CA2298386A1 - Apparatus for playing stored music through an audio cassette player - Google Patents

Abstract

A self-contained and self-powered MP3 music storage device that may be used in place of an audio cassette and controlled by an unmodified audio cassette player. The device senses the direction and speed of rotation of the drive shafts of the audio cassette player to determine whether to play, fast forward, fast rewind, or stop playing music stored in the device and provides the appropriate sound signals to the audio cassette player through a magnetic head coupled to the tape playback head of the audio cassette player. To the audio cassette player the device appears to be a conventional audiocassette.

Description

APPARATUS FOR PLAYING STORED MUSIC
THROUGH AN AUDIO CASSETTE PLAYER
FIELD OF THE INVENTION
This invention relates to the field of devices designed to adapt older audio player technologies to new music storage formats.
BACKGROUND OF THE INVENTION
ISO-MPEG Audio Layer-3 (commonly referred to as "MP3") is an audio coding algorithm currently used in portable, lightweight digital music players such as the Diamond Multimedia Rio PMP300 player. Such players are smaller than an audio cassette, yet hold up to 60 minutes of digital sound. Data representing the recorded music is stored in flash memory so that the players have no moving parts.
It has not until now been possible to obtain the advantages of MP3 recording without purchasing a player or using the MP3 algorithm on a general purpose computer. In particular, audio cassette players, which are in widespread use and are inexpensive, cannot record or play MP3 encoded sound directly.
Rather that replace the huge existing base of audio cassette players with new hardware employing the technology used in portable MP3 players, it would be preferable to offer consumers the choice of retaining their existing sound equipment while enjoying the advantages of MP3 recorded sound.
Devices are available to allow portable CD players to be connected to audio cassette players without modification of either. However, the controls on the CD players must still be used, leading to some inconvenience, especially in the case of automobile cassette player systems. Ideally, the existing controls of the audio cassette players should be the only controls needed to operate the add-on sound source, such as the MP3 player.
SUMMARY OF THE INVENTION
The present invention is directed in one aspect to providing an MP3 encoded sound storage and play-back device that can be contained within an audio cassette case (an "MP3 cassette") so that the entire device may be inserted into an audio cassette player in place of an conventional audio cassette.
The device is completely self-contained, self-powered, and controlled by a completely unmodified audio cassette player. The device senses the rotation of the drive shafts of the audio cassette player to determine whether to play, fast forward, fast rewind, or stop the playing of MP3 encoded musical selections. A
magnetic head is used to couple the decoded sound signal to the tape playback head of the audio cassette player so that to the audio cassette player the device appears to be a conventional audiocassette.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is functional block diagram of the electronics of a preferred embodiment of the MP3 cassette.
Figure 2 is a composition of views illustrating the mechanical construction of the MP3 cassette.
Figures 3 and 4 are additional views of the exterior and interior, respectively, of the MP3 cassette.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
A preferred embodiment of the MP3 cassette is illustrated in Figures 1 - 4.

The following is a table listing the reference numerals used in Figure 2 for the various parts of the MP3 cassette and briefly describing those parts:
1 bottom of case of MP3 cassette 2 top of case of MP3 cassette 3 batteries 4 screws holding top and bottom of case together 5 contacts 6 spring contact, together with contacts 5 forms a switch, such that the switch is on if magnetic head 9 is pressed and reset if magnetic head 9 is released 7 magnetic head printed circuit board 7 8 push knob for adjusting position of magnetic head 9 9 magnetic head assembly 9 10 DC jack for charger 11 light (lens) for LED

12 battery voltage status LED

13 infrared LED printed circuit boards 14 infrared LEDs 15 photo diode printed circuit boards 16 photo diodes 17 main printed circuit board 18 data input and output terminals 19 wheels The following is a description of the functions and features of the functional blocks of Figure 1:
PC Interface - A communication port to allow connection of a personal computer to the MP3 cassette. Data in MP3 format may be downloaded to the flash memory of the MP3 cassette through this port in a conventional manner, if the flash memory is RAM.
Play Status Detect - Detects the operating mode of the cassette player by sensing the speed and direction of rotation of wheels.
The light path between the infrared LEDs 14 and photodiodes 16 passes through cogs on the wheels 19 providing signals to the microprocessor allowing the microprocessor to determine the direction and speed of the wheels 19. Direction can be determined by determining which of wheels 19 is being driven and speed from rate at which the light path between the LED 14 and associated photodiode 16 adjacent the driven wheels 19 is interrupted by the cogs on that wheel.
Microprocessor - The control center to all the circuitry of the MP3 cassette. It is a Microchip PIC17C74B. Controls the MP3 decoding using play status detected from rotation of wheels 19.
Flash Memory - Where the data in MP3 format is stored. It is a memory product made by Samsung Semiconductor 2KM29u256T.
MP3 Decoder - Performs the compression and expansion of the data stored in MP3 format in the flash memory. Consists of a PL7230MD
and associated components.
D/A Conversion - Converts digital signals to analog sound signals in a conventional manner.
Sound Signal Amplifier - The power amplifier (a HT9274), amplifies the left and right channel audio coming out from the MP3 decoder.
Battery Low Indication - Flashes to warn the user when battery is nearly discharged.
Power Management Maintains minimum operating current to enhance the battery life when the MP3 cassette is in idle mode.

