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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to enunciators for portable data
collection terminals, and in particular to a voice prompt system for a
portable data collection terminal.
2. Description of Related Art
A data collection terminal 100 typically has an enclosure 101 housing a
display 103, such as a liquid crystal display (LCD) 103, a keypad 102 for
entering data, and an enunciator 108 for audible feedback. Optionally, a
bar code scanning device, such as a wand 104, may be connected to or
integral in data collection terminal 100 for entering bar code data 106.
Data collection terminal 100 is typically battery powered using one or
more battery cells. To conserve battery power, wand 104 may be pulsed or
contain a switch 105 that turns on wand 104 and terminal 100 only while
switch 105 is activated.
A typical portable data collection terminal 100 is small and lightweight
and is easily held in the hand of the operator during use. Data is
collected and stored in terminal 100 as it is entered by the user by
either pressing the appropriate keys on keypad 102 or by "scanning" bar
code 106 with wand 104.
To "scan" bar code 106 using wand 104, an operator presses switch 105 and
then passes wand 104 over bar code 106 in a linear direction substantially
perpendicular to the bars. The scanned bar code is decoded by decoder
computer 201 (FIG. 2) and stored in nonvolatile read/write memory 202.
Enunciator 108 typically beeps after a bar code scan to inform the user
that the bar code has been decoded properly.
Decoder computer 201 typically includes a central processing unit (CPU)
214, volatile read/write memory 213, typically static random access memory
(SRAM), and nonvolatile read only program memory 215, typically erasable
programmable read only memory (EPROM). EPROM 215 contains the firmware
that is executed by CPU 214 and that tells CPU 214 what to do. Herein,
firmware, program, and software are used interchangeably.
Depending on the process running in terminal 100, (FIG. 2) additional
prompts and messages may be displayed on LCD 103 to direct the operator to
take various actions such as "Enter Quantity:" or "Enter Item:". In
addition, beep tones of various frequencies or a series of beeps may be
used to prompt the user to take various actions. However, in many
situations, it is cumbersome to read LCD 103, count the beeps, or listen
for certain tones while scanning bar codes. Further, data collection is
more efficient if it can be done without referring to LCD 103 for the next
action to be taken.
In a data collection mode, visual prompts are displayed on LCD 103 to
inform the user of the information to be entered. This information may be
entered by either scanning one or more bar codes using bar code scanner
104 or keying in the information using keypad 102. As the data is
collected, the data is stored in nonvolatile read/write memory 202. When
data collection is complete, portable data collection terminal 100 is
connected to host computer 210 through input/output (I/O) interface 209.
Portable data collection terminal 100 is then put into data upload mode
and the collected data is transmitted to host computer 210.
SUMMARY OF THE INVENTION
In accordance with the principles of this invention, a portable data
collection system includes a portable data collection terminal with a
voice prompt circuit, and optionally a bar code scanning device, such as a
wand. The portable data collection terminal of this invention is similar
in size and performs the same data collection functions as prior art
portable data collection terminals but adds voice prompts for improved
functionality, flexibility, and ease of use.
When data is entered from either a keypad or a bar code scanner, which are
examples of data input means, or when the operator needs to be prompted to
take a particular action, the voice prompt circuit of the portable data
collection terminal is activated to provide an oral voice prompt to the
user. The oral voice prompt is a significant improvement over the beeps,
tones, and visual messages provided by prior art portable data collection
terminals.
In one embodiment, the portable data collection terminal of this invention
includes a voice prompt circuit a data input means, and a decoder
computer. When the portable data collection terminal of this invention is
turned on, power is delivered to the decoder computer from a power supply.
The decoder computer runs a program that displays messages on a display of
the portable data collection terminal and prompts the user using the voice
prompt circuit of this invention.
The user selects the mode of operation of the portable data collection
terminal by using the data input means, which can include either a keypad
or a bar code scanner. The signal generated in response to either pressing
a key on the keypad or scanning a bar code using the bar code scanner is
processed by the decoder computer.
