ant cosier wrote:
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if you use a hall sensor how would the micro read it



There are a number of Hall sensors in the market that are able to produce a PWM output signal. One such type is the Micronas HAL810 as can be studied at the following data sheet link: http://www.micronas.com/products/...10_3ds.pdf

The PWM type eliminates the need for an A/D converter and is measured using a pulse width capture measurement with a microcontroller timer. PWM type Hall sensors also lend themselves nicely to a sensor that is located far from the microcontroller and/or in applications where the Hall detector signal must be passed through an opto-coupler.

Michael Karas