Hi All

I have a device outputting 5V at a frequency of 'x' cycles per second under unactivated conditions. When the device is activated, while the Voltage remains the same, the frequency goes upto 10 times 'x'.

I would like to use an AT89c51 to track the frequency changes, and trigger a relay every time the device is activated.

Any suggestions on how I can measure frequency changes using an AT89c51?

Regards
Pramod