For example, when the bar code scanner is scanned across a bar code, the
output voltage from the bar code scanner is sent to the decoder computer.
The decoder computer decodes the scanned bar code and stores the
information in a nonvolatile read/write memory in a manner well-known to
those skilled in the art.
After the scanned bar code is decoded, for example a bar code representing
"4983", the decoder computer automatically activates the voice prompt
circuit and addresses the oral messages stored in the voice prompt circuit
and sends the necessary commands to the voice prompt circuit to retrieve
and play the oral messages. Thus, the voice prompt circuit responds with
the oral voice prompt "four, nine, eight, three," or in another mode
"Enter quantity" or "Enter stock number". If the portable data collection
terminal is configured as a bar code verifier, the terminal responds with
oral qualitative statements describing the characteristics of the scanned
bar code. A feature of the voice prompt circuit is simple recording by the
user of oral messages used to generate voice prompts. This allows the user
to customize voice prompts for a specific application.
As data is collected, the user is prompted by the information on the
display, an oral voice prompt from the voice prompt circuit of this
invention, or both. By entering data using the bar code scanner and using
voice prompts from the voice prompt circuit for feedback, the user need
not refer to the display to determine the next course of action and is
therefore more productive. Thus, voice prompts provide the ability to
combine visual messages and oral voice prompts. Further, the oral voice
prompts generated by the voice prompt circuit provide the convenience and
speed of not having to look at the display when using the portable data
collection terminal of this invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a typical prior art portable data collection terminal
with a bar code scanner attached.
FIG. 2 is a block diagram of a typical prior art portable data collection
terminal.
FIG. 3 illustrates a portable data collection terminal of this invention
with a bar code scanner attached and voice prompt capability.
FIG. 4A is a block diagram of the portable data collection terminal of this
invention with an external bar code scanner.
FIG. 4B is a block diagram of the portable data collection terminal of this
invention with an internal bar code scanner.
FIG. 4C is a block diagram of the portable data collection terminal of this
invention with a wireless bar code scanner.
FIG. 5 is a block diagram of the voice prompt circuit in one embodiment of
the portable data collection terminal of this invention.
FIG. 6 is a wiring diagram of the voice prompt circuit of FIG. 5.
FIG. 7 is a flow chart illustrating the steps in a program that is executed
by the CPU in the portable data collection terminal to record a voice
prompt.
FIG. 8 is a timing diagram illustrating events (control signals) vs. time
for a control sequence in the flowcharts in FIGS. 7 and 12.
FIG. 9 is a timing diagram illustrating events vs. time for a control
sequence in the flowchart in FIG. 7.
FIG. 10 is a timing diagram illustrating events vs. time for a control
sequence in the flowchart in FIGS. 7 and 12.
FIG. 11 is a timing diagram illustrating events vs. time for the flowchart
in FIG. 7.
FIG. 12 is a flow chart illustrating the steps in a program that is
executed by the CPU in the portable data collection terminal to play a
voice prompt.
FIG. 13 is a timing diagram illustrating events vs. time for a control
sequence in the flowchart in FIG. 12.
FIG. 14 is a timing diagram illustrating events vs. time for the flowchart
in FIG. 12.
DETAILED DESCRIPTION
In accordance with the principles of this invention, a portable data
collection system includes a portable data collection terminal 300 with a
voice prompt circuit, and optionally a bar code scanning device, such as
wand 304. Portable data collection terminal 300 is similar in size and
performs the same data collection functions as prior art portable data
collection terminals but adds voice prompts for improved functionality,
flexibility, and ease of use.
When data is entered from either a keypad 302, or a bar code scanner 304,
or when the operator needs to be prompted to take a particular action, a
voice prompt circuit is activated to provide an oral voice prompt to the
user. The oral voice prompt provided by portable data collection terminal
300 is a significant improvement over the beeps, tones, and visual
messages provided by prior art portable data collection terminals.
