I updated this one a bit. The bottom sinusoid is the reference frequency, and the top left signal is the signal frequency that is to be measured. The reference should always be smaller than the input signal.
If the reference frequency is 10Hz and the SSD displays a 9, you multiply 9 by 10 Hz to find the frequency of the input signal, which is 90 Hz as in the circuit.
The reference signal and incoming signal can be altered to test the system.
Please tell me if something is not working.
