Dc motor speed control

SAborn

Senior Member
Im still not sure how that will work with the OP motor as he needs to turn the coil off and on during each rev, while monitoring the hall sensor at the same time.

Post 237 you commented on switching each coil seperate (bit like a stepper motor), this would make the timing even harder to control the coil duty cycle with the circuit used.

Dont get me wrong as i had thought of these methods too, but kept finding problems with how the picaxe could manage all functions with correct timing without effecting each other function.
Then concluded that the willingness to make changes to the circuit or changes to components used was not a option the OP wanted to do, so its like flogging a dead horse, it aint going anywhere.
 

boriz

Senior Member
Forget separate coil switching. It's easier just to go with the existing circuit (one MOSFET) and switch all the coils at once.

Did you read the pseudo code?

Power to the coils is removed for one complete rev. Or two complete revs, or three etc...

It's a bit like PWM with the frequency being set by the speed of rotation. IE: 1 rev off, 9 revs on, repeat = 90% duty, regardless of absolute speed.

The pseudo code is far from a complete program, but it should illustrate one way of doing it.
 

Goeytex

Senior Member
Attached is a drawing of a circuit that gates a Picaxe Generated PWM with the signal from a Hall Switch. A second Hall Switch provides an additional input that can be used for speed sensing.

The 74HC132 replaces the P-FETs in the original proposed circuit. It is simply used as an inverter and as an AND gate to "AND" the Hall switch signal and the PWM. The gated pwm signal is then sent to a Microchip MCP1407 Driver which in turn drives the MOSFET.

This circuit will work very well as drawn. That is, it will generate a clean gated PWM and will drive any Power MOSFET adequately. However, whether or not a motor such as the OP has vaguely described can be controlled as he has proposed ....is yet to be proven.

I am not confident that the proposed method of control is appropriate or technically sound.
 

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