While in FIG. 3, bar code scanner 304 is connected by a cable to portable
data collection terminal 300, this is only illustrative of a bar code
scanner and is not intended to limit the invention to a cabled wand. One
skilled in the art will appreciate that other types of bar code scanners
and data collection devices such as CCD scanners, laser scanners, and
magnetic strip readers may serve as data input means to portable data
collection terminal 300. Bar code scanner 304 can also be built as an
integral part of portable data collection terminal 300. (FIG. 4B)
Alternatively, bar code scanner 304 can be a cordless wand that transmits
data to portable data collection terminal 300. (FIG. 4C) For example, the
cordless wand, described in copending and commonly assigned U.S. patent
application Ser. No. 07/958,638, entitled "LOW POWER CORDLESS BAR CODE
SCANNER" of H. Worthington et al. which is incorporated herein by
reference in its entirety, could be utilized with portable data collection
terminal 300.
Components 104, 103, 102 and bar code 106 of portable data collection
terminal 100 are, in this embodiment, the same as components 304, 303, 302
and bar code 306, respectively of portable data collection terminal 300.
In one embodiment, portable data collection terminal 300 of this invention
includes a voice prompt circuit 408 (FIG. 4A), keypad 302, display 303,
power supply 403, optionally bar code scanning device 304, nonvolatile
read/write memory 402 for data storage, and a decoder computer 401 that
includes central processing unit 414, volatile read/write memory 413, and
nonvolatile read only program memory 415. When portable data collection
terminal 300 of this invention is turned on, power is delivered to decoder
computer 401 from power supply 403. Power supply 403 is driven by either
an internal battery 404 or by an external power source 412. Again
components 401, 402, 403, 404, 409, 413, 414, 415 of portable data
collection terminal 300 are, in this embodiment, the same as components
201, 202, 203, 204, 209, 213, 214 and 215 respectively of portable data
collection terminal 100.
Decoder computer 401 runs a program that displays messages on display 303
and can prompt the user using voice prompt circuit 408 as well. The user
selects the mode of operation by either pressing a key on keypad 302 or by
scanning bar code 306 using bar code scanner 304. The signal generated in
response to either pressing a key on keypad 302 or scanning bar code 306
is processed by decoder computer 401, as described more completely below.
In a data collection mode of terminal 300, when bar code scanner 304 is
scanned across bar code 306, the output voltage from bar code scanner 304
is representative of bar code 306. This output voltage is sent to decoder
computer 401 which decodes bar code 306 and stores the information in
nonvolatile read/write memory 402 in a manner well-known to those skilled
in the art.
In this embodiment, decoder computer 401 uses programs stored in EPROM 415
to decode the voltage generated by scanning bar code 306. The programs
stored in EPROM 415 are similar to prior art programs except the programs
include the capability to send addresses and control signals, sometimes
referred to as "commands" to voice prompt circuit 408 to generate the
desired oral voice prompt. The modification required to the prior art
programs to include voice prompt capability will be apparent to those
skilled in the art in view of the following disclosure.
Voice prompt circuit 408 can be activated at any time. Voice prompt circuit
408 is typically automatically activated in response to data input such as
a user pressing a key on keypad 302 or scanning bar code 306. For example,
a user may press key "1" on keypad 302 and in response, the number "one"
is spoken back by voice prompt circuit 408 in the user's language to
confirm that key "1" was pressed. Alternatively, after a multi-digit
number such as "2398" is entered by the user and the "Enter" key is
pressed, voice prompt circuit 408 responds with the oral voice prompt of
either "two thousand nine hundred and eight" or "two, three, nine, eight"
depending on the programming of portable data collection terminal 300.
After scanning a bar code of the number "4983," voice prompt circuit 408
responds with the oral voice prompt "four, nine, eight, three," or in
another mode "code thirty-nine, four, nine, eight, three" to identify the
type of code and the data stored in the bar code. If portable data
collection terminal 300 is configured as a bar code verifier, terminal 300
responds with qualitative oral statements describing the characteristics
of the scanned bar code.
