Intellitouch guitar tuner

Staff -- 8/1/2002

If you play the guitar or any other string instruments, the Intellitouch guitar tuner will appeal to you on both a musical and a technical level. The tuner combines sensor technology with a microprocessor to produce musical measurements. It clamps onto an instrument and uses a piezoelectric sensor to sense vibration, not sound, so you can tune an instrument in a noisy area. The sensor generates an electrical signal in response to the vibration and sends the signal to a buffer amplifier. Figure 1 shows the block diagram of the tuner.

The amplifier's output connects directly to a microprocessor that cleans the signal and extracts the vibration's fundamental frequency. The microprocessor performs frequency analysis to find the closest note. Using its clock for a timebase, the microprocessor measures the wavelength of the vibration by calculating beats per second. It then converts the wavelength to frequency and applies the frequency to a lookup table and displays the nearest note.

As Figure 2 shows, the tuner's display contains three pairs of arrows. When all six arrows appear, the string is in tune. As the string's fundamental frequency moves away from the note's center frequency, the outermost arrows disappear first. For example, if the note is slightly sharp, the leftmost arrow will disappear first. If the string gets sharper, the next arrow will disappear, and so on.

The tuning arrows carry different weights relative to a note's center frequency. The music scale divides the frequency span between each half step into 100 frequency bins called "cents." A cent is 1% of the frequency span from a note to the next higher or lower note. (The frequency span between two adjacent notes is the frequency of the lower note times the twelfth root of two.) For example, the scale uses 100 cents between F and F sharp or between B and C. One octave encompasses 1200 cents.

On the tuner's display, the outermost arrows carry a weight of 1 cent. The innermost arrows carry a weight of 23 cents, which produces the finest resolution as a string approaches a note's center frequency. So, if your B string is flat by more than 1 cent (1% of the frequency span between B and B flat), the rightmost arrow will disappear from the display.

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