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TITLE PAGE
IBM PC Voice Mail Card
By
Daniel A. Durbin
Senior Project
ELECTRONIC AND ELECTRICAL ENGINEERING DEPARTMENT
California Polytechnic State University
San Luis Obispo, CA
1989
APPROVAL PAGE
Title: IBM PC Voice Mail Card
Author: Daniel Durbin
Date Submitted: March 15, 1989
Copyright (C) 1989 by Daniel Durbin
______________________ ________________________
Prof. Arthur Dickerson Signature
Senior Project Advisor
______________________ _________________________
Dr. James D. Harris Signature
i
TABLE OF CONTENTS
Section Page
ABSTRACT............................ iv
I. INTRODUCTION........................ 1
A. Purpose...................... 1
B. Problem...................... 1
C. Solution..................... 2
II. BACKGROUND.......................... 3
A. IBM PC Bus Interface......... 3
B. Telephone Line Interface..... 5
C. A/D and D/A Conversion....... 6
III. REQUIREMENTS........................ 7
IV. DESIGN.............................. 8
A. Address Decode............... 10
B. Data Bus..................... 13
C. Voice Digitizer.............. 15
D. Voice Reproduction........... 18
E. Audio Input Amplifier........ 18
F. Audio Output Amplifier....... 21
G. Telephone Interface.......... 22
H. DTMF Decoder/Ring Detector... 24
I. Software Program............. 27
V. DEVELOPMENT AND CONSTRUCTION........ 28
VI. TEST RESULTS........................ 29
A. ADC Test..................... 29
B. Audio End-around Test........ 30
C. DAC Test..................... 32
D. Telephone Interface.......... 32
E. Answering Mode Test.......... 32
F. Integrated test.............. 33
VII. CONCLUSION......................... 34
VIII. BIBLIOGRAPHY....................... 35
ii
APPENDICES
Section Page
A. Specifications....................... 35
B. Parts List and Costs................. 36
C. Wire List............................ 39
D. IC Location Diagram.................. 41
E. PC Board Layout...................... 42
F. Program Listing...................... 44
G. Hardware Configuration/Layout........ 49
TABLES
II-1 IBM PC Bus Pin-out................. 4
IV-1 Address Assignment................. 12
IV-2 Control/Status Register Bit Asgmnt. 15
V-1 Frequency Response Data............ 31
D-1 Wire List.......................... 39
FIGURES
IV-1 General Block Diagram.............. 9
IV-2 Address Decode Schematic Diagram... 11
IV-3 Data Bus Schematic Diagram......... 14
IV-4 Audio Input/Output Schematic Diagm. 19
IV-5 Telephone Interface Schematic Diagm 23
IV-6 DTMF Decoder Schematic Diagram..... 25
IV-7 Ring Detector Schematic Diagram.... 26
V-1 Frequency Response Plot............ 30
D-1 Wiring Diagram..................... 40
E-1 IC Location / PC Board Silkscreen.. 41
F-1 PC Board Layout - Component Side... 42
F-2 PC Board Layout - Solder Side...... 43
iii
ABSTRACT
The Voice Mail Card (VMC) functions as an
enhanced telephone answering machine and is
designed as a plug in card for the IBM PC and
compatibles. In addition to regular answering
machine functions, the VMC features programmable
outgoing message selection, response to caller's
touch tone signals, and remote programming
ability.
The function of the Voice Mail Card is to answer
incoming telephone calls, deliver outgoing
messages which are programmably selectable from
16 digitized audio messages which are stored on
the PC's hard disk, to record incoming messages
to the hard disk or optionally to an external
cassette tape recorder, to respond to a caller's
touch tone signals, and to enter a remote
programming mode as a result of a special code
sent by the caller.
Audio messages are processed digitally via A/D
and D/A converters which receive and send 8 bit
data to and from the IBM PC through a selectable
port address. A/D conversion is implemented
with the ADC0802 which is operated at a clock
rate of 512 Mhz.
iv
At this frequency, the conversion rate of the
ADC will be 8 khz yielding a bandwidth of 4 khz
which is the limit of the telephone line. This
same clock is used for D/A conversion which is
implemented with the DAC0830. 8 bit data is
read/written to/from the card via software and
stored on the hard disk or optionally to an
external cassette tape recorder.
Data is transferred to and from the card through
I/O port address 0278h which may be changed as
necessary by dip switch selection. A software
program controls data read and write operations.
A full featured pull-down windowing program is
provided which controls all features of the VMC
and operates in answer mode, program mode,
message record, and message playback modes.
A/D and D/A conversion, telephone line speech
interface, ring detection, and DTMF decoding are
performed by pre-packaged monolithic devices.
The entire circuitry resides on a 4-1/2" x 7"
printed circuit board which plugs into an
expansion slot in the IBM PC.
v
I. INTRODUCTION
A. Purpose
This project proposes an alternative to the
standard telephone answering machine and will
offer superior performance as a result of
versatile programmability through the use of the
IBM Personal Computer (IBM PC). The primary
purpose of this project is to provide the
designer with design experience interfacing to
the IBM PC, interfacing to the telephone line,
and digital-to-analog (D/A) and (A/D) analog-to-
digital conversion techniques.
