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< Music On Hold Adapter (Music Box) >
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< By: The Lost Avenger >
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< An Upi Production 1990 >
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Reprinted In File Form On March 4, 1990
Orignally Publised In Radio Electronics August 1989
===============================================================================
Music On Hold Adapter
By Steve Sokolowski
Have you ever been in the middle of a phone conversation, and need to
either walk away for a couple of minutes or switch lines? The kids might be
crying, the washing machine might need fabric softener, whatever. Here's an
inexpensive "Electronic hold button" controlled by a Touch Tone phone, with
provision for audio for the other party, using either a music synthesizer IC
module or a radio.
Unlike normal hold buttons, this one doesn't cut your phone handset off
from the other party; you can still hear one another, ans also the audio, if
you use it. Rather, what it does is let you provide this audio to the other
parrty, and then lets you hang up the handset without losing your party; you
can also opt for silence. When you wish to resume conversation, pressing the
pound (#) key shuts off the audio if used, and allows you to hang up and
disconnect when you need to know how hold buttons and Touch Tone phones work.
Placing A Call On Hold
The normal on hook voltage of a phone line is about 50 volts, depending
on particular central office equipment. When you lift a phone's handset, 600
ohms is place acriss the phone line, dropping the voltage to 5 volts.
The hold adapter prevents a disconnection when you hang up the handset,
by placing R6 And LED1 across the phone line using RY1. The synthesizer
provides music for the party on hold; it can be left out if desired.
Touch Tone Operation
Touch Tone Phones produce Dual Tone Multi Frequency (DTMF) signals,
using a 4 X 4 keypad that produces two tocuh tone sinusoidal outputs. The
frequencies are determined by the key row and column (see Figure 1); The row
frequencies are lower than those of the columns, and a Touch Tone signal is the
sum of both. Normal Touch Tone pads have 12 keys, but the operator console
keys (A-D) which normally aren't used.
Adding two sinusoids is equivalent to multiplying two sinusoids whose
frequencies are the difference if the orginals. Early Touch Tone pads used
indicators and capacitors; modern versions are crystal controlled intergrated
circuits that create staircase sinusoids.
Circuit Description
The G8870 represents each tone pair as a 4 bit code, where the column
of a key is the first two bits, and the row of a key is the second two bits;
both pairs of bits range from 00-11. This 4 bit code is then decoded by a 4514
4 to 16 decoder (IC3) to give the digit dialed.
Pressing the (*) key on a Touch tone phone adds a 1209Hz sinusoid (a
Row 4 tone), and a 941 Hz sinusoid (a Column 1 tone), to give a binary code of
1100. Similary, pressing (#) key adds 941Hz And 1477Hz sinusoids, to give a
binary code of 1100.
If a user preses a key on a Touch Tone phone used to operate the hold
adapter, pin 15 (Strobe S?D) Of IC1 goes high. That stobe output is inverted
by NOR gate IC2-a, and is fed to pin 23 (INHIBIT) OF IC3, enabling that device.
If The Touch Tone key pressed is either (*) or (#), then either pin 19 or pin
14 of IC3 goes high, since those are the pins corresponding to these keys. Pin
19 of IC3 goes to pin 12 of IC2-b, and pin 14 of IC3 goes to pin 5 of IC2-c.
Note that IC2-b and IC2-c are used to create a NOR gate reset set (RS)
flip-flop, which then controls RY1.
Since only one Touch Tone Key is interpreted at a time, there's no
mormal instance when both pin 19 and pin 14 of IC3 fo high simultaneously; that
only happens when IC3 is deferctive or there's a short. If neither the (*) key
nor the (#) key have been pressed, then both pins stay low. Pressing the (*)
key drives pin 12 Of IC2-b high and pin 11 of IC2-c goes low. Similarly
pressing the (#) key drives pin 5 of IC2-b high and pin 4 of IC-b goes low.
When pin 4 Of IC2-b, goes high by pressing the (*) key, Q1 turns on and
the contact of RY1 closes, preventing a disconnection when you hang up the
handset. That's because phone line current now flows through R6, the secondary
of T2, and the hold indicator LED1, which is now lit. When pin 4 of IC2-b goes
low by pressing the (#) key, Q1 turns off, current stops flowing through the
coil of RY1 (opening its contact), and disconnecting the hold adapter. The
hold adapter doesn't work as a standard hold button, because pressing the (*)
key doesn't disengage your phone handset. It just lets you hang up or switch
to another lone without being disconnected, because a second current path is
now across the phone line.
To include audio, the music synthesizer module goes in parallel with
LED1, and the audio fed from the synthesizer to the primary of T@. The audio
modulates the 5 volt phone line voltage and is heard by both you and the party
on hold. If you prefer either dialogue or some other music, you can replace
the synthesizer with a radio that has an earphone jack.
To do that, plug an external earphone cord into the jack, and connect
an earphone jack to the PC board hole for the synthesizer output, using S2 (an
SP3t switch) as indicated. For silence, jumper the secondary of T@; that can
be done using either a jumper or S2, although the use of S2 is strictly
optional. Just remember that pressing the (*) key lets you hang up without
being disconnected, but doesn't disengage the handset. The hold adapter uses
IC4, a 7805 5 volt DC regulator with C4 as filter, and 12 volt DC, 250mA, wall
transformer T1; S1 is used as the ON/OFF switch.
