Michael O'BrienThanks Mouser!
Just about every 10 mOhm or under TO-252-3 MOSFET Mouser lists is not a TO-252, but a TO-263, D2PAK not DPAK. I didn't check the nomenclature in the datasheet of the PSMR90-30BL. My bad, but c'mon, please? Went to digikey and they carry Alpha & Omega transistors. The AOD484 in the Select Mini is cheap @ $0.55 in single quantity and it has a cousin, the AOD240, that's $1.35 in single quantity. At ~150 Hz, the switching characteristics won't matter much between the two.
There is a possible side effect using the AOD240 too. With the higher Vgs, given that these transistors switch the main power to the heater, it may be quite possible to run this board off of 24 V. I don't have the PN off hand of the 3.3 V SMPS on the board, but my memory is telling me that it was compatible with up to a 40 V input. Still need to dig over the driver board a bit more cause the hot end fan is switched with on 2 pins of the STM32 and then the SOT23 transistor, i.e. why don't we have PWM fan control?
EDIT: The AOD240 has too much of a lead time. A similarly spec AOD510 seems to be a sufficient enough upgrade. It's RDSon is better at 3.3 V, but admitedly I've not observed the Vgs voltage on my scope yet.
To note, my fan will be working again later today with replacement SOT-23 MOSFET. Squashing the noise in the thermistor lines is the key to the stability of the PID loop from what I can read up on and I'm close to characterizing 'C' & 'L' with some help of various PID tuning guides and watching may 'scope :). I have a local electronics shop that carries some RF chokes that I hope will help out from, given what I've observed so far.
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Thermocouples are much more sensitive to noise. I figure this is due to the software end of the microcontroller and if Malyan implemented just a simple a rolling average filter, say with a 0.5 second duration, I'd quite sure we could get away with better PID control.
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I've never understood why thermistors are wired the way they are in 3d printers. It's a terrible idea to connect a sensor that is very sensitive to noise via a long, unbalanced piece of wire! Filastruder sells thermocouple amp boards that convert the tc output voltage into something a Mega's ADC can read. I've been thinking of something similar for thermistors, but instead of outputting a voltage, just connect them as slaves on a SPI bus. The wiring would definitely be more complicated, but the temp readings would be much more stable and accurate. Of course, then you'd need to modify the firmware to read the temp from a comm bus instead of an ADC. Since the Mini is closed source, that's a roadblock.
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