Piano tuner - Patent Review 6479738

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BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates to tuning devices, and more particularly to a device that attaches to the strings of a piano and has magnetic pickups over the strings for tuning the piano.

2. Background of the Invention

Musical instruments have been tuned in a variety of ways using both mechanical and electronic devices. One conventional method for tuning a piano requires an experienced tuner to manually turn the tuning pins with a special wrench. The tuner then determines when it is in tune by either using a tuning fork or an electronic strobe tuner as aids and systematically tuning each string using complex, learned methods.

Another prior art method of tuning musical instruments employs measurements made of the inharmonicities of three notes. One of the three notes is a standard note tuned to standard frequency.

Another prior art method determines tuning frequencies for an instrument by sounding at least three notes on the instrument which are recorded and digitally filtered to generate directly partial ladders representative of the notes.

However, the prior art does not disclose an apparatus or method for comparing a value for a tuning period against a baseline period value in order to evaluate a tuning signal.

SUMMARY OF THE INVENTION

This invention relates to a device for tuning a musical instrument that preferably attaches to adjacent strings of the instrument and positions magnetic pickups over the strings with the magnetic pickups detecting the vibration of the strings. Preferably, the device includes a detector operable to receive string vibrations and to produce a detected signal. In a preferred embodiment, the device also includes a processor operable to receive the detected signal and determine a first value for a tuning period of the detected signal, and to compare the first value for the tuning period of the detected signal to a second value for a baseline period of a musical note to evaluate the detected signal.

It is an object of the present invention to provide for an improved tuning device.

Another object is to provide for such a device wherein there are three strings of the piano with magnetic pickups over the strings, which pickups are used to detect vibrations of the strings without interfering with the strings.

These and other objects and advantages of the present invention will become apparent to readers from a consideration of the ensuing description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a schematic top view of the present invention showing a housing with extending lines to the piano strings.

FIG. 1(b) is a schematic side view of the FIG. 1(a) positioned with the same extending lines before being attached to the strings of a piano.

FIG. 1(c) is a schematic side view of the present invention showing the engagement of the underside of the housing with three different sets of piano strings.

FIG. 2 is a diagram of the detected signals as observed on an oscilloscope.

FIG. 3 is a block diagram of the programmable timer chip used.

FIG. 4 is a block diagram of the circuit used in the present invention.

DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1(a) is a schematic top view of the present invention showing a housing 1 with extending lines 3 that indicate how the housing would normally be positioned on the lower piano strings 5 of the piano to be tuned. A push on and push off power button 4 is located on the top of the housing for power control of internal electronic circuits. The extension lines 3 to the piano strings are the same in all the FIG. 1 (a) to FIG. 1 (c) views. The housing 1 is made of a material like plastic, which is not affected by magnetic fields. The purpose of the internal electronics is to both make calculations based on the detected readings and provide for the transmission of data from the readings. The detected readings made by the magnetic attachments are made to piano strings, and the readings represent vibrations of each string. Based on the readings, the internal electronics determine what note is being tuned and the degree that the note is out-of-tune. This determined value is transmitted via infrared LEDs (light emitting diodes) 7 (see FIGS. 1(a) and 1(b)) similar to a television remote control, to a mechanical unit, not shown, where the transmitted signal is evaluated and appropriate mechanical action is automatically initiated to bring the note into perfect tune. Other transmission modes can be used, such as radio communications.

There are infrared transmitters 7 on both opposite sides of the housing 1 so that the housing may be placed either way on the strings. The information from the housing is transmitted in opposite order for each side to keep it compatible with the placement of wrench heads upon tuning pins of the piano. The pickup device in housing 1 may be used independent of the mechanical unit used for the automatic manual tuning and has an integral LCD readout 8 on its exposed upper face, see FIG. 1(a), which displays the note being tuned alphanumerically as well as the amount that each of the three strings is out-of-tune with individual bar graphs 10. The readout 8 can be considered a viewable digital display which indicates the note being detected and bar graphs 10 indicate how many cents sharp or flat, or error, for the same note under observation.

In FIG. 1(a), four spaced magnetic pickups 9, or detectors, are shown, in dotted line format, on the underside or bottom of the housing 1. Small protrusions, or ridges, 11 (see FIG. 1(b)) are molded into the plastic housing 1 and act as spacers between the piano strings. These protrusions or ridges 11 engage with strings adjacent to the ones being tuned and ensure that the pickup coils are properly aligned with their respective strings. The protrusions used are shown in their placement on the strings in FIG. 1(c) where they engage the underside of the housing with the strings 5 oriented as in FIG. 1(c). The lowermost strings 13 in FIG. 1(c) are single strings while the strings 15 are double strings and the strings 17 are triple strings.