To assist the user with data collection, voice prompt circuit 408 can
respond to scanned or entered data with voice prompts such as "Enter item
number", "Scan user ID", or "Bad Item Number, Re-enter". Any message that
can be spoken can be stored in voice prompt circuit 408. The only
limitation is the length of time of the message.
As data is collected, the user is prompted by the information on display
303, the oral voice prompt from voice prompt circuit 408, or both. By
entering data using bar code scanner 304 and using voice prompts from
voice prompt circuit 408 for feedback, the user need not refer to display
303 to determine the next course of action and is therefore more
productive. Thus, voice prompts provide the ability to combine visual
messages and oral voice prompts. Further, the oral voice prompt generated
by voice prompt circuit 408 provides the convenience and speed of not
having to look at the display when using portable data collection terminal
300. Voice prompts may also be used to alert the user in the case of an
error or incorrectly entered data.
Voice prompt circuit 408 can record and playback any message spoken to it.
To facilitate play back of the messages in any desired sequence, each
recorded message is assigned an index which is subsequently used to access
the recorded message, as explained more completely below. Voice prompt
circuit 408, in one embodiment, can record up to 40 seconds of indexed
messages that can be combined in any order during playback.
FIG. 5 is a more detailed block diagram of one embodiment of voice prompt
circuit 408. In this embodiment, two direct analog storage integrated
circuits are used to store the up to 40 seconds of recorded messages. One
integrated circuit is configured as master sound circuit 505 and the other
as slave sound circuit 504. Each sound circuit can store 20 seconds of
recorded messages. Only one sound circuit can playback or record messages
at a time. After master sound circuit 505 has been filled with 20 seconds
of messages slave sound circuit 504 is used to store the next 20 seconds
of messages. An input buffer 503 is provided to allow decoder computer 401
to monitor the status of sound circuits 504 and 505 to determine when a
voice prompt has terminated playing.
An electret condenser microphone 307 is attached to the microphone input
terminal of master sound circuit 505 to allow recording of custom messages
by the user. A microphone input circuit, which is described more
completely below, includes a bias network that converts audio frequency
waves from microphone 307 into electrical signals which are further low
pass filtered and preamplified by master sound circuit 505. An AGC
(Automatic Gain Control) circuit in master sound circuit 505 is utilized
to control the gain of the preamplifier. The AGC circuit reduces
amplification on loud sounds to eliminate clipping and increases
amplification on soft sounds to make them louder.
The signal from the preamplifier is amplified and sampled by master sound
circuit 505 and then stored in one of sound circuits 504 or 505.
Specifically, a nonvolatile CMOS analog storage array using EEPROM
technology is provided in sound circuits 504 and 505 to reduce power
consumption and lower cost. The incoming signal is sampled at 125 .mu.sec
intervals and sequentially stored in the nonvolatile CMOS analog storage
array. Since this array is an EEPROM structure, no external power is
required to retain the signals once they are stored in the array. While in
this embodiment the nonvolatile storage means is a CMOS EEPROM structure,
those skilled in the art will appreciate that a variety of volatile and
nonvolatile storage means can be utilized. The storage means selected
depends on the sound circuits used, power constraints and cost, for
example.
Decoder computer 401 has control over the various modes of operation of
sound circuits 504 and 505. The operational modes for voice prompt circuit
408 are record and playback. To save battery power, a power down mode of
voice prompt circuit 408 is selected by decoder computer 401 when no
recording or playback functions are desired.
Master sound circuit 505 includes an output filter that reduces sampling
frequency noise and smooths the output waveform. The output signal from
master sound circuit 505 is amplified by amplifier circuit 507 to about
250 mW RMS. The amplified signal from amplifier circuit 507 directly
drives an enunciator 308 with an impedance of 8 ohms or greater. An
earphone 508 may also be used instead of, or in addition to, enunciator
308 for monitoring the audio output. For example, earphone 508 is directly
connected to the speaker output pin of master sound circuit 505.
