Hi,

I am trying to interface a uP (Atmel AVR 328p) with a variable reluctor sensor. This is the type that generates an AC waveform as metal teeth move past the sensor. I think the voltage level increases with speed of rotation. I have been thinking of using a comparator to detect 0 crossing. I guess the comparator won't mind about the voltage as long as it doesn't exceed the device's limits for its input voltage.The one thing I am not sure about is the effects of noise as the signal crosses 0, this may cause multiple outputs as the signal crosses 0. I can think of two ways to deal with this.

1. RC filter
2. Hysteresis

I'm not sure wether an RC filter would be good enough to completely eliminate this issue and I'm not sure if hysteresis will work as the output voltatge of the comparator (LM399) using a regulated 5V isn't constant with respect to the voltage generated by the reluctor sensor. So any feedback voltage is undetermined.

Any ideas?

 

Program the uC to accept a valid input if the voltage on the input is stable for an amount of time.

 

Thanks for the suggestion, I would rather do it in hardware though as I will use the input as an interrupt trigger. This is up to 15khz frequency.

 

This circuit is used in the design I am working on, however I don't know what the chip FI2438-03 is. Does anyone have an Idea of how this circuit might work?