Between the protrusions is a permanent magnet 19 (see dotted lines in FIG. 1(b)) used to hold the housing in place on the metallic strings whether on a grand or upright piano. Since the unit is used with its top side facing a user, as seen in FIG. 1(a), lines 21 may be marked or molded in the body of the housing 1 that can be visually aligned with the lower strings over which it is placed as an added verification that there is proper placement of the housing on the piano strings.

The housing 1 is a completely self-contained device that runs on a self contained power source consisting of a battery. There are no connecting wires from the housing to interfere with the vibrations of the strings. The housing is also small enough to fit into a user's pocket and accurate enough to be within one "cent" or 1/100.sup.th of a musical half-step.

FIG. 2 is a diagram of the detected signals as observed on an oscilloscope. A coil of wire 21 in the pickup units 9, shown in FIG. 1(a), is wrapped around a magnetic core and used to detect the vibration of ferrous objects, here strings, to produce a tuning signal. This type of pickup unit is commonly used in electric guitars as a "pickup." If this pickup is brought near a vibrating string, an electric current is induced in the coil that mimics the motion of the string. By using this type of pickup rather than a microphone, there can be no background noise, and each individual string may have its own dedicated pickup and be tuned independently even though all of the strings are vibrating together. Due to the standard spacing of piano strings, which may be in groups of one, two or three strings, an extra fourth pickup is necessary to detect some arrangements as shown in FIGS. 1(a)and 1(c).

The detected, or tuning, signal can be amplified by an amplifier 23 and viewed on a conventional oscilloscope, not shown. If the pickup is placed near the middle of a string, a sine wave is observed with a frequency equal to the fundamental frequency of the vibrating string. As the pickup is moved toward the end of the string, some harmonics are added which make the wave appear more complex. These overtones can be removed with a frequency controlled low-pass filter 25. If this signal is passed through a zero crossing detection circuit 27, it will become a square wave 29 with a period equal to the fundamental period of the string vibration.

Audio frequencies are relatively low and their waves are hard to count accurately without encountering the error of a fractional and incomplete wave. Frequency counting is therefore, not a viable solution for frequency measurement. A much more accurate method to be used is to measure the period of the wave or the time that lapses during one complete cycle. Ultra-high frequency oscillators are very common, small and quite inexpensive today. These oscillators work based on the oscillation of a tiny piezoelectric crystal and produce square waves with frequencies of many millions of cycles per second with extremely high accuracy. Clearly, if you can count the number of oscillator waves generated during a single audio wave, you can obtain a super precise value for the period and thus the pitch of the note. Thus, the tuning signal is processed to determine a first value for a tuning period of the tuning signal.

To effect this desired result, a common Intel 82C54 programmable interval timer chip composed of three independent 16-bit counters that handle frequencies up to 10 MHz is used. Each of the chip counters has three connections: clock, gate and output as is illustrated in the block diagram of FIG. 3. The clock input is the signal 29 that is counted. The gate input signal B can have two different functions depending on the mode selected for the counter. Signal B is usually for gating the clock and allowing the counter to start counting the incoming pulses. Signal B can also be used as a trigger if the counter is programmed to operate in "one-shot" mode. The output is simply a signal to indicate that the counter has reached a preset value programmed into it. The first thing to do is fool the first counter 30 and use the audio square wave 29 from the zero crossing detector as the clock signal. This counter is set up as a one-shot. In one-shot mode the counter waits for a trigger pulse on its gate input and then counts clock inputs until the count reaches a preset value. The output is activated on the first rising edge of the clock input that occurs after a trigger pulse. The output is deactivated on the first rising edge of the clock input after the preset number of "ticks" is reached. If the preset value of the counter is set to "1" we obtain an output pulse with a duration equal to exactly one fundamental wave period.

The second chip counter 31 is programmed to operate in simple count-up mode. The output from the first counter 30 is sent to the gate of the second counter 31 and a 10 MHz oscillator 35 to the clock input, counting the clock pulses during the one-period pulse. The second counter 31 counts the number of high-frequency pulses that occur during one period of vibration of the piano string. This value can be read by a microcontroller 37 and the exact period is now known. For example, for the musical note A440 (440 Hz) a correct equal temperament value for its period in terms of a 10 MHz clock would be 10,000,000 divided by 440 or 22,727 ticks. This value for a baseline period can be permanently stored in memory and used to compare and evaluate the measured signal. Thus, the first value for the tuning period of the tuning signal is compared to a second value for a baseline period of a musical note to evaluate the tuning signal.

Modem musical instruments are tuned to a standard known as equal temperament. The correct frequencies for all the notes of a piano can be determined by the equation: ##EQU1##

where N =number of a note on the piano with the lowest A being 0 and .function..sub.N =correct frequency for note N.

The period of a wave is simply the reciprocal of its frequency, or ##EQU2##

where .function..sub.c =clock frequency or 10 MHz.

Correct periods are thus calculated for all 88 notes on the piano and stored in EEPROM memory for comparison. Unfortunately for the lowest notes on a piano the periods become quite large (