As described more completely below, voice prompts are generated by voice
prompt circuit 408 in response to decoder computer 401 writing two bytes
of information into output registers 501 and 502. First, the address of
the voice prompt is loaded and then the play command. Registers 501 and
502 store the addressing information used to select one oral message from
the plurality of oral messages stored in sound circuits 504 and 505.
Registers 501 and 502 also store operational mode commands for sound
circuits 504 and 505, such as play/record (P/R), power down (PD), and chip
enable (CE).
Messages are recorded in portable data collection terminal 300 by adding
microphone 307. No additional hardware or software is required to record
the messages. In one method of recording a message, the user selects a
number for the message by pressing the appropriate keys on keypad 302, and
then presses a predetermined key on keypad 302 to begin recording. CPU 414
issues a beep from enunciator 308 when CPU 414 is ready to record. The
user speaks into microphone 307 and the message is recorded by sound
circuits 504 and 505. When the length of time allotted for the message has
passed, CPU 414 issues another beep from enunciator 308 and the recording
process stops.
CPU 414 uses the number entered by the user to index the message. The
message stored in sound circuits 504 or 505 can be played back in any
order to generate a voice prompt. For example, if message #045 was
"Enter", message #029 was "Data" and message #073 was "Quantity" the voice
prompt "Enter Data" is created by playing message #045 followed by a short
delay then message #029. Similarly, the voice prompt "Enter Quantity" is
generated by playing message #045 followed by a short delay then message
#073. Thus, many voice prompts may be created from a selected group of
messages. The voice prompts are created by providing an appropriate
program in EPROM 415 for execution by CPU 414. Custom voice prompts may be
recorded by the user or created from recorded messages.
Herein, a "message" is one indexed oral entry that is stored in sound
circuits 504 and 505. A "voice prompt" is the playback of a "message" or a
group of "messages" by CPU 414 in response to instructions stored in EPROM
415. Thus, a customized voice prompt can be a single message. However,
more flexibility is generally provided by storing a plurality of messages
in sound circuits 504 and 505 and using various combinations of the stored
messages to create a plurality of voice prompts.
One embodiment of the voice prompt circuit 408 of portable data collection
terminal 300 is illustrated in more detail in FIG. 6. Registers 501 and
502 are eight-bit registers 6U4 and 6U5. One eight-bit register integrated
circuit suitable for use in this inventions is sold by Texas Instruments
as Part No. 74HC273. Eight-bit registers 6U4 and 6U5 have I/O addresses
0005H and 0006H respectively in the I/O address space of decoder computer
401.
A command or a message address, collectively referred to as data, is loaded
into eight-bit register 6U5 when CPU 414 writes to I/O address 0005H and a
command or a message address is loaded into eight-bit register 6U4 when
CPU 414 writes to I/O address 0006H. Specifically, the I/O address 0005H
from CPU 414 is decoded as a low signal on line CS5 during an I/O cycle
and I/O address 0006H from CPU 414 is decoded as a low signal on line CS6
during an I/O cycle. One skilled in the art will appreciate that the logic
levels and logic gates described herein are only illustrative and the
invention can be implemented using both other logic gates and other logic
levels.
Line CS5 is connected to a first input terminal of logic OR gate 6U9A. The
other input terminal of logic 0R gate 6U9A is driven by CPU 414 signal
-WR. The output terminal of logic OR gate 6U9A is connected to terminal
CLK of eight-bit register 6U5.
Line CS6 is connected to a first input terminal of logic OR gate 6U9B. The
other input terminal of logic 0R gate 6U9B is driven by CPU 414 signal
-WR. The output terminal of logic OR gate 6U9B is connected to terminal
CLK of eight-bit register 6U4.