Construction
User sockets for the IC's, transistor (if desired), and relay. Any
suitable cabinet will do, and user a 1 amp, 120 volt to 12 volt DC wall
transformer. Use screws and spacers or adhesive foam to attach the PC board to
the cabinet. You can use any SP3T switch you want for S2, as long as it'll fir
in the cabinet.
Music synthesizer modules play repeating 30 battery socket and speaker.
The 1.5 volt battery socket and speaker. The 1.5 volt battery will likely be
present; the speaker may be, depending on the model. Note the polarity of the
battery (if present) before removing it.
The mechnical ON/OFF switch depicted is a metal flap, riveted on the
the right end, and with the left end on the right end, and with the left end
resting against the module board by spring tension. Connect the pad on the PC
board labeled "1.5 V" to the synthesizer's battery terminals, break the speaker
wires or foils (if the speaker is present), and the solder any ON/OFF switch
closed. Attach the synthesizer to the PC board using doublesided tape or
adheasive foam.
The two PC board pads underneath the "1.5V" label connect the audio to
the primary of T2. The secondary of T2 goes in series with R6 and LED1, adding
audio to the 5 volt DC offhook voltage. For silence, jumper the secondary of
T2. To display all 10 decoded Touch Tone keys, install R9 to R18 And LED2 to
LED11 (with bezels), the former mounted in the PC board, the lattered mounted
on the the front panel of a cabinet.
Installation And Test
Connect the red and green wires of a standard phone cord to their PC
board locations; the yellow and black wires aren't used. The other end plugs
into a T adapter with two RJ-11 female telephone sockets feeding into one RJ-11
male telephone plug. Plug the hold adapter and the Touch Tone phone into the T
adapter, and plug the T adapter into the telephone jack.
To test the hold adapter, dial a friend; if R9 to R18 and LED2 to LED
11 were used, the LEd corresponding to the Touch Tone key pressed should light.
To place a call on hold, press the (*) key; RY1 will close, connecting R6 and
LED1, audio should now be heard by you in the handset if the synthesizer or a
radio is present, and you can now hang up the handset. Pressing the (#) key
disengages the hold adapter, opening RY1's contact, disconnecting R6 and LED1,
and stopping the audio. Since the current path had now been removed, hanging
up the telephone will disconnect your party, unless you first press the (*) key
again.
Figure 1:
Touch Tone Keypad
1209Hz 1366Hz 1477Hz 1633Hz
?-------------------------------?
697Hz | 1 2 3 A |
| |
770Hz | 4 5 6 B |
| |
852Hz | 7 8 9 C |
| |
941Hz | * 0 # D |
?-------------------------------?
Schematics To Music Box:
Parts Needed
-=-=-=-=-=-=
Resistors
=-=-=-=-=
R1, R2, R4 - 100,000 Ohms, 1/4 Watt, 5%
R3 - 47,000 Ohms, 1/4 Watt, 5%
R5 - 50,000 Ohms, 1/4 Watt, 5%
R6 - 120 Ohms, 1 Watt, 5%
R7 - 220,000 Ohms, 1/4 Watt, 5%
R8 - 1,000 Ohms, 1/4 Watt, 5%
R9 To R18 - 1,000 Ohms, 1/4 Watt, 5%
Capacitors
=-=-=-=-=-
C1, C2 - 0.01 ?F Disc
C3 - 0.1 ?F Disc
C4 - 470 ?F 16 Volt Axial Tantalum Electrolytic
Semiconductors
=-=-=-=-=-=-=-
Q1 - 2N222 Transistor
IC1 - California Micro Devices G8870 Touch Tone Reciever
IC2 - 4001 Quad NOR Gate
IC3 - 4514 1 of 16 Decoder (High Output)
IC4 - 7805 5 Volt DC Regulator To 220 Type
LED1 To LED11 - Standard Red LED's
Other Components
=-=-=-=-=-=-=-=-
S1 - SPST 120 Volt AC Switch
S2 - SP3T Rotary Or Slide Switch
T1 - 120 Volt AC To 12 Volt Dc, 250 mA, DC Wall Transformer
T2 - Audio Transformer, 1000 Ohms Primary, 8 Ohms Secondary (Mouser
Electronics, Catalog NUmber 42tm013)
RY1 - 6 Volt SPST Relay With 100 Ohm Coil
XTAL1 - 3.58 MHz Crystal
MODULE1 - Music Synthesizer Module
Miscellaneous
=-=-=-=-=-=-=
Suitable Cabinet
4 Wire Phone Cord With Open Wires On One End Or Spade Lugs
4 Prong Or RJ-11 Modular Male Plug On The Opposite End
Dual RJ-11 Socket To Single RJ-11 Plug T Adapter
Female To Female Rj-11 Adapter
Solder
Wire
NOTE: A kit of parts is available from De-Phone Industries, PO Box 5835,
Spring Hill, Florida 34606. The kit includes the single sided PC board
($7.50 US), G8870 Touch Tone Receiver IC ($10.00US), T Adapter
($2.20US), 3.58 Mhz Crystal ($1.75US), And Music Synthesizer Module
($1.75US); Send $15.70US for all parts. Allow 3-4 weeks for delivery,
and include $2.50Us for shipping/handling. Florida residents include
sales tax; Canadian residents send money order in US funds, with $3.25
shipping/handling. No personal checks, please.
