xvEPA
United States
Environmental Protection
Agency
Environmental Monitoring and Support EPA-600/4-78-026
Laboratory May 1978
Cincinnati OH 45268
Research and Development
Auto Answer
Circuit Design for
an Anderson
Jacobson AD 342
Modem
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL MONITORING series.
This series describes research conducted to develop new or improved methods
and instrumentation for the identification and quantification of environmental
pollutants at the lowest conceivably significant concentrations. It also includes
studies to determine the ambient concentrations of pollutants in the environment
and/or the variance of pollutants as a function of time or meteorological factors.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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May 1978
AUTO-ANSWER CIRCUIT DESIGN
FOR AN ANDERSON JACOBSON AD 342 MODEM
by
David C. Fleck
Physical and Chemical Methods Branch
Environmental Monitoring and Support Laboratory
Cincinnati, Ohio 45268
ENVIRONMENTAL MONITORING AND SUPPORT LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
This report has been reviewed by the Environmental Monitoring and Sup-
port Laboratory, U.S. Environmental Protection Agency, and approved for pub-
lication. Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
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FOREWORD
Environmental measurements are required to determine the quality of am-
bient waters and the character of waste effluents. The Environmental Moni-
toring and Support Laboratory-Cincinnati conducts research to:
6 Develop and evaluate techniques to measure the presence and
concentration of physical, chemical, and radiological pollu-
tants in water, wastewater, bottom sediments, and solid wastes.
o Investigate methods for the concentration, recovery, and
identification of viruses, bacteria, and other microbiological
organisms in water; and to determine the responses or aquatic
organisms to water quality.
o Develop and operate a computerized system for instrument auto-
mation; leading to improved data collection, analysis, and quality
control.
This report was developed by the Advanced Instrumentation Section of the
Environmental Monitoring and Support Laboratory, in the interest of distri-
bution of information to aid the advancement of laboratory techniques through
computerization.
Dwight G. Ballinger, Director
Environmental Monitoring § Support Laboratory
Cincinnati
111
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ABSTRACT
This report describes a circuit that connects a Western Electric Model
1001F Data Accessing Arrangement to an Anderson Jacobson Model AD 542 Modem.
It automatically answers the telephone and holds a data connection as long
as a received carrier is present. It self-resets upon loss of carrier, al-
lowing further incoming calls to be answered. It also disconnects and resets
if no carrier is received within ten seconds after answering. In addition,
the circuit allows for easy origination of calls to other systems.
This report is a result of work done in conjunction with the laboratory
automation project, sponsored by the Environmental Monitoring and Support
Laboratory of the Environmental Protection Agency. This work was accom-
plished over the period September, 1976 to June, 1977.
IV
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CONTENTS
Foreword iii
Abstract iv
1. Introduction 1
2. Design Objectives 2
3. Theory 3
4. Construction 5
5. Operation 6
6. Troubleshooting 7
Appendices
A. Parts List 8
B. Figures 10
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SECTION 1
INTRODUCTION
Manual telephone operation for data communication does not allow unat-
tended, dial-up, computer use. Not only is it necessary for someone to an-
swer the telephone and place it on an acoustical coupler, but it is also
necessary to hang up upon session completion to allow further incoming calls.
The circuitry discussed in this report was designed to eliminate the
need for human intervention in computer data communication by telephone. It
was also designed to allow easy origination of calls, so as to make full use
of a Modem.
In addition to the circuitry, necessary equipment consists of a Western
Electric Data Accessing Arrangement and a Modem capable of answer mode
operation.
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SECTION 2
DESIGN OBJECTIVES
The desired circuit functions were:
1. To answer a telephone equipped with a Western Electric Data
Accessing Arrangement (DAA), and connect a data path from the
DAA to a Modem.
2. To break the connection and reset the circuitry upon loss of
incoming carrier.
3. To break the connection and reset the circuitry if no carrier
is received within a given period after answering.
4. To provide an easy means to originate calls to other systems.
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SECTION 3
THEORY
Circuit operation can be divided into four areas, input, output, reset,
and control. The input circuitry provides conversion of the necessary con-
trol signals from Electronic Industries Association .(EIA) levels to (TTL) le-
vels. The output circuitry provides the TTL-to-EIA conversion, and also
drives front panel Light Emitting Diode (LED) indicators. The reset cir-
cuitry resets all sequential logic either on power-up or manually by push-
button. The control circuitry provides the necessary logic for the circuit
to accomplish the desired goals. A detailed block diagram is shown in Figure
1. Figure 2 is a schematic diagram of the logic circuitry, and Figures 3 and
4 show the power filtering and regulation and Integrated Circuit (1C) pin
connections.
