crystal tuning fork

7-88 — elektor july/august 1981 91 crystal tuning fork The musician, who does not possess "perfect pitch", will no doubt occasionly have to use a tuning aid onic 440 Hz sound such as a tuning fork or an electr oscill arenot Hz generator. Low frequency 440oscillators edeally suited for use as "electronic tuning forks" because of their inherent instability. For this reason, the crystal controlled oscillator described here may well offer the best solution. Crystals with a frequency of 27.025 MHz for use in model radio control transmitters, are reasonably inexpensive and readily available. Such a crystal oscillates at a basic frequency of 9.0083 MH1z2, which when first divided by 5 and then by 12 yields a tone with a frequency of 439.86 Hz. Ideally, a crystal with a frequency of 27.035 MHz, channel 7 of American CB transceivers, would give slightly more accurate results (440.02 Hz), but these are, as yet, not readily available in the UK!. The division by 212 (---- 4096) can be obtai...