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- The Conference Box - - By: Madd Max -
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What is a Conference Box?
After hooking a conference box on your line you can talk on two lines at
the same time. Therefore, if you already have 3-way on both lines, you could
talk to 4 people at the same time (5-Way...). This version works (Unlike that
box you can 'PICK UP' at Radio Shack...).
What do I need?
Item Description
---- -----------
C1 10-uF, 50-volt electrolytic capacitor
C2 Another 10-uF, 50,volt electrolytic capacitor
C3 10-uF, 15-volt tantalum capacitor
R1 10K, 1/4 watt, 10% composition resistor
R2 100-ohm, 1/4 watt, 10% composition resistor
Q1 2N3904 npn silicon transistor
S1 Dpst toggle switch
S2 Another Dpst toggle switch
T0 Telephone coupling transformer, Microtran T2110 or equivalent
Some wire or a circuit board (Design your own)
Some electronic equipment
A box
A little patience
Notes:
The 'Item' is used to indicate where it goes in the diagram. You can use
any transformer which is rated at about 900 ohms both primary and secondary,
over the frequency range of about 300 to 3000 Hz.
How does everything go together?
+ / C1 C2 / +
----,----* *------*------$-----@ @---------$----*----*----* *----------,-
Line 1 ' ! + @ @ + ! ! ' Line 2
' ! @ @ ! R1# '
' ! @ @ ! ! '
S1 ! @ @ \: ! S2
' Telephone @T0@ Q1 :--* '
' Set @ @ /: ! '
' ! @ @ ! !+ '
' ! @ @ R2# $C3 '
/ ! @ @ ! ! /
---------* *------*------------@ @--------------*----*---* *-------------
What did all that mean?
Symbol Meaning
------ -------
- Horizontal Wire
! Vertical Wire
* Point where wire splits, separates, merges, etc.
/
* *
'
'
' A Dpst toggle switch
'
'
/
* *
$ Capacitor
# Resistor
@ To the Transformer
+ Positive end (of line or capacitor)
- Negative end
\:
:-- Transistor
/:
How do I use it?
Pick up the telephone set and flip the first switch on. You should get a
dial tone. Dial someone and tell them to hang on. Flip the second switch and
you should get another dial tone. Dial another number. After they answer, you
should be able to talk to both of them and they should be able to talk to one
another. If you have 3-Way on one (or both lines) you can flip the switch
corresponding to that line on and off (RAPIDLY) to switch the 3-Way.
NOTE: Because you went to all the trouble of making this with a transformer, it
should sound PERFECT!