 11, 2014 09:29AM
Lots of boards already have 4.7K pullup resistors installed. You are basically making a voltage divider with the pullup connecting to the ADC reference voltage, and the ADC sensor pin connects to the junction between the pullup and the thermistor or PT-100, while the other end of the sensor connects to ground.

On most boards, the circuit is like part of the the schematic on [reprap.org] but without the R1.

PT-100s increase in resistance from 100 ohms by about 0.4 ohms/C, while a 100K thermistor decreases from 100K ohms at 25C with a more complicated behavior.
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