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Old 02-20-2011, 02:26 AM   #4391 (permalink)
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Originally Posted by MPaulHolmes View Post
Also, I wrote some gcode, and made 3 etched boards with a couple holes in each one so it will bolt right onto a bus bar. I also soldered a little high magnetic field current sensor to one of them.
With this change in hardware, have you considered changing the current sensor reporting polarity?

We started by using our current sensor in positive output orientation (2.5V->5V with increasing motor current), just as with Cougar.

We recently changed to negative output, 2.5V->0, so that we have the option to use a 3.3V or 3V A/D reference. This allows us to use faster microcontrollers that only run at 3.3V or lower.

Implementing this is easy -- just put the current sensor on backwards. We still use the same 5V supply, since most current sensors won't run on less than 5V.

We did need to make one other minor change. Our circuit has a high value resistor (100Kohm) on the A/D converter input so that we can detect when the current sensor isn't hooked up. (When disconnected, we fall back to proportional PWM mode.) We changed this to bias to ground instead of +V. Although either extreme raises a fault, biasing to higher current protects against a flaky connector.

Last edited by DJBecker; 02-21-2011 at 12:37 AM..
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