Note: Descriptions are shown in the official language in which they were submitted.
CA 02298386 2000-02-11
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
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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.
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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
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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.
CA 02298386 2000-02-11
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
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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
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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,
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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.