B. Problem
To implement this design, a method of recording
outgoing messages (OGM), incoming messages
(ICM), detecting phone rings, and audio coupling
to the telephone line must be devised and
implemented.
C. Solution
Messages will be digitized using an A/D
converter and stored as 8 bit data on a hard
disk. The bandwidth of the telephone line, 4
khz, will be adopted for the bandwidth of
recorded messages. This requires a sample rate
of 8 khz (by the Nyquist criteria). Therefore,
the data rate will be 8 kbytes per second or 480
kbytes per minute. Since incoming messages can
be long and numerous, provision will be made for
optionally storing incoming messages to an
external cassette tape recorder. Audio will be
reproduced using a D/A converter and played back
to the telephone line and an external speaker.
The digitized data will be read/written by the
IBM PC through data buffers on the answering
card. Audio will be recorded from a microphone
and played back to a speaker. All circuitry to
implement this will reside on a 4-1/2" by 7" pc
board which will plug into an expansion slot in
the IBM PC.
Wherever possible, circuit functions on pre-
packaged monolithic devices are used to minimize
power consumption, pc board space, cost, and
scope of this project.
II. BACKGROUND
A. IBM PC Bus Interface
The type of IBM PC bus interface of interest in
this project is 8 bit parallel data read and
write operations. The simplest approach is to
use port addresses and the port read/write
instructions of the 8088 microprocessor. On the
IBM PC, port addresses are numbered from 0200h
to 03FFh of which some are assigned by IBM to
specific devices. Many of these addresses are
unassigned and are available for purposes such
as add-ons and expansion. The choice of address
to use then depends only on which addresses are
free in the particular system being considered.
The second parallel printer port is chosen as
the default port address, but for adaptability,
may be changed by the appropriate selection of
dip switch positions. The dip switch may be set
to select any of the port addresses allowed by
the IBM PC. With this configuration, 8 bit
parallel data I/O may be accomplished with
software's use of the 8088's IN and OUT
instructions. In TurboC, these instructions are
referenced with inportb() and outportb()
functions.
Port addresses are determined by decoding
address bits (A0 - A9, where bit A9 indicates a
port is being addressed). A port address on the
address bus is valid when address enable (AEN~)
is lowered. 8 bit data is then transferred using
the port read (IOR~) and port write (IOW~)
signals. The IBM PC bus signals are tabulated
below in Table II-1.
GND | B1 A1 | I/O CH CK~
RESET DRV | B2 A2 | D7
+5V DC | B3 A3 | D6
IRQ2 | B4 A4 | D5
-5V DC | B5 A5 | D4
DRQ2 | B6 A6 | D3
-12V DC | B7 A7 | D2
NOT USED | B8 A8 | D1
+12V DC | B9 A9 | D0
GND | B10 A10 | I/O CH RDY
MEMW | B11 A11 | AEN~
MEMW | B12 A12 | A19
IOW~ | B13 A13 | A18
IOR~ | B14 A14 | A17
DACK3~ | B15 A15 | A16
DRQ3 | B16 A16 | A15
DACK1~ | B17 A17 | A14
DRQ1 | B18 A18 | A13
DACK0~ | B19 A19 | A12
CLK | B20 A20 | A11
IRQ7 | B21 A21 | A10
IRQ6 | B22 A22 | A9
IRQ5 | B23 A23 | A8
IRQ4 | B24 A24 | A7
IRQ3 | B25 A25 | A6
DACK2~ | B26 A26 | A5
T/C | B27 A27 | A4
ALE | B28 A28 | A3
+5V DC | B29 A29 | A2
OSC | B30 A30 | A1
GND | B31 A31 | A0
-------------
Table II-1.
B. Telephone Line Interface
1. Speech
The telephone company equipment registers an
off-hook condition when a load which draws 20 ma
is placed across the two phone lines, TIP and
RING. The current is modulated and demodulated
to send and receive speech signals through the
lines. Factors involved in this process include
line impedance balancing, gain control, and
amplification. There are many manufacturers who
produce telephone speech circuits in monolithic
packages which perform these functions. To
simplify the design, a choice of one of these
circuits is made for the telephone speech
interface.
2. DTMF
Dual Tone Multi-Frequency (DTMF) tones are used
to represent Touch Tone digits. To decode these
tones, a series of band pass filters must be
used. Most practical are switched capacitor
filters. This method and frequency measuring
techniques are used by the M-957-01 DTMF
Receiver from Teltone. This is the chip used
for the purpose of DTMF decoding.
3. Ring
A ring signal consists of an 86 Vac signal which
is on for 2 seconds and off for 4 seconds. The
ring detector should present a high impedance to
the line. Inexpensive monolithic packages are
available to perform the function of ring detect
and provide a signal which may be conditioned to
deliver a TTL ring detect signal to the IBM PC.
