Watson Electronics
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This page is intended as an initial review of the current state of the art in reprap electronics. The ultimate goal is to look for areas where the quality of the electronics can be improved, the features expanded and the cost maintained or reduced.
Contents
Stepper Drivers
Temperature Measurement
Thermistor
Thermocouple
RTD
Silicon Based
Heater Control
Bang Bang
Bang Bang control is a method of on / off power control. The on and off time are controlled proportionally to maintain the average power delivered and needed to maintain a certain temperature. The reality is that this doesn't differ from PWM control except for the fact that bang bang control is typically implemented with on off cycles with a period of hundreds of milliseconds, or many seconds.
PWM
PWM control is an efficient method of proportional control which is much more power effecient than linear control. The disadvantages are that it can be audible at low frequencies (which is dwarfed by the audibility of the PWM stepper motors in most reprap designs) and at high frequencies switching losses can become significant. That said PWM control can easily be 90% efficient. One of the problems seen in several of the heater controller designs has been use of arbitrarily high frequencies. Frequencies above a few hundred Hz or a few KHz, although potentially audible, can not be exceeded without proper MOSFET drivers to pump the MOSFET gate capacitance. The higher the frequency, the more time the MOSFET spends in it's switching transition state which causes excess power loss. This is especially problematic when using microprocessor I/O pins to drive a MOSFET gate as they can not deliver enough current quickly enough to charge the gate and switch the MOSFET rapidly.
