Electronic guitar tuner

Claim 1

An electronic device for tuning a stringed instrument comprising: transducing means for converting into an electrical signal the acoustic vibrations of a struck, plucked or bowed string; filter means for removing unwanted noise and overtones from said signal; amplifier and limiting means for rendering all excursions of said signal of equal amplitude for a sufficient time after the striking of the string to permit frequency measurement thereof; one-shot multivibrator means responsive to said signal for delivering pulses having frequency of said signal and having predetermined width determined by the internal parameters of said multivibrator means, so that the average DC value of said pulses becomes proportional to the frequency of said signal; filter means to extract the average DC value of said pulses; a DC reference voltage; means for compariNg said DC reference voltage and said average DC value, thereby to indicate whether the fundamental frequency of the struck string is above or below a predetermined frequency; a single DC supply voltage; transistor switching means following said multivibrator means for making said average DC value of pulses proportional to said DC supply voltage; voltage divider means for making said DC reference voltage also proportional to said DC supply voltage, so that both average DC value of pulses and reference voltage rise and fall together with changes in supply voltage, with the result that when the two voltages are matched by tuning to the correct frequency, their difference continues to be zero over a considerable range of supply voltage, making regulation unnecessary.