C. Analog/Digital and Digital/Analog Conversion
National Semiconductor offers a wide variety of
ADC's and DAC's. The choice of which depends on
3 criteria: bit resolution, conversion rate and
interface. In this application, 8 bit data is
required at a conversion rate of 8 khz. The
data should be easily interfaced to a
microprocessor. The ADC0802 and DAC0830 satisfy
these requirements with flying colors.
III. REQUIREMENTS
In addition to the IBM PC Voice Mail Card, the
following equipment is necessary for full
operation:
* IBM PC XT or AT Compatible (10 Mhz max)
* MS DOS v3.0 or above
* 128k memory
* Hard disk (20 meg suggested)
* Telephone line
* External 8 Ohm speaker
* 600 Ohm dynamic microphone
* External tape recorder (optional)
The term "IBM Compatible" has been found to be
misleading. Some PC systems claim to be able to
run all software written for the IBM PC, but in
actuality don't. The Voice Mail Card was
designed to operate on an IBM PC XT and was
tested on an IBM AT 10 Mhz Compatible using MS
DOS 3.2.
The data hold time on the DAC determines the
maximum CPU clock frequency of 10 Mhz. The size
of the hard disk will determine the amount of
digitized data that can be stored. Voice
messages may be optionally saved in analog form
to an external tape drive which has a remote
start/stop control input.
IV. DESIGN
The VMC consists of the following components:
A. Address Decode
B. Control/Status Registers
C. Data Bus
D. Voice Digitizer
E. Voice Reproduction
F. Audio Input Amplifier
G. Audio Output Amplifier
H. Telephone Interface
I. DTMF Decoder / Ring Detector
J. Software Program
A general block diagram showing the inter-
connection of the above is shown in Figure IV-1.
Audio may be digitized from two sources - from
an external microphone, and from the telephone
line. When DATA READY is asserted, the ADC has
completed a conversion and the data will be
placed on the data lines when the address decode
circuit detects address 0278h on the address
lines. The CPU must read the data within the
sample period to avoid losing the next
conversion. Digitized audio may be written to
the DAC by placing 0278h on the address lines
and the desired data on the data lines. The CPU
should time writes with DATA READY (8 khz). The
DAC outputs to the AUDIO OUT amplifier which
drives an external speaker and the telephone
line.
A. Address Decode
The IBM PC system bus has 20 address lines (A0 -
A19) of which only the lower 10 are used to
decode I/O port or device addresses. The
signals may be interpreted as shown below.
| AEN A9 | A8 A7 A6 A5 A4 A3 | A2 A1 A0|
| port | port select | chip |
| Address | | select |
| Valid | | |
Valid port address range is from 0200h to 03FFh.
Some of these are used and others are not. The
best approach for address selection is a built
in dip switch allow to assignment different
addresses depending on the particular PC
configuration. The author choose the default to
be the second printer port (LPT2) addresses
0278h - 027Fh.
The address decode circuitry monitors the IBM PC
address lines (A0 - A9), address enable (AEN~)
and port read/write (IOR~ and IOW~) and produces
control signals which select operation of the
card. This method is shown shown in Figure IV-2
and is described in detail.
Address lines (A3 - A8) and address enable
(AEN~) are compared with the card address value
in S1 (whose default is 0278h) by an 8 bit
magnitude comparator which is enabled by the a
port I/O read (IOR~) or port I/O write (IOW~)
operation. This condition (XIOR + XIOW)~ is
decoded by discrete gates and applied to the
enable input of the comparator. The comparator
then produces card select (CS~) which is used to
enable two 1-of-8 decoders. The 1-of-8 decoders
further decode address bits (A2 - A0) and are
enabled by card I/O read and card I/O write
(XIOR~ and XIOW~). The outputs then become
register read (RA~ - RH~) and register write
(WA~ - WH~) control signals which enable the
various 3-state data registers on the card. The
assignment of the registers A - H is
tabulated in Table IV-1.
Address | Register | Read | Write
--------|---------------|---------------|-------
0278h | A | ADC | DAC
0279h | B | - | -
027Ah | C | - | -
027Bh | D | - | -
027Ch | E | - | -
027Dh | F | - | -
027Eh | G | DTMF | -
027Fh | H | STAT | CTRL
Table IV-1.
B. Data Bus
The Voice Mail Card data bus consists of 8 bit
data connected to the IBM PC data bus through a
three-state buffer which is enabled by card
select (CS~) and card I/O read (XIOR~). There
are five 3-state devices connected to the Voice
Mail Card data bus, the DAC, ADC, Status
Register, Control Register, and the DTMF
decoder. The status register monitors the state
of the ADC clock (DATA READY), DTMF signal
decode detect (DTMF), voice signal present
(VOICE), ring detect (RING), and phone off hook
(HOOK) signals. The control register holds
control signals for the tape drive and phone
hook relay.
The Data Bus Schematic diagram is shown in
Figure IV-3.