Input circuitry is shown as blocks 1 through 4 on the block diagram.
These four blocks use two 9617, triple EIA receivers. These convert EIA RS-
232C logic levels. The RS-232C standard is such that +4 to +15 volts defines
a true logic level and -4 to -15 volts defines a false level. The 9617 1C is
also fail safe, that is, voltages between -4 and +4 (such as those for an
open or grounded line) are considered false. Also note that the output is in
negative logic. Two of the signals attached to these receivers come from the
DAA and two from the Modem. The signals from the DAA are:
1) SH, Switch Hook, that indicates the phone handset has been picked
up and,
2) RI, Ring Indicator, that indicates the phone is ringing.
The signals from the Modem are:
1) CD, Carrier Detect, that indicates a carrier is being received, and
2) DTR, Data Terminal Ready, that indicates the Modem power is one.
It is appropriate at this time to mention the two connections between
the DAA and the Modem that do not connect to the circuit. These are R, Re-
ceive, and T, Transmit, sometimes called Ring and Tip by telephone companies.
Output circuitry is represented by blocks 5 through 8. Blocks 5 and 6
consist of 9616, triple TTL to EIA drivers. These convert TTL to the RS-232C
levels needed by the DAA. These IC's also have negative logic inputs. Two
signals go to the DAA. These are:
1) OH, Off Hook, that signals the DAA to complete a DC circuit to the
phone company office in the same manner as when a phone is taken
off the hook, and
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2) DA, Data Available, that connects the audio signal from the phone
lines to the R and T terminals on the DAA.
Blocks 7 and 8 of the output circuitry consist of two sections of a 7404
hex inverter. These are used with a dropping resistor to drive front panel
LED indicators. These indicators show the DTR and CD signals from the Modem.
The signals are a quick indication of Modem status. DTR is a power-on indi-
cator, and CD shows when a connection is established to a user or system.
The reset circuitry provides power-up and manual reset functions. Block
14 produces a manual reset and consists of a pushbutton) with a pull-up resis-
tor, R5. Block 14 produces a power-up reset, and consists of an RC network,
made up of one-third of a 7410 triple 3-input NAND gate and one section of
the hex inverter. Note the use of negative logic here and throughout the con-
trol circuitry.
The control circuitry uses the TTL-level RI, SH, and CD signals and
through sequential and parellel logic produces an output signal (Pin6 IC6)
that causes both OH and DA. This signal should be present under these
conditions:
1) When the telephone receiver is lifted to originate a call (SH).
2) When a carrier is present, indicating a completed connection (CD).
3) When the telephone rings, to answer it (RI).
4) For a reasonable amount of time after the telephone rings, to allow
the person originating the call to respond with a carrier.
5) For a short time after the telephone is hung up in originating a
call, to hold the line until the Modem responds to the carrier.
The fourth conditions is met by stretching the third condition by ten
seconds. This takes place in block 11, and is accomplished by using half of
a 74122 dual monostable multivibrator. This is then logically OR'ed with the
first two conditions by block 12, another section of the 7410. Block 13 is
a circuit whose output is true whenever its input is true, and stays true for
approximately two seconds after its input goes false. This satisfies the
last condition and also allows for short dropouts in the carrier. The other
half of the 74122 provides the two-second dropout delay, and half of a 7474
dual D flip-flop and one section of the hex inverter are used for logic and
to remove the glitch that occurs when the two-second dropout delay is
initiated.
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SECTION 4
CONSTRUCTION
^
Construction may be wire-wrap, point-to-point, or printer circuit tech-
niques. Parts placement is not critical, but a placement that follows the
logic flow is an aid to troubleshooting. Figure 8 shows a suggested outline.
A printed circuit is desirable but wire wrapping is less time consuming when
making single units.
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SECTION 5
OPERATION
For the circuit to be used in the answer mode, the Modem must be capable
of answer operation and this mode must be selected. When the number asso-
ciated with the circuit is called, the circuit answers, (usually on the first
ring) and connects the Modem to the line, signified by an audible tone.
