The frequency being measured is the AC voltage source in the bottom left corner. This is counted against the reference frequency adjacent to it.
Only 10 Hz resolution & 0 - 990 Hz.
Have to wait a while for the pulse to complete from the reference frequency :(
On this version, used two op amps to double the input frequency. These are set up to with a narrow pulse width to give separation between the pulses. Reference frequency also doubled. This gives a slightly faster time to measure the frequency.