The MP3 cassette described herein may be used in a conventional cassette player by inserting the MP3 cassette into the cassette player in the same manner as a conventional cassette tape is inserted so that the wheels 19 will be rotated by the 5 drive shafts of the cassette player when the cassette player is playing, fast forwarding or rewinding. Of course, in the MP3 cassette there is no magnetic tape wound on the wheels (which correspond to the reels of a conventional cassette tape).
Instead the MP3 cassette detects the rotation of the wheels 19 and provides the appropriate signal to a magnetic head 9 that couples with the tape head of the cassette player. The manner in which this magnetic coupling is accomplished is that conventionally used in devices to couple a portable CD player to a car cassette player. However, in this case the cassette player controls are fully functional and no controls are needed on the MP3 cassette, which generally corresponds to the portable CD
player. To the user, the cassette player seems to be playing an ordinary cassette tape, although the controls respond with very little delay and the sound quality is superior.
More specifically, if the "PLAY" key on the cassette player is then pressed, one of the wheels 19 will by rotated by a drive shaft of the cassette player (whichever shaft is driven when a conventional cassette is being played). The microprocessor will, based upon which wheel is rotating and its speed, control the other circuitry to begin decoding the music stored in the memory in MP3 format, decompressing it, converting to a two channels of analog signals, amplifying each channel, and convert the electrical signal into magnetic signal through magnetic head 9. Such decoding, decompressing, and converting is conventionally used in currently available MP3 players and such amplification and magnetic coupling is used in devices for connecting portable CD players to cassette players. The MP3 cassette uses such conventional elements in combination.
When "STOP" key on the cassette player is pressed, the MP3 cassette will sense that the rotation of the driven wheel has stopped and stop the transmission of the music signal to the magnetic head.
When "FAST FORWARD" key on the cassette player is pressed, the MP3 cassette will sense the higher forward speed of the rotation of the driven wheel and jump to the starting point of the next music selection, stop there, and wait 5 seconds. If the user to press "STOP" and "PLAY", the next selection will begin playing. If the user does not press "STOP" within 5 seconds, then the MP3 cassette will jump ahead another selection and so forth until the user presses "STOP" and "PLAY".
When "FAST BACKWARD" key on the cassette player is pressed, the MP3 cassette will sense the high speed rotation of the other wheel and jump to the starting point of the previous selection and stop there wait for 5 seconds. If the user presses "STOP" and "PLAY" then that selection will be played. Otherwise the MP3 cassette will jump back one more selection and wait the other 5 seconds and so forth until the user presses "STOP" and "PLAY" .
When "PAUSE" key on the cassette deck player is pressed, the driven wheel on the cassette deck will stop rotating, such that the MP3 cassette will sense the stop rotation of the wheel and stop the playing of music.
The MP3 cassette can be provided with ROM or RAM memory for storing MP3 encoded music. If ROM is used, then the stored music cannot be changed, but if RAM memory is used, then the 3o stored music can be changed by download MP3 encoded music from a computer using the PC interface in a conventional manner.
Two "AAA" type rechargeable batteries are used to power the MP3 cassette. A charge is expected to last for around 10 hours. External power can also be used through DC jack 10.
A low-battery detection circuit is also provided such that when battery is close to becoming discharged, a beep tone will be heard during music playback, and the LED 12 will flash to warn the user that battery need to be recharged. Such circuits are conventional.
The general advantages of MP3 cassette as compared to conventional tape are that:
1. more music selections can be stored;
2. fidelity of the sound reproduction is close to CD quality;
3. music can be easily pre-edited;
4. no "tape jams" can occur; and 5. forward and backward (rewind) access to music selections are much faster.
Other modifications will be apparent to those skilled in the art and, therefore, the invention is defined by the claims. For example, it should be apparent from the foregoing that controlling of the playback of the MP3 cassette by the controls of a conventional cassette player is a special case of a more general concept that could be applied to other recorded music storage devices. For example, a modified portable CD
player could be controlled in the same fashion. The cassette player controls could replace or override the controls provided by a conventional portable CD player. The advantage of this would be most apparent if such a device were connected to a car cassette. It is much more convenient and safer to use the controls of a built-in car cassette player than to attempt to control a portable CD player using its control. Using the information disclosed herein it should be clear to those skilled in the art that the only difference between using the MP3 cassette to store and play MP3 music and using a modified version to control a CD player would be in the functional block labeled MP3 decoder. In place of the MP3 decoder, those skilled in the art will understand that circuitry interfacing the MP3 cassette with a conventional portable CD player would be needed and would control playback of selections from the CD player and would provide appropriate digital data to the MP3 cassette. Of course, the interface circuitry could alternatively obtain analog sound channel signals from the CD player.
It should further be noted that the MP3 cassette described above uses the interruption of light paths by cogs on wheels driven by the drive shafts of the cassette player to obtain the data necessary to control the playing of music selections. Other means for obtaining such data will occur to those skilled in the art related of obtaining rotational speed and direction of rotating shafts. For example, magnetic rather than light sensors may be employed.
Further, the encoding method assumed in the above description is MP3. However, it should be clear to those skilled in the art that any encoding method may be used in the MP3 cassette device described above with minor changes understood by those skilled in the art. The device is described as the "MP3 cassette" for convenience and because the preferred embodiment described in detail herein used the MP3 encoding method.