During the write, the I/O address of the register to be written to is
output onto the address bus (not shown) which is decoded to drive the
signal on one of lines CS5 or CS6 low. The signal on line --WR is driven
low and data is output onto data bus lines D0-D7 from CPU 414. The data is
loaded into either 8-bit register 6U4 or 8-bit register 6U5 by the rising
edge of the signal on write line -WR which is driven by CPU 414. Bits 4
through 7 of 8-bit register 6U5 drive address input terminals A1 through
A4 of both sound integrated circuits 6U6 and 6U10. Bits 0 through 2 of
8-bit register 6U4 drive address input terminals A5 through A7 of both
sound integrated circuits 6U6 and 6U10.
Bit 3 of 8-bit register 6U4 drives inverter 6U8B which in turn drives chip
enable input terminal CE of sound integrated circuit 6U10. Bit 5 of 8-bit
register 6U4 drives inverter 6U8C which in turn drives chip enable input
terminal CE of sound integrated circuit 6U6 through inverter 6U8C. Command
CE for sound integrated circuit 6U10 is issued when a logic one value is
loaded into bit 3 of eight-bit register 6U4. CPU 414 issues command CE for
sound integrated circuit 6U6 by loading a logic one value into bit 5 of
8-bit register 6U4.
Bit 6 of 8-bit register 6U4 drives inverter 6U8D which in turn drives power
down input terminals PD of sound integrated circuits 6U6 and 6U10 and
input terminal CD of audio amplifier 6U7. CPU 414 issues command PD to
sound integrated circuits 6U6 and 6U10 and audio amplifier 6U7 by loading
a logic zero value into bit 6 of 8-bit register 6U4.
Bit 7 of 8-bit register 6U4 drives inverter 6U8E, which in turn drives
play/record input terminal P/R of sound integrated circuits 6U6 and 6U10.
CPU 414 issues the play command to sound integrated circuits 6U6 and 6U10
by loading a logic zero value into bit 7 of 8-bit register 6U4. The record
command is issued to sound integrated circuits 6U6 and 6U10 when CPU 214
loads a logic one value into bit 7 of 8-bit register 6U4.
Input buffers 6U1A and 6U1B allow CPU 414 to monitor the playback status of
sound integrated circuits 6U6 and 6U10. Input buffer 6U1A is driven by
sound integrated circuit 6U6 signal EOM1. Input buffer 6U1B is driven by
sound integrated circuit 6U10 signal EOM2. The input buffer enable lines
of input buffers 6U1A and 6U1B are connected together and driven by the
read input buffer (RIB) signal from CPU 414. In response to CPU 414
driving signal RIB low, input buffers 6U1A and 6U1B drive data lines D0
and D1.
Address input line A0 of both sound integrated circuits 6U6 and 6U10 is
connected to ground. Each sound integrated circuit, in this embodiment,
supports a maximum of 160 messages of 125 milliseconds each. Connecting
address input line A0 to ground halves the number of messages supported to
80, but the length of each message is doubled to 250 milliseconds.
Preferably, sound integrated circuits 6U6 and 6U10 have the
characteristics given in Table 1.
TABLE 1
______________________________________
Characteristics of Sound Integrated Circuits 6U6 and 6U10
______________________________________
1) Single-integrated circuit voice record and
playback
2) Direct Analog Storage Technology
3) Built-in microphone preamplifier, automatic
gain control, and filtering
4) Nonvolatile EEPROM technology
5) 5 VDC operation
6) 25 mA maximum current draw during operation
7) 10 .mu.A maximum current draw during power
down
______________________________________
An important aspect in selecting a sound integrated circuit is that sound
integrated circuits 6U6 and 6U10 require only a few external components so
that size, weight, and power consumption of portable data collection
terminal 300 is minimized. One sound integrated circuit suitable for use
in portable data collection terminal 300 of this invention is sold by
Information Storage Devices of San Jose, Calif. under Model No. ISD1020A.
