electronic tuning fork

10 electronic tuning fork A standard tuning fork produces a tone of 440 Hz, that is, the inter- national A (orchestral pitch). It is not very difficult to make an elec- tronic alternative. An oscillator, a divider, a loudspeaker and a battery are all that is required. To be useful, an "electronic tuning fork" must, of course, be a compact unit. As the use of special, and therefore costly, crystals was precluded, a little research showed that it would be possible to use relatively simple and standard components. It ap- peared that the required frequency can be derived from a readily avail- able 1 MHz crystal which, by means of a trimmer, can be pulled to 1,000,120 Hz which is the nearest frequency containing a whole num- ber ti mes 440 Hz. The oscillator is constructed a- round gates Nl, N2 and tuned to 1,000,120 Hz (with a frequency counter if possible), by means of trimmer C2. The oscillator output is fed to 1C2 which divides bv 2273 (2° +2s +26 +27+211). A practically symmetric...