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Unread 09-02-2003, 01:03
jskene jskene is offline
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We are planning to put a simple comparator circuit across the ground lead of each motor. By comparing the voltage drop across this wire to a reference produced by a trim pot, the computer can determine when the motor is stalled, or at least drawing sufficient current to trip the breaker. The program will then automatically reduce power to the motors.
This will be especially useful during the autonomous period, when we might try to drive through a wall at full speed.

We also plan to use this circuit to detect that the window motor has reached the end of its turning point, rather than use limit switches. Limit switches have a habit of breaking at inopportune times.

By using the ground lead instead of the +12V lead you can use a garden variety comparator that senses down to ground, like the LM339. The open-collector output can be connected directly to a digital input on the robot controller, with no need for zener diode over-voltage protection. You would want to put a low-pass filter (series resistor with a capacitor to ground) on the input to remove the pulse-width-modulation pulses, as it is the average current you are interested in measuring.

I could post a schematic if anyone is interested.

Last edited by jskene : 09-02-2003 at 01:20.
 


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