FIG. 7 illustrates the flow of commands issued by decoder computer 401 to
voice prompt circuit 408 to record a voice prompt into sound integrated
circuits 6U6 and 6U10. To start the recording process at start step 701,
the user enters a number to identify the voice prompt to be recorded. Step
702, wait for key press, is then initiated. CPU 414 scans for signals from
keypad 302 and waits for the user to press a predetermined key to begin
recording.
When CPU 414 detects that the predetermined key for recording an oral
message has been pressed, load registers step 703 is initiated. CPU 414
loads the starting address of the message to be recorded into 8-bit
registers 6U4 and 6U5. The starting address is referenced to the number
entered by the user for the message. A timing diagram 800 of loading 8-bit
registers 6U4 and 6U5 with address AAH for sound integrated circuits 6U6
and 6U10 is presented in FIG. 8. The address on the CPU address bus is
represented by reference label A0-A15 and is simply shown as either 0005H
or 0006H. The remaining signals are the signals on lines CS5, CS6, -WR and
bus D0 to D7 (FIG. 6) respectively. FIG. 8 shows that first the signal on
line CS5 is driven low so that CPU 414 can write to register 6U5.
After the signal on line CS5 is taken low, the signal on line -WR is driven
low. When the signal on line -WR is low, the signals on lines D0 to D3, D5
and D7 are taken low and the signals on lines D4 and D6 are driven high.
When the signals on lines D0 to D7 are stable, the signal on line -WR is
driven high and the rising edge loads the values on lines D0 to D7 into
register 6U5.
After register 6U5 is loaded, the signals are dropped on line D0 to D7 and
the signal on line CS5 is taken high. This completes the loading of
register 6U5. Register 6U4 is loaded in a similar fashion when the address
0006H is driven on address bus A0-A15. Note that in loading register 6U4
with an address, bit D1 is driven low and bits D0 and D2 are driven high.
Note that in these examples unused data lines are driven low but either
state provides the same result.
After the registers are loaded with the starting address, in a first load
command step 704, CPU 414 loads the record command and the power-up
command into 8-bit register 6U4. CPU 414 beeps enunciator 308 in a first
prompt user step 705 to alert the user that the recording process is
beginning. This is immediately followed by CPU 414 loading the chip enable
command into 8-bit register 6U4 in a second load command step 706.
FIG. 9 is a timing diagram for loading 8-bit register 6U4 with the power-up
command followed by the chip enable command in record mode for sound
integrated circuit 6U6. Since bits 5 to 7 of register 6U4 control the chip
enable, power-up, and play/record respectively commands, CPU 414 writes to
I/O address 0006H. The timing sequence for signals on lines CS6, -WR and
data bus D0 to D7 is the same as that described for FIG. 8. First, the
signal on line CS6 is driven low. Next CPU 414 drives the signal on line
-WR low. After the signal on line -WR is low, CPU 414 drives the signals
on lines D0, D2, D6 and D7 high and the signals on lines D1, D3, D4 and D5
low. The signals on lines D0 to D7 are held in their respective states
until CPU 414 drives the signal on line -WR high which in turn loads the
record and power-up signals on lines D0 to D7 into register 6U4.
In start timer step 707, CPU 414 begins measuring the time of the
recording. The words spoken by the user into microphone 307 are recorded
by sound integrated circuit 6U6 or 6U10. Preferably, microphone 307 has
the characteristics given in Table 2.
TABLE 2
______________________________________
Characteristics of Microphone 307
______________________________________
Electret type
1K ohm impedance
Frequency response of 50-8K Hz
Sensitivity of 64 dB
Signal-to-noise ratio of greater than 40 dB
Less than 1 mA current drain
Operates on 2 to 10 VDC
______________________________________
One microphone 307 suitable for use in portable data collection terminal
300 is sold by Radio Shack of Fort Worth, Tex. under model number 33-1060.