The status and control registers are assigned as
register H. From the view of the computer, the
status register is a read-only register and is
enabled by read register H (RH~). The control
register is a write-only register and is enabled
by write register H (WH~). These are data
registers which hold 8 bit card status and card
control signals whose assignment is tabulated
below in Table IV-2.
| Control Register | Status Register
--------|-------------------|------------------
BIT | Function | Function
--------|-------------------|------------------
MSB 7 | - | -
6 | - | -
5 | - | -
4 | - | -
3 | - | DTMF-Detect
2 | Mic-On | Voice-Detect
1 | Tape-On | Ring-Detect
LSB 0 | Off-Hook | Hook-Status
Table IV-2.
C. Voice Digitizer
The selection of an A/D converter is a
compromise between price and availability. The
ADC0802 was available and chosen. The ADC is
clocked at 512 khz which is set by RC
components. The conversion rate is then 512 khz
/ 64 clks/conversion = 8 khz. This will allow a
frequency response of up to 4 khz which will
cover the telephones bandwidth of 3.5 khz. The
ADC is shown in Figure IV-3.
The bandwidth of the telephone line is 3.5 khz.
For good results, the card will be designed for
a 4 khz bandwidth. According to Nyquist, a
sample rate of twice the highest frequency is
required to reproduce the original signal.
Therefore a sample rate of 8 khz is required.
The National Semiconductor ADC0802 digital to
analog converter is an 8 bit ADC with a maximum
conversion rate of 10 khz. It requires 64 clock
cycles per conversion. Therefore, for an 8 khz
conversion rate, a clock of 512 khz is required.
This is obtained with RC components connected to
the clock inputs of the ADC. The frequency can
be given by:
1
f = --------- Let R = 10 kohms,
1.1 RC
1
C = -------------- = 177.6 pF
1.1(10k)(512k)
The ADC is set to operate in the free running
mode by tying interrupt (INTR~) to write (WR~)
which has the effect of initiating another
conversion once the last conversion process is
completed. The ADC is therefore always
performing conversions. The (INTR~) output will
then be the clock frequency divided by the
conversion rate and thus will be 8 khz. The
state of the INTR~ output of the ADC is
monitored by a D FF which is cleared when a read
register A (RA~) or write register A (WA~)
operation occurs. The output of the D FF is
then a DATA READY signal which is monitored by
the status register for the CPU to examine. In
this manner, the CPU can time read and write
operations to the 8 khz clock on the card. The
ADC output data will appear on the card data bus
when read register A (RA~) is lowered which is
tied to read (RD~) on the ADC. This corresponds
to address 0278h appearing on the IBM PC bus.
The audio input should be a voltage from 0 to 5
Vdc and is produced by the Audio Input Amplifier
circuit.
D. Voice Reproduction
The DAC chip to be used is the DAC0830. The
hookup for this chip is straight forward. The
chip is double buffered but in this
configuration, this feature is not used. The
feedback resistor is used in a current-to-
voltage converter in the audio-out circuit. XFER
and WR2 are held low while WA~ is used as chip
select and XIOW~ clocks the data. Vref = +5
Vdc. The hold time of the data decreases as Vcc
increases. For a 10 Mhz CPU, Vcc should be +12
Vdc. +5 Vdc is sufficient for 6 Mhz operation.
The DAC is shown in Figure IV-3.
E. Audio Input Amplifier
The audio input amplifier consists of a high
gain inverting amplifier, low pass filter, level
shifter and activity detector. The sources of
audio input signals are from an opto-isolator
connected to the telephone interface circuit and
a microphone whose impedance is 600 ohms and
output signal is about 5 mV at a normal speaking
volume and a speaking distance of 3" from the
microphone. The input to the ADC0802 should be
from 0 to 5 Vdc centered at 2.5 Vdc. An
inverting amplifier is used to provide a gain of
5 V / 5 mV = 1000.
The audio signal should also be filtered to
contain minimum frequency components above 4
khz. A Sallen and Key two pole low pass filter
to provide low pass filtering. The gain and
poles are given by:
Av = 1 + R2/R1 f = 1 / 2 pi R C
The gain is set to slightly above one and the
poles to 4 khz by selecting R1 = 10 kohms and R2
= 27 kohms. Thus R2 = 12 kohms and C = 1500 pF.
The signal is then capacitively coupled to a
level shifter whose center is 2.5 Vdc and
limited by protection diodes to prevent values
greater than 5 Vdc and less than 0 Vdc.
A single-shot retriggerable multivibrator is
used as the activity detector and is set to 3
seconds by the timing components. The high time
is given by
tw = k Rext Cext, where k ~= 0.45.
Choosing the highest value of Rext yields Cext =
22 uF. The one-shot is connected to trigger on
the falling edge of the input signal. Since the
zero or "quiet" value of the audio out signal is
2.5V, the one-shot will trigger when the input
falls below 0.8V.
F. Audio Output Amplifier
The Audio Output Circuit is shown in Figure IV-4
and consists of a current-to-voltage converter
(since the output of the DAC is a current), a
Sallen and Key low pass filter, and an off-the-
shelf audio amplifier.
The digitized audio output of the DAC is
converted to a voltage by the DAC's internal 15
kohm resistor and the inverting OP-AMP U16. The
signal is then low pass filtered by a low pass
Sallen and Key filter whose high frequency is
set to 4 khz. This removes the discrete digital
steps produced by the DAC by smoothing them into
an audio signal.
