<><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><> < > < The United Phreaker's Incorporated Proudly Presents > < > < Music On Hold Adapter (Music Box) > < > < By: The Lost Avenger > < > < An Upi Production 1990 > < > <><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><> 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 SçD) 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 Ú-------------------------------¿ 697Hz | 1 2 3 A | | | 770Hz | 4 5 6 B | | | 852Hz | 7 8 9 C | | | 941Hz | * 0 # D | À-------------------------------Ù 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 æF Disc C3 - 0.1 æF Disc C4 - 470 æF 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. 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