Controlling HeatBed Temperature? How

Just wondering how people control the heatbed temperature when using a board that doesn't support Heatbed temp control? Any thoughts and insight would be much appreciated.

Cheers
Paul

I'd probably just whip something up on breadboard myself. Feed your voltage through the thermistor and a resistor and tap the voltage at the middle to get the temperature reading, call this A:

+5V ----- THERMISTOR ----- 4k7 RESISTOR ----- GND
                       |
                       A

Next hook your power across a potentiometer and tap the middle pin to get a reference voltage (temperature) that you can control, call this B:

+5V ----- 10K POT ----- GND
             |
             B

Then feed those both into a 741 op amp. Normally the output will be low, but when the thermistor temperature exceeds your reference temperature the op amp will swing high, so sue it to drive the power mosfet sinking your heatbed to ground:

                                   HEAT BED
        ___                          |
A -----|OP |                       |/
       |AMP| --- 1K RESISTOR ----- |  POWER MOSFET
B -----|___|                       |\
                                     |
                                    GND

(A goes to the negative input, B goes to the positive).

That's 4 components, costs about $5 and takes about 5 minutes to solder up. This is an on/off controller, although personally I've never had any problem with them. If you want a PID controller then your're going to have to incorporate an atmega into the circuit or use an off-the-shelf solution.

Thanks for the info. Looks like it should do the trick as I mainly use only a few temperatures. My second board is a Gen 6 and doesn't support heat bead control, so this could be a good solution. Thanks again