Within 10 seconds after the tone, the person originating the call must re-
spond with a carrier of their own. This is usually done by placing the tele-
phone receiver in a Modem coupler or by switching a terminal with a built-in
Modem to Data. Approximately one second after the answer Modem receives the
carrier, a data connection is established. Once established, the session may
proceed for as long as necessary. If there is a loss of carrier for more
than two seconds, the connection will be lost and must be reestablished by
the above procedure. All that is necessary to reset the circuitry at the end
of a session is to break the carrier, usually by hanging up the telephone.
To originate a call, the Modem must be in the originate mode. When a
call is made to another system, the other system responds with a carrier.
When this occurs, the telephone is hung up and, in approximately one second,
the carrier detect light should light. This indicates a connection is esta-
blished and may proceed for as long as necessary. Again, if the carrier is
lost for more than two seconds, the circuit will reset and the procedure will
have to be repeated to reestablish a connection. On most systems, a LOGOFF
or similar command is given to indicate the end of a terminal session and the
carrier is dropped shortly after receiving a LOGOFF command. If this is the
case, the circuit will self-reset after two seconds. If this is not the
case, it will be necessary to break the connection manually. This may be
done either by pressing the reset button or by picking up the telephone as if
to make another call. The carrier detect light will extinguish when the con-
nection has been broken.
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SECTION 6
TROUBLESHOOTING
Should any trouble with the circuitry arise, troubleshooting is fairly
easy. Probably the handiest tool for service is a logic probe. Caution
should be used for EIA-level signals because most probes will allow only a
positive input less than 7 volts and the high positive and negative voltages
present could easily damage the probe. As most signals are present long
enough to allow a reading, a Volt Ohm Meter (VOM) can be used for the EIA
measurements.
The synchrograms, Figures 5 through 7, can be used for determining what
logic levels should be present on most external and some important internal
points. The first item to check is the Modem power and circuit power.
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APPENDIX A
PARTS LIST
Cl 500 MF. (Part of Single Shot RC Network)
C2 1 MF. (Part of R4C2 Power Up Reset)
C3 100 MF. (Part of Single Shot RC Network)
C4 1 MF. (Power Supply Bypass)
C5 1 MF. (Power Supply Bypass)
C6 1 MF. (Power Supply Bypass)
Dl 12 Volt 1 Watt Zener (Power Supply Regulation)
D2 12 Volt 1 Watt Zener (Power Supply Regulation)
IC1 9617 (Fairchild EIA to TTL Converter)
IC2 9617 (Fairchild EIA to TTL Converter)
IC3 74122 (Dual Monostable Multivibrator)
IC4 7410 (Triple 3 input HAND Gate)
IC5 7404 (Hex Inverter)
IC6 7474 (Dual D Type Flip Flop)
IC7 9616 , (Fairchild TTL to EIA Converter)
Rl 39K Ohms (Part of Single Shot RC Network)
R2 470 Ohms (Current Limiter for LED)
R3 470 Ohms (Current Limiter for LED)
R4 120K Ohms (Part of R4C2 Power Up Reset)
R5 2.2K Ohms (Pull up Resistor)
R6 39K Ohms (Part of Single Shot RC Network)
8
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R7 47 Ohms (Current Limiter for Zener)
R8 47 Ohms (Current Limiter for Zener)
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14
Rl
(RING INDICATOR)
5H
(SWITCH HOOK)
CD
(CARRIER DETECT) I
16
1
1 C\/ Cl
TRANSLATOR
2
LEVEL I
TRANSLATOR]
3
LEVEL 3
TRANSLATOR
15
POWER UP
RESET
11
10 SECOND
> HOLD
^
^
k
p
t
^
j
r
12
-54OI
f\j__
^r
ho->-
4 •
1
|
r
13
2 SECOND
DROPOUT
DELAY
i
-O
i
*V
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11
IC3A
Rl 10 ' «. i n t 4 « ! '2
(RING INDICATOR! fe. • rtV>_ ,1s, . !: ISn 1 ' •- •— *• U * '
L.._ - ! 9
IC1B
2 2
SH 4 - ( "i ! ,
(SWITCH HOOK) ^ • •vwl ^ f £» i
a /i IC1C
T 1 "
CD --- 4- •• -.--.j
(CARBIFR nfTEO) > 9, ioall> V^>t. 5
i
ft IC2A
DTR , ,' ^ ! 5
(DATA TERMINAL fe » jv\.< t> t bo i
READY) ! J ' 3
IC5BV ^
_ _ *\ A
+5 4700
128K { R4 DATA /'
TERMINAL ^ 2
+' READY -±- J
i0f 4= C2 INDICATOR"
~ IC4B IC5D
+5 ^L^TN 5[>o6.
r^JESj
11 1
2
IC5A
R2
470Q
11
2 CARRIER
^ DETECT
r INDICATOR
IC4A
13
12
1
2.2KJR5 1S R6 C3
MANUAL , J |V^5l~lhll4 |C6
RESET 1 o ' « — i . . .