?------------------------------------------?
|?-----------------------------------------??
?---o Green || 1?-------? ||
| || ?-? Ic2-a |3 ||
| ?-o Red +5V || ?----------------o | 4001 0----------? ||
| | ?----------? || | ?-? | | ||
| o-C1-R1-o-----|1 IC1 18|-o || | +5V 2?-------? +5V?| ||
| | | | | C3 || | ?-------------------------------?|| ||
o-?-C2-R2-?-o---|2 17|-o || | ?|1 Strobe Ic3 24|?| ||
| | | o---|3 | R7 || | | Data1 4514 Inhibit 23|-? ||
| | R3 R4 | 16|-o ||??---|2------? ?-----------? | ||
| | ?-?---|4 15|----???? | ?-| Latch 1 |--?Data4 | ||
| | ?-o---|5 14|----?|| | Data2?-| |-??----22|---?|
| | | ?---|6 13|-----?| ?--|3------? ?-?--?--?--?? | | |
| | Ground | 12|------? | | |A |B |C |D |Data3 | |
| | ?---|7 11|--------??-|4-(7)----?-?--?--?--?? ?-----21|----?
| | Xtal | | ?---?-|5-(6)----| |---(0)-20|----?
| | ?---|8 10|? ??---?-|6-(5)----| 4 To 16 |---(*)-19|-? |
| | ?---|9 || ???---?-|7 (4)----| Decoder |---(8)-18|-?? |
| | Ground?----------?| ????---?-|8-(3)----| |---(9)-17|-???|
| | +5V-??????---?-|9-(1)----| |-------16| ||||
| | o-----??-----? ??????---?-|10-(2)---| |-------15| ||||
| | 4| || |11 ||||||?--? | | |---(#)-14|?||||
| | ?--0--? || ?--0--? ||||||| |11-------| |-------13||||||
| | |Ic2-c| || |Ic2-b| ||||||| ?-|12-------?-----------? ||||||
| | |4001 | || |4001 | ||||||| | ?-------------------------------?|||||
| | ??---?? || ??---?? ?-?||||||Ground ?-------------?||||
| | |5 |6 || 13| 12| |?-?||||?-------------------? |?-------------?|||
| | | ?---?? | | ||?-?||?---------------? | || |||
| | | ?----? | |||?-??-----------? | | || ?-----------?||
| | | ?---????--------------?----?----?---?? | ?-------?|
| | | |||?---------? | | | | | | |
| | | ||?-----? | | | | | | | ?--?
| | | ?-??-? | | | | | | | | |
| | | R9 R10 R11 R12 R13 R14 R15 | R16 R17 R18
| | | |(1) |(2) |(3) |(4) |(5) |(6) |(7)| |(8) |(9) |(10)
| | | Led2 Led3 Led4 Led5 Led6 Led7 Led8 | Led9 Led10 Led11
| | | | | | | | | | | | | |
| | | ?----o----o----o----o----o----? | ?----o-----?
| | | Ground | Ground
| | ?----------------------------------------------------?
| ?----------------?
?--------? |
?-----? | |
| RY1 0 | |
| 0-?? ?----------------------------?
| 0-?------? |
?-----? | +15V| |
?--?--? | |
?---| RY1 || | |
| | Coil|? | |
| ?-----? | |
| ?Ground | |
| | | ?---------?| ?-----------?
??---?? R6 ?---| Radio || o----| 120 Vac |----?
| Q1 | | 0 Slience |?--| || | | to 12 Vdc | |
| | A| S2 0 Radio---?| ?---------?| | | 25mA | |
?--?--? ?----o ?0----0 Music | ?---------?| 120 Vac | Wall | |
| | | | ?---------?--|Module 1 || | |Transformer| |
| | Sec T2 Pri ?---------o--| || o----| T1 |-? |
| | | | | ?-?------??| ?-----------? | |
| ?----o ?-----? |- +| | Out?-----?In | |
| B| | 1.5V | | ?---o--| Ic4 |--0--0--? |
| | | | | | | | 7805| 0 S1 |
| ?-Led1-o-----------------------? | | | +| | | |
| ?-------------------------------------? | | C4 ?--?--? |
?--------------------------------------------? | | |Gnd |
| | | |
| ?-----o--------------?
0 Ground
5 Volts
You may distrubute this file freely but may not change any part of this file in
whole or part without the written or verbal concent of the author.
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Call These Great Upi Boards!
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===============================================================================
03-06-90/006 Copywrite 1990 By The Lost Avenger-All Rights Reserved
Downloaded From P-80 International Information Systems 304-744-2253 12yrs+