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Marty56
To my understanding, the RAMBO board has separate power inputs for the bed, mosfets, as well as the motors and logic. Would it be possible to supply different voltages to each of the power inputs?
Yes
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For example, could I supply 12 or 24V to the logic power input while supplying 5V to the mosfet input?
Minimum voltage is 12V. Maximum is 24 (v1.0-1.1) or 35 (v1.2) The 5V for the microcontroller is regulated down via a switching mode power supply from either the motor power (v1-1.1) or extruder/fan (v1.2). You don't have to supply the 5V.
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Also, the fan outputs on RAMBO are also mosfet controlled correct?
Yes
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I would be able to use a fan at variable speeds from each output instead of just being able to turn a fan off and on?
Yes, just set the duty cycle for that pin in your firmware to the speed you want.