The output of this low pass filter, along with a
sample of the audio input low pass filter, is
sent to an audio power amp (U17) through a gain
control (R32) which acts as a volume control.
The output of the power amp is then sent to an
external 8 ohm speaker and to an external
cassette tape recorder if available.
Samples of both the audio output and audio
inputs circuits are send to the Telephone
Interface circuit for coupling to the telephone
line.
G. Telephone Interface
The TCM-5700 monolithic speech circuit is used
to interface voice audio to the phone line.
Optosolators are used to isolate the IBM PC
power from the telephone line. The Telephone
Interface Schematic Diagram is shown in Figure
IV-5.
The phone line is taken off hook when the
software address the OFF HOOK bit in the control
register. The bridge rectifier BR1 converts the
telephone line's AC signal to DC for power and
use by the TP5700 speech circuit which is biased
and balanced with reference to its data sheet.
Since the telephone line must be isolated from
the IBM PC power and ground, opto-isolators are
used to couple the audio signals to and from the
audio circuits. Power from the TP5700 is used to
bias the receive LED and transmit transistor and
IBM PC +5 Vdc to bias the transmit LED and
receive transistor in the dual opto-isolator.
H. DTMF Decoder / Ring Detector
The DTMF decoder schematic is shown in Figure
IV-6 and the Ring Detector in Figure IV-7. The
DTMF decoder monitors the received audio from
the telephone interface circuit. When the DTMF
decoder detects a DTMF signal on the telephone
line, it will assert DTMF DETECT which may be
monitored by software by reading the status
register. If the computer responds by
addressing the DTMF decoder, the DTMF decoder
will place onto the data bus (XD0-XD3) a 4 bit
binary number equivalent to the touch tone
signal present on the audio line.
The ring detector is connected directly to the
phone line through a high impedance RC circuit.
Since the ring detector is powered by the
telephone line power, its output must be
isolated from the IBM PC. Opto-isolator U23
provides this isolation and produces RING which
is then sent to the status register.
I. Software Program
The software program used to operate the voice
mail card is written in TurboC v1.5 and controls
the reading and writing of digitized speech to
and from the card. It also monitors the voice
mail card status and takes appropriate action
such and picking up the phone in response to a
ring, and other control functions. The source
code for the program is many thousand of lines
long so will not be listed here, however, a
partial listing of of the program containing the
readADC() and writeDAC() functions is provided
as Appendix G.
The program (called ANSWER.EXE) is a window
driven program which provides interface to all
the features of the voice mail card. The user
may record outgoing messages, play back incoming
messages, manually dial a number, program the
out going message timer and anything else.
V. DEVELOPMENT AND CONSTRUCTION
The prototype for the VMC was built on a
prototype board during design and test. A
layout of the proposed circuit board is provided
in the appendices. The layout does not include
switching capacitors for the logic IC's which
should be added. Time did not permit
fabrication of the pc board, however, it is the
author's intent to construct the pc board
version of this project.
VI. TEST RESULTS
A. ADC Test
The first stage to be tested was the ADC. The
readADC() function was written to read and store
digitized audio from the ADC. A graphing
function was written to display the digitized
audio on the computer's monitor in high
resolution graphics mode.
B. Audio End-around Test
The audio input circuit was connected directly
to the audio output circuit and a frequency
response plot was made of the two circuits
combined. The combined circuits make up a four
pole band-pass filter with band of 100 hz to
4000 hz. The resultant frequency response data
is tabulated in Table V-1 and the corresponding
frequency plot is shown in Figure V-1.
R = 12k / (150k + 12k)
Hz | Vi x R| Vo | Vi | dB
-----|--------|-------|--------|------
70 | 52.31 | 0.22 | 3.875 | 35.0
100 | 52.40 | 0.40 | 3.881 | 40.3
200 | 52.42 | 0.65 | 3.883 | 44.5
400 | 52.03 | 0.82 | 3.854 | 47.0
700 | 51.86 | 0.91 | 3.841 | 47.5
1.5k | 51.68 | 1.05 | 3.828 | 48.8
1k | 51.74 | 0.96 | 3.833 | 48.0
2k | 51.72 | 1.20 | 3.831 | 49.9
3k | 52.42 | 1.20 | 3.883 | 49.8
3.5k | 52.78 | 0.99 | 3.910 | 48.1
4k | 52.84 | 0.78 | 3.910 | 46.0
5k | 52.51 | 0.41 | 3.890 | 40.5
6k | 52.28 | 0.20 | 3.873 | 34.3
7k | 52.21 | 0.10 | 3.867 | 28.3
Frequency response raw and calculated data
Table V-1.
C. DAC Test
The second stage to be tested was the DAC. The
writeDAC() function was written to send stored
digitized audio to the DAC. A speaker was
connected to the audio output circuit and the
resulting reproduction of audio was monitored
audibly.
D. Telephone Interface
The third stage to be tested was the Telephone
interface. A second phone line was used to dial
the phone to which the interface was connected.
