Buy an arduino mega, upload a reprap firmware, and in that firmware pins.h file, check or alter locations for step/dir/en pins, and from that arduino header take these to each motor.
For a thermistor its a votage divider with a resistor fixed for pullup to 5v, and thermistor on the gnd side, and the voltage divider output has a 10uF cap on it before it goes into the adc pin. This you can do in air or on a stripboard pcb (or whats the name of that).
For a heater its a low side mosfet, a header pin goes into gate, and mosfet can then be wired directly and mounted on a hefty heatsink, with only wires soldered to its legs.
Thats all the basics requirements, if you want a lcd and sd, those are extras and you can figure them out and wire them separately.
Or, if you want some other electronis, you could use any electronics out there, and draw the step/en/dir signals from the pololu headers, but probably wont be cheaper, nor a cleaner setup, and also you will end up with some of extra unnecessary stuff.
To note, you cannot use a controller "to just control the extruder head", because extruder head is integrated with all other movements, meaning extruder head is a fourth dimension, so x+y+z+extruder(s) all need to come from same controller.
For a thermistor its a votage divider with a resistor fixed for pullup to 5v, and thermistor on the gnd side, and the voltage divider output has a 10uF cap on it before it goes into the adc pin. This you can do in air or on a stripboard pcb (or whats the name of that).
For a heater its a low side mosfet, a header pin goes into gate, and mosfet can then be wired directly and mounted on a hefty heatsink, with only wires soldered to its legs.
Thats all the basics requirements, if you want a lcd and sd, those are extras and you can figure them out and wire them separately.
Or, if you want some other electronis, you could use any electronics out there, and draw the step/en/dir signals from the pololu headers, but probably wont be cheaper, nor a cleaner setup, and also you will end up with some of extra unnecessary stuff.
To note, you cannot use a controller "to just control the extruder head", because extruder head is integrated with all other movements, meaning extruder head is a fourth dimension, so x+y+z+extruder(s) all need to come from same controller.