Using electronic diagram below can be built electronic tuning fork. A standard tuning fork produces a sound of 440 Hz.
An oscillator, a divider, a speaker and power supply modules are all needed. Oscillator is built with gates N1, N2 and adjusted with variable capacitor C2 to 1,000,120 Hz (if possible, with a Frequencymeter). Oscillator output is applied to IC2, which divide by 2273.
In this case, the Q11 output of IC2 is now almost symmetrical signal of 440 Hz.
Signal is then separated from the gates of N3 ... N6 and balanced output stage gives a level low enough for a speaker.