The readADC() function was used to store the
digitized audio received from the phone line.
The writeDAC() was used to replay the digitized
audio.
E. Answering Mode Test
The fourth stage to be tested was the integrated
answering mode. For this test, the program was
used to monitor the ring signal and respond with
an OFF_HOOK command. An outgoing message was
then played to the caller. Once finished, the
incoming message was recorded until the VOICE
signal was no longer asserted. The resultant
recorded incoming message was played back
through the external speaker.
F. Integrated Test
The bulk of the user interface of the software
program was developed during this phase of
testing. The readADC() and writeDAC functions
were integrated into a pull-down windowing
program and support functions were written to
provide the programmability of the VMC.
VII. CONCLUSION
This project was successful. It was ahead of
schedule, under budget, exceeded specifications,
and performed outstandingly.
A. Bugs and Suggestions
The readADC() functions writes data to the hard
disk in 1 second blocks (4 kbytes) which takes
different amounts of disk access times with
different types of hard disks. With a 10 Mhz AT
and a 35 ms access time ST-251 hard disk, the
data write time takes more than the 1/4000th of
a second and results in data lost. A solution
would be to provide a data buffering RAM on the
card.
VII. BIBLIOGRAPHY
A. Interfacing to the IBM PC
by Lewis C. Eggebrecht. Howard W. Sams.
B. Introduction to Electronic Speech Synthesis
by Neil Sclater Blacksburg Howard W. Sams
C. Understanding Telephone Electronics
by John L. Fike. Howard W. Sams
REFERENCES
A. Motorola Schottky TTL Data Book
B. National Semiconductor Linear Databook
C. TelTone Corporation DTMF Receiver
M-957-01 Data Sheet
APPENDICES
Appendix A. Specifications
Conversion rate 8 Kbytes/sec
A/D Converter clock rate 512 Hz
Data Rate 480 Kbytes/minute
External Speaker
impedence 8 ohms
power 2 watts max
Microphone 600 ohms
Audio Gain 48 dB @ 1 Khz
Bandwidth 4 Khz
Phone line RJ-11
Appendix B. Parts List
Ref Des Description Part # Spec Tol U/I Price
BR1 Full-Wave Bridge Rectifier BR84D-ND 2a, 400v EA 0.77
C1 Capacitor, Electrolytic 2.2u 50V 20% EA 0.13
C2 Capacitor, Polypropylene 1500p 2% EA 0.39
C3 Capacitor, Polypropylene 1500p 2% EA 0.39
C4 Capacitor, Electrolytic 2.2u 50V 20% EA 0.13
C5 Capacitor, Polyprobylene 4700p 2% EA 0.39
C6 Capacitor, Polyprobylene 4700p 2% EA 0.39
C7 Capacitor, Electolytic 2.2u 50V 20% EA 0.13
C8 Capacitor, Mylar 0.047u 100V 10% EA 0.09
C9 Capacitor, Electrolytic 22u 20V 20% EA 0.13
C10 Capacitor, Metallized Polyester 0.01u 400V 10% EA 0.16
C11 Capacitor, Mylar 0.01u 100V 10% >10 0.09
C12 Capacitor, Mylar 0.047u 100V 10% >10 0.09
C13 Capacitor, Electrolytic, Radial 100u 16V 20% EA 0.45
C14 Capacitor, Mylar 0.22u 100V 20% >10 0.19
C15 Capacitor, Electrolytic, Tantalu 4.7u 50V 20% EA 0.14
C16 Capacitor, Mylar 0.1u 100V 20% >10 0.11
C17 Capacitor, Tantalum 10u 16V 20% EA 0.13
C18 Capacitor, Metallized Polyester 0.47u 250V 10% EA 0.36
C19 Capacitor, Electrolytic, Tantalu 10u 50V 20% EA 0.16
C20 Capacitor, Mica 180p 5% EA 0.15
C21 Capacitor, Electrolytic 470u 16V 20% EA 0.38
C22 Capacitor, Electrolytic 2.2u 50V 20% EA 0.13
C23-C33 Capacitor, Mylar 0.1u 100V 10% >10 0.11
D1 Switching Diode 1N4148 or eqLow I, Vf<.8v >10 0.05
D2 Switching Diode 1N4148 or eqLow I, Vf<.8v >10 0.05
Ref Des Description Part # Spec Tol U/I Price
J1, J2 Connector, Phone RJ-11 DIP EA 3.72
J3 Connector, Miniature SJ-441 1/8", 2 cond, EA 0.53
J4 Connector, Miniature SJ-441 1/8", 2 cond, EA 0.53
J5 Connector, Miniature SJ-441 1/8", 2 cond, EA 0.53
J6 Connector Subminiture SJ-M24 1/10 EA 0.39
