![]() This stage is followed by a Schmitt trigger to give a clean square wave at the input frequency a square wave that will remain virtually constant until the guitar string has ceased to vibrate. The next stage produces a gain of 20, such high gain being required to produce a strong signal even though the decay of the string is fairly rapid. This high gain is tolerable because the effects of clipping of the signal are relatively unimportant in this circuit. The chosen values of R1, R2 set the gain of the first stage at 200. The low pass combination of C2, R2 attentuates frequencies above 338Hz, reducing the effect of harmonics and spurious noise etc. As we only need to deal with frequencies between 82.4 and 329.6Hz, the input is filtered by the high-pass combination of C5, R11, which attenuates frequencies below 72Hz and thus helps eliminate any mains hum pick-up. (Click image for higher resolution version) The frequency-to-voltage conversion is achieved by the single LM2917 chip (IC2).įigure 2. ![]() By the use of a frequency to voltage converting stage these are changed to DC voltage levels, which can be compared with reference voltages produced from a chain of high stability, close tolerance resistors, which are fed from a stabilised voltage supply. These are shown, for the six strings of the guitar, in Table 1. The accuracy of the device is quite sufficient to tune your guitar as well as can be done by ear alone, and remains at the set pitch with the battery voltage down as far as 8 volts (the unit being powered by only one PP3).īefore looking at the circuit operation it is best to consider the requirements of the unit i.e. To tune the selected string simply adjust both LED's to the same brightness and you're in tune. The system is extremely simple, using just two LED's, one for 'sharp' and one for 'flat'. For this reason the Guitar Tuner described here was designed, the objectives being to produce a guitar tuner as quick and simple as possible to use, with a price closer to the old faithful 'pitch pipes' than to its commercially produced, electronic counterpart. ![]() ![]() Unfortunately, they also carry a rather high price tag. There are of course electronic guitar tuners available and many are extremely good. I know from teaching basic guitar at evening classes that, with ten or twelve people trying to 'tune up' at the same time, the task is made almost impossible. Even when using traditional 'pitch pipes' this can still be a problem if the string is out of tune by more than a semitone or two. Many guitarists, especially beginners, experience difficulty in tuning their instruments. ![]()
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