I 2—43
1 LJS O
± LT->-r{)c?R 2
1—^ -
5 Y IC5C
M
A 4]
DDE ,
ciKo-SrP1
VR 'sfcce
C7A
^»4
CLR J»
T, :=M>
l±j
* o !
P^l
i
i f ~r n
o OH
-> (OFF
HOOK)
~~^ DA
(DATA
AVAILABLE)
Figure 2. Circuit Schematic Diagram.
11
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POWER SUPPLY
CIRCUIT
+ 5
R7
+ 15
R8
15 » WV-
+12
47fl 12v
ZENER
-L- 1 uf
-12
Figure 3. Power Supply Regulation Circuitry.
i.e.
1
2
3
4
5
6
7
VOLTAGE
GND| +5
+ 12
-12
PIN NO.
7
7
8
7
7
7
7
14
14
16
14
14
14
—
—
—
—
—
—
—
14
—
—
—
—
—
—
8
Figure 4. I.C. Power Connection Table.
12
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LOGIC
LEVELS
1
1
9
RING INDICATOR
IC3A O OUTPUT
IC3B O OUTPUT
OFF HOOK AND DATA
CARRIER DETECT
AVAILABLE
1
0
SWITCH HOOK
APPROXIMATE TIME (SECONDS)
Figure 5. Answer Mode Synchrogram - Carrier Not Received.
13
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LOGIC
LEVELS
1
9
1
S
1
0
1
0
1
0
1
9
CARRIER 10
RECEIVED
APPROXIMATE TIME (SECONDS)
CARRIER
LOST
2 SECOND
DELAY
Figure 6. Answer Mode Synchrogram - Normal Operation.
14
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LOGIC
LEVELS
^
s
i
s
1
0
1
0
"
s
c
\
RING
INDICATOR
>
IC3A S OUTPUT
K
IC3B O OUTPUT
K
>J
X
OFF HOOK/AND
K
1
\
CARRIER DETECT
v N
\
SWITCH HOOK
/ N
/ ^
^
\
/
DATA
V X
A
\r
y|
v -
*
k
S
AVAILABLE [
1 1
\
\
*
V
4
(
>
[} \
/\>
,
i
t
\
)
PHONE
PICKED
UP
PHONE CARRIER^
HUNG RECEIVED
UP
CARRIER
2 SECOND DELAY LQST
2 SECOND
DELAY
Figure 7. Originate Synchrogram.
15
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500 MF
IC7
9616
s
4122 ^
7410
u
C3
100 MF
+
+ C,
7474
IC5
7404
00
9617
IC2
9617
Figure 8. Parts Layout.
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
REPORT NO.
EPA-600/4-78-026
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Auto Answer Circuit Design for an Anderson Jacobson
AD 342 Modem
5. REPORT DATE
May 1978 issuing date
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
David C. Fleck
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Environmental Monitoring and Support Lab.- Cincinnati, OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
10. PROGRAM ELEMENT NO.
1BD612
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Same as Above
13. TYPE OF REPORT AND PERIOD COVERED
In House
14. SPONSORING AGENCY CODE
EPA-600/06
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This report describes a circuit which connects a Western Electric Model 1001F
Data Accessing Arrangement to an Anderson Jacobson Model AD 342 Modem. It auto-
matically answers the phone and holds a data connection as long as a received carrier
is present. It self resets upon loss of carrier, allowing further incoming calls
to be answered. It also disconnects and resets if no carrier is received within
ten seconds after answering. In addition, the circuit allows for easy origination
of calls to other systems.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
COSATI Field/Group
Modems
Data Links
Automatic Answering
Computers
62A
62B
62D
3. DISTRIBUTION STATEMENT
Release to public.
19. SECURITY CLASS (ThisReport)
UNCLASSIFIED
. NO. OF PAGES
23
20. SECURITY CLASS (This page)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
•fr U.S. GOVERNMENT PRINTING OFFICE: 1978—757-140/1301
17
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