Claims (10)

1. A music storage device for playing stored encoded music though an audio cassette player, the device comprising:
a play status detector for detecting the configuration of the controls of the audio cassette player;
a memory for storing encoded music data;
an decoder for decoding music data stored in the memory;
D/A converter for converting data representing the decoded music into at least one analog signal;
an amplifier for amplifying the analog signal;
a magnetic head for magnetically coupling the amplified analog signal to the tape play head of the audio cassette player; and a microcontroller for controlling the selective playback of the music stored in the memory based upon the play status detector.

2. The device of claim 1, contained within a case that is physically interchangeable with a conventional audio cassette and playable in a conventional audio cassette player.

3. The device of claims 1 or 2, wherein the play status detector senses the rotational direction and rotational speed of the reel drive shafts of the cassette player to determine the configuration of the controls of the audio cassette player.

4. The device of claim 3, wherein the play status detector comprises:
two wheels mounted in the case so that when the device is inserted into a cassette player each wheel axially mates with and is driven by a discrete one of the reel drive shafts, each wheel having cogs about its circumference protruding radially; and two light source / light sensor pairs, each pair positioned adjacent a discrete one of the wheels so that the light emitted by the light source follows a path that passes the circumference of the wheel and is sensed by the light sensor, but the light path is interrupted by the cogs if the wheel turns, whereby the configuration of the controls of the cassette player may be determined from signals produced by the light sensors, the direction setting of the controls determined from which of the light sensors produces a varying signal and the speed setting of the controls determined from the rate at which the varying signal varies.

5. The device of any of the foregoing claims, wherein the encoding method is ISO-MPEG Audio Layer-3.

6. An apparatus for connecting a music storage device to a conventional audio cassette player, the apparatus comprising:
a play status detector for detecting the configuration of the controls of the audio cassette player;
a magnetic head for magnetically coupling an analog signal obtained from the music storage device to the tape play head of the audio cassette player; and a microcontroller for controlling the selection playback of the music stored in the music storage device based upon the configuration of the controls of the audio cassette player received from the play status detector.

7. The apparatus of claim 6, contained within a case that is physically interchangeable with a conventional audio cassette.

8. The apparatus of claims 6 or 7, wherein the play status detector senses the rotational direction and rotational speed of the reel drive shafts of the cassette player to determine the configuration of the controls of the audio cassette player.

9. The apparatus of claim 8, wherein the play status detector comprises:
two wheels mounted in the case so that when the device is inserted into a cassette player each wheel axially mates with and is driven by a discrete one of the reel drive shafts, each wheel having cogs about its circumference protruding radially; and two light source / light sensor pairs, each pair positioned adjacent a discrete one of the wheels so that the light emitted by the light source follows a path that passes the circumference of the wheel and is sensed by the light sensor, but the light path is interrupted by the cogs if the wheel turns, whereby the configuration of the controls of the cassette player may be determined from signals produced by the light sensors, the direction setting of the controls determined from which of the light sensors produces a varying signal and the speed setting of the controls determined from the rate at which the varying signal varies.

10. The apparatus of any of claims 6 through 9, wherein the music storage device is a portable CD player.