The friend’s radio didn’t come with a frequency display ... explaining the problem, then measuring the radio outputs and testing to see that the Arduino can read them accurately.

We were struck by how attractive [mircemk’s] Arduino-based frequency counter ... There are at least three methods commonly used to measure frequency. Each has its pros and cons.

This is a well-known circuit dating at least back to the 1975 Fairchild ... the squared-up signal is sent to the 32-bit counter. To measure the frequency of this signal, the Arduino Nano waits for an ...