Q1 Transistor, General Purpose Swit 2N3904 NPN EA 0.23
Ref Des Description Part # Spec Tol U/I Price
R1 Resistor, Carbon 560 1/4 WATT 5% 200 0.02
R2 Resistor, Carbon 560K 1/4 WATT 5% 200 0.02
R3 Resistor, Carbon 27K 1/4 WATT 5% 200 0.02
R4 Resistor, Carbon 27K 1/4 WATT 5% 200 0.02
R5 Resistor, Carbon 12K 1/4 WATT 5% 200 0.02
R6 Resistor, Carbon 10K 1/4 WATT 5% 200 0.02
R7 Resistor, Carbon 10K 1/4 WATT 5% 200 0.02
R8 Resistor, Carbon 10K 1/4 WATT 5% 200 0.02
R9 Resistor, Carbon 8.2K CF25 1/4 WATT 5% 200 0.02
R10 Resistor, Carbon 8.2K 1/4 WATT 5% 200 0.02
R11 Resistor, Carbon 12K 1/4 WATT 5% 200 0.02
R12 Resistor, Carbon 18K 1/4 WATT 5% 200 0.02
R13 Resistor, Carbon 10 1/4 WATT 5% 200 0.02
R14 Resistor, Carbon 220K 1/4 WATT 5% 200 0.02
R15 Resistor, Carbon 18K 1/4 WATT 5% 200 0.02
R16 Resistor, Carbon 10 1/4 WATT 5% 200 0.02
R17 Resistor, Carbon 620 1/4 WATT 5% 200 0.02
R18 Resistor, Carbon 1.5K 1/4 WATT 5% 200 0.02
R19 Resistor, Carbon 4.7K 1/4 WATT 5% 200 0.02
R20 Resistor, Carbon 56 RSF1A 1 WATT 5% 100 0.12
R21 Resistor, Carbon 1K 1/4 WATT 5% 200 0.02
R22 Resistor, Carbon 8.2K 1/4 WATT 5% 200 0.02
R23 Resistor, Carbon 5.6K 1/4 WATT 5% 200 0.02
R24 Resistor, Carbon 150 1/4 WATT 5% 200 0.02
R25 Resistor, Carbon 15K 1/4 WATT 5% 200 0.02
R26 Resistor, Carbon 820 1/4 WATT 5% 200 0.02
R27 Resistor, Carbon 2.2K 1/4 WATT 5% 200 0.02
R28 Resistor, Carbon 470 1/4 WATT 5% 200 0.02
R29 Resistor, Carbon 4.7K 1/4 WATT 5% 200 0.02
R30 Resistor, Carbon 1M 1/4 WATT 5% 200 0.02
R31 Resistor, Carbon 10K 1/4 WATT 5% 200 0.02
R32 Potentiometer, 15 turn 3006P 10K 10% EA 1.35
Ref Des Description Part # Spec Tol U/I Price
U1 Octal Bus Transceiver, Non-inver 74LS245 >10 0.69
U2 A/D Converter, uP compatible ADC0803LCN 1/2 LEA 4.95
U3 Octal Transparent Latch, 3-state 74LS373 >10 0.79
U4 Octal Transparent Latch, 3-state 74LS373 >10 0.79
U5 D/A Converter, uP compatible DAC0830LCN EA 4.75
U6 Quad 2-in NAND 74S00 EA 0.25
U7 Quad Buffer, Low enable, 3-state 74LS125A >10 0.39
U8 Dual D Flip-Flop 74LS74A >10 0.25
U9 8 Bit Magnitude Comparator 74LS688N EA 1.93
U10 8.2 Kohm Resistor Pack DIP 4116R-001-RC1/4 WATT 10% EA 0.59
U11 8 Switch DIP Switch 16 pin DIP >10 1.05
U12 1 of 8 Decoder 74LS138 >10 0.39
U13 1 of 8 Decoder 74LS138 >10 0.39
U14 DTMF Receiver M-957-01 Teltone dummy4.00
U15 Quad 2-in NAND 74S00 EA 0.25
U16 Wide Band Input JFET Op-Amp LF347N EA 1.49
U17 Low Voltage Audio Power Amplifie LM386N-1 EA 0.79
U18 DPST Relay PRMA2A05 5V EA 4.65
U19 Retriggerable Monostable Multivi 74LS123 >10 0.39
U20 Opto-Isolator, Dual MCT61GI If = 50% EA 2.50
U21 Telephone Speech Circuit TP5700AN Nat Semi dummy2.00
U22 Ring Detector TCM1520APTI dummy0.75
U23 Opto-Isolator H11A2 If = 20 EA 0.75
U24 Quad Bilateral Switch CD4016AE EA 0.29
X1 3.58 MHz Crystal Series CY3.57 AP18 >10 0.89
ZD1 Zener Diode 1N4746A 18V 100PR5% EA 0.25
------
$52.00
Appendix F. Program listing
-----------BEGIN ANSWER.H ------------
/*************************************************
* File: Answer.h
* Desc: Include file for the Answering card
* Date: 12/03/88
************************************************/
/* FILE ADCDAC.C: */
/* DOS interrupt vectors */
#define Keyboard 0x09 /* keyboard interrupt vector */
#define Timer 0x21
#define D8259 0x20
#define EOI 0x20
/* Answering card addresses and codes */
#define AnsDAC 0x0278 /* Digital to Analog conv address */
#define AnsADC 0x0278 /* Analog to Digital conv address */
#define AnsStatReg 0x027f /* Answering Card Status Register */
#define DataReady 0x01 /* Data Ready bit */
#define TouchTone 0x08 /* Strobe from DTMF decoder */
#define Audio 0x20 /* voice present */
#define NotRing 0x40 /* ring */
#define Clock 0x80 /* Clock bit */
#define AnsCtrlReg 0x027f /* Answering Card Control Register */