Resistors 6R10 and 6R11 and capacitor 6C4 (FIG. 6) form a bias circuit that
provides filtered power to microphone 307. DC blocking capacitor 6C3 is
connected between microphone 307 and the preamplifier input stage of sound
integrated circuit 6U6. Capacitor 6C3 removes the DC component from the
low level audio frequency AC signal from microphone 307.
Inside sound integrated circuit 6U6, amplification is performed in two
stages. The audio frequency input signal from microphone 307 on pin MIC of
sound integrated circuit 6U6 is preamplified by an input preamplifier. The
preamplifier output signal is amplified by a fixed gain amplifier. The
fixed gain amplifier drives analog output pin AOUT. The signal path
between the analog output and analog input of sound integrated circuit 6U6
is completed by connecting a capacitor 6C2 between the analog output pin
AOUT and the analog in pin AIN of sound integrated circuit 6U6. Capacitor
6C2 provides an additional pole for low-frequency cut-off. The signal on
analog output pin AOUT of sound integrated circuit 6U6 can also be fed to
the slave sound integrated circuit 6U10 by connecting a capacitor 6C9
between pin AOUT of the master sound integrated circuit 6U6 and the pin
AIN of the slave sound integrated circuit 6U10. By making these
connections either integrated circuit may record the voice input from
microphone 307.
An automatic gain control (AGC) circuit inside sound integrated circuit 6U6
dynamically monitors the output signal level of the fixed gain amplifier
and sends a gain control voltage to the preamplifier. The preamplifier
gain is automatically adjusted to maintain an optimum signal level into
the input filter. This gives the highest level of recorded signal while
reducing clipping to a minimum.
The characteristics of the AGC circuit are set by two time constants; the
attack time and the release time. Attack time is the time required by the
AGC circuit to reduce gain in response to an increasing input signal.
Release time is the time constant of the gain increase in the presence of
a decreasing signal. Resistor 6R15 and capacitor 6C6 set the attack and
release time to optimum values for human speech. Noise-canceling common
mode rejection is provided in sound integrated circuit 6U6 to reduce
background noise from microphone 307 by connecting capacitor 6C7 between
pin MREF and ground. Capacitor 6C7 preferably has the same capacitance as
capacitor 6C3.
Following the fixed gain amplifier stage is an input filter. Although the
storage is analog in nature, sampling techniques are employed and
consequently require an anti-aliasing filter to remove or reduce input
frequency components above half the sampling frequency. With a sampling
frequency of 8 kHz, a high frequency cutoff for the low-pass filter of 3.4
kHz will satisfy the Nyquist Criterion and allow for a frequency band
width sufficient for good quality voice reproduction. The input filter is
a continuous time, 5 pole low-pass filter with a roll-off of 40 dB per
octave at 3.4 kHz.
With signal conditioning completed, the input waveform is written into an
analog storage array in the integrated sound circuit beginning at the
address stored in 8-bit registers 6U4 and 6U5. Samples are taken by an 8
kHz sample clock and each sample undergoes a level shifting process to
produce the voltage required for the nonvolatile writing procedure of the
EEPROM array. The sample clock is also used to increment the array decode
so that the input samples are stored sequentially in the array. All of
these processes are performed automatically by sound integrated circuits
6U6 and 6U10.
In time check 708, CPU 414 checks to see if the allocated time for the
message has expired. If so CPU 414, in a third load command step 709 loads
the disable and power-down command into 8-bit register 6U4. FIG. 10 is a
timing diagram of loading 8-bit register 6U4 with the disable and
power-down command for sound integrated circuit 6U6. The timing sequence
for FIG. 10 is similar to that described above for FIG. 8. Immediately
after loading the disable and power-down command CPU 414 beeps enunciator
308 in a second prompt user step 710 to alert the user that the recording
process has ended.
FIG. 11 illustrates the timing of the signals output from 8-bit registers
6U4 and 6U5 which drive input pins of sound integrated circuit 6U6. Time
t1 represents the initial state after power has been applied. | | |
