This is a schematic for making a working Telephone Hold Button, with the added
benefit of digitizied music.  The cost is under $10.00 and all parts are very
easy to obtain at your local Radio Shack store.  The circuit is currently
being used all the time on my phone and it works flawlessly.  If you have any
questions or comments feel free to send them to me:
 
      Kevin J Ziese (Zarf!)
      1001B Signer Boulevard
      Honolulu, Hawaii  96818
      1-808-422-7381
 
 
 
Parts List

   - 1.2K Ohms resistor, 5% tolerance,
   - Tri-State LED
   - Audio Transformer 1K:8 Ohms
     Primary winding is 1K and the
     Secondary winding is 8 ohms, just
     like a headphone (8 Ohms).  The
     part costs $1.98
   - DPST Switch (Double Pole, Single
     Throw)
   - Some wire, soldering iron, etc
   - 9 volt battery (maybe)
   - A musical greeting card, any type


Construction Note.  If the voltage of the greeting card circuit is 1.5 volts
then you can skip the battery.  If the card uses 6 or more volts then you'll
need the 9 volt battery.  Schematic 1 is for >3 volt greeting cards, and the
2nd one is for 1.5-3 volt cards.


Schematic 1 ( >3 volt greeting cards)

        1.2K
 G -----++++---[  ]-----+
        R1      L1      +     (
                        +----)(--[----]
                        +    )(  [    ]
                        + T1 )(  [ U1 ]
                        +    )(  [    ]
           o            +----)(--[----]
          /             +     (   I  I
 R ------o   o----------+         I  I
                                  I  I
           o  S1                  I  I
          /                       I  I
         o   o--------------------I  I
         +                           I
         +---------------------[ 9 V ]


R1 - 1.2K Ohm Resistor $0.39
L1 - Tri-State LED $1.29
T1 - Audio Transformer $1.98
U1 - Greeting Card Circuit $3-5
S1 - DPST Switch $1.69
9V - Free at Radio Shcak w/Battery Card
G  - Green telephone wire, from wall
R  - Red telephone wire, from wall

Note:  The battery is needed because the phone line can't, easily, supply both
a 1.5 and 9 volt potential at the same point in time.



Schematic 2 ( 1.5-3 volt greeting cards)

                ----------------------
                I                    +
                I ----------------+  +
        1.2K    I I               +  +
 G -----++++---[   ]----+         +  +
        R1      L1      +     (   +  +
                        +----)(--[----]
                        +    )(  [    ]
                        + T1 )(  [ U1 ]
                        +    )(  [    ]
           o            +----)(--[----]
          /             +     (
 R ------o   o----------+



R1 - 1.2K Ohm Resistor $0.39
L1 - Tri-State LED $1.29 
T1 - Audio Transformer $1.98
U1 - Greeting Card Circuit $3-5
S1 - SPST Switch $1.69
9V - Free at Radio Shcak w/Battery Card
G  - Green telephone wire, from wall
R  - Red telephone wire, from wall


Note 1: If it doesn't work try reversing the red and green wires (polarity
will make a difference)  As a second caution keep in mind that the power
source for the greeting card must also be wired properly or it won't work.

Note 2: Remember, the battery isn't needed here because the device will get
its power from the phone line itself.  That's why the power lines are wired in
parrellel with the LED in this schematic.  It's also why we only need a SPST
switch, there's only one circuit to complete!