PWM and BEMF

[Meriachee]

Hi,

Has anybody whipped up a circuit and some code to measure what's happening to a motor between outputs of PWM? I know that you can "measure" what the motor is doing between these outputs, but what I don't get is how.
It seems to me that a "stall" type of motor, like a "Tortoise" model RR motor would have a particular current draw when operating, and that draw would go up when the end of travel is reached. Assuming an H bridge, where would you measure the current? Or would you even measure current?

Anybody?

Cheers
Gary

[HenrikOlsson]

Hi,
Sensing BEMF allows you determine the speed of the motor. Sensing the current allows you to determine the amount of torque the motor is producing. You could detect a stalled motor by sensing the current. The easiest and most common way to sense current is to place a resistor between the bottom of the bridge and GND, called low side sensing. You now have a voltage across this resistor that is relative to the current thru the motor. (This is not always true depending on how you drive the bridge etc but it's the easiest way)

Have you seen the Microchip application notes on motor control:
DC Motor control tips & tricks (http://ww1.microchip.com/downloads/en/DeviceDoc/41233B.pdf)
Brushed DC Motor fundamentals (http://ww1.microchip.com/downloads/en/AppNotes/00905a.pdf)

/Henrik.

[Meriachee]

Thanks! I have seen these now...

Cheers
Gary