tuning fork - with electronic prongs

tuning fork... elektor october 1984 By definition, a tuning fork is a two-pronged metal object set in vibration to produce a sound which serves to check the pitch of instruments and to give the pitch to voices. Its tone is virtually a pure note, lacking the upper harmonics which enter into the tone of normal instruments. The design presented here is a change from the basic device in two important aspects: the two prongs have become electronic circuits, and instead of a single tone it provides a frequency range of 32...7902 Hz in semi-tone steps. tuning fork . . . ...with electronic prongs One of the two prongs is a stable reference oscillator, which is controlled by a 4 MHz crystal, and the other consists of an a.f. amplifier driven by an Electret condenser microphone. The output of the prongs is applied to a frequency com- parator. Some background information All musical instruments produce sounds which do not consist only of pure tones (like that of a tuning fork) but of a mixtu...