Electronics > Beginners
Dremel main board: puzzled about AC dark magic
Erwin Ried:
I have a broken Dremel 398 (with a small digital display that is always ON) and I am quite puzzled about 3 things (I am thinking maybe I could recreate the PCB with an Attiny, if I could understand about AC magic).
1) How they convert 230V AC to 5VCC for the PIC with so little components?
2) How do they detect the RPMs in the microcontroller only with 1 wire around the stator?
3) The microcontroller and LCD are always powered on, but there is a switch that turn the Dremel ON and OFF (with a soft start), how does the uC knows WHEN to do the soft start/stop?
PCB:
Thanks a lot for your time :)
Zero999:
I think you properly need to reverse engineer the PCB, to answer all your questions.
1) The microcontroller is probably powered using a capacitive dropper.
https://www.google.com/search?client=firefox-b-d&q=capacitive+dropper.
2) It might not use sensing at all and could be completely open loop.
3) I don't knwo, there isn't enough information about how the switch is wired up.
Erwin Ried:
--- Quote from: Zero999 on December 14, 2019, 11:56:21 pm ---I think you properly need to reverse engineer the PCB, to answer all your questions.
1) The microcontroller is probably powered using a capacitive dropper.
https://www.google.com/search?client=firefox-b-d&q=capacitive+dropper.
--- End quote ---
Great! probably yes, Ill try to reverse engineer the PCB. I removed most of the parts to test them but they are all fine (caps, triac, inductors, resistors). So the PIC or the small NPN transistor is one of the damaged parts.
--- Quote from: Zero999 on December 14, 2019, 11:56:21 pm ---2) It might not use sensing at all and could be completely open loop.
--- End quote ---
It has:
--- Code: ---Electronic feedback controller. Enchances overall torque and performance at low and mid-speed ranges.
--- End code ---
But as you see in the pcb, there is only 2 wires going to the brushes and 1 going to the stator armature :-//
Zero999:
--- Quote from: Erwin Ried on December 15, 2019, 12:01:56 am ---It has:
--- Code: ---Electronic feedback controller. Enchances overall torque and performance at low and mid-speed ranges.
--- End code ---
But as you see in the pcb, there is only 2 wires going to the brushes and 1 going to the stator armature :-//
--- End quote ---
There are ways to get the speed of a motor without two wire feedback such as: detecting the back EMF, or that wire could be picking up the electrical noise generated by the commutator, but it's possible there is no feedback at all and what you've read is just marketing BS.
schmitt trigger:
Dremel motors are (or at least the one I got) universal motors.
Meaning: series wound.
Perhaps this single wire is a stator (field) tap, where the motor current can be indirectly read?
As 0-999 mentioned, a full reverse engineering may be required.
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