toolboard out2 tacho validity
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https://docs.duet3d.com/Duet3D_hardware/Duet_3_family/Duet_3_Toolboard_1LC has a statement "the tacho reading is valid only when running the fan at full speed" referring to OUT_2 (the three wire fan connection).
In what way is the signal invalid when not at full speed? In particular, can it be used to determine reliably whether or not the fan is turning? That is, even if the actual value might be badly wrong, can it be relied upon to indicate that the fan is actually spinning rather than stalled, or might it give an apparently realistic value even with a stopped rotor?
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@achrn its only valid at full speed because the 3 waire fan has no way of varying the speed other than by "turning it on and off again" i.e PWM to the GND line. As to if you could say, as long as its >0 then its at least turning. that may work,but depends on the fan in question and would need testing.
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@T3P3Tony OK, thanks. So I think you're saying it's more a case of when you're driving a fan that way who knows what it puts out on the tacho wire, rather than that the toolboard is for some reason not able to read that tacho wire accurately?
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@achrn yes, the output is undefined if you PWM a 3 wire fan.