#define OffHook 0x01 /* Takes phone off hook */
#define OnHook 0x00 /* Places phone on hook */
#define Mute 0x02 /* Halves receive gain */
#define AnsDTMF 0x027e /* DTMF decoder */
#define DTMF 0xf0 /* */
#define Fclock 8000.0 /* 8 Khz conversion rate */
void interrupt keyboard_handler(void);
void read_adc(char *filename, unsigned char limit); /* limit in seconds */
char write_dac(char *filename);
void mask_timer(void);
void unmask_timer(void);
int read_dtmf(void);
-----------END ANSWER.H --------------
---------- BEGIN ADCDAC.C ------------
/*************************************************
* File: AdcDac.c
* Desc: Read and write drivers for the ADC and
* the DAC at address 0278
* Date: 12/03/88
************************************************/
#define MENU 1
#include <dos.h>
#include <stdlib.h>
#include <conio.h>
#include <string.h>
#include <io.h>
#include <stdio.h>
#include "answer.h"
#undef BUFSIZ /* increase the disk io buffer */
#define BUFSIZ 4096
void fopenerr(char *filename);
void interrupt (*old_keyboard)(void);
char _kbhit;
/*************************************************
* Function: Read_ADC()
* Desc: Reads bytes from the A/D conv at 0x0278h
************************************************/
void read_adc(char *filename, unsigned char limit)
{
FILE *stream;
unsigned long size, i;
char buf[BUFSIZ];
char ch;
size = (long)limit * 8000; /* 8,000 bps */
if (!(stream = fopen(filename, "wb"))) {
fopenerr(filename);
return;
}
setvbuf(stream,buf,_IOFBF,4096);
old_keyboard = getvect(Keyboard);
setvect(Keyboard, keyboard_handler);
delay(100);
if (kbhit())
getch();
_kbhit = 0;
i = 0;
mask_timer();
ch = inportb(AnsStatReg);
while ( !(ch & Audio) && !_kbhit)
ch = inportb(AnsStatReg);
while ( (ch & Audio) && !_kbhit) {
ch = inportb(AnsStatReg);
if (ch & Clock) {
fputc(inportb(AnsADC), stream);
if (i++ > size)
_kbhit++;
}
if (ch & TouchTone) {
read_dtmf();
_kbhit++;
}
}
fclose(stream);
unmask_timer();
setvect(Keyboard, old_keyboard);
if (kbhit())
getch();
return;
}
/*************************************************
* Function: Write_DAC()
* Desc: Writes bytes to the D/A converter 0x0278h
*************************************************/
char write_dac(char *filename)
{
char buf[BUFSIZ];
long j;
long size;
FILE *stream;
char dtmf;
char ch;
if (!(stream = fopen(filename, "rb"))) {
fopenerr(filename);
return(0);
}
setvbuf(stream,buf,_IOFBF,4096);
old_keyboard = getvect(Keyboard);
setvect(Keyboard, keyboard_handler);
delay(100);
if (kbhit())
getch();
size = filelength(fileno(stream));
j = 0;
_kbhit = 0;
dtmf = 0;
mask_timer();
while (!_kbhit && (j < size)) {
ch = inportb(AnsStatReg);
if (ch & Clock) {
outportb(AnsDAC, fgetc(stream));
j++;
}
if (ch & TouchTone) {
dtmf = read_dtmf();
_kbhit++;
}
}
fclose(stream);
unmask_timer();
setvect(Keyboard, old_keyboard);
if (kbhit())
getch();
return(dtmf);
}
/*-------------------*/
/* F O P E N E R R */
/*-------------------*/
#ifndef MENU
void fopenerr(char *filename)
{
printf("Cannot open %s\n", filename);
}
#endif
/*---------------------*/
/* R E A D _ D T M F */
/*---------------------*/
int read_dtmf(void)
{
char dtmf;
dtmf = 0;
if (kbhit()) getch();
while (!dtmf && !kbhit())
dtmf = (inportb(AnsDTMF) & DTMF) >> 4;
return(dtmf);
}
/*
* Check for keyboard press
*/
void interrupt keyboard_handler(void)
{
(*old_keyboard)();
_kbhit++;
}
/*
* Mask Timer
*/
void mask_timer(void)
{
outportb(Timer, inportb(Timer) | 0x01);
}
void unmask_timer(void)
{
outportb(Timer, inportb(Timer) & 0xfe);
outportb(D8259, EOI);
}
#undef BUFSIZ
#define BUFSIZ 512 /* set back to normal */
----------------- END OF ADCDAC.C -----------------
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