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Line Switcher

A single phone for two lines

Published in issue 371, November 2007

Line Switcher

More and more ISPs, are offering subscribers an extra phone line using Voice over IP (VoIP) on top of their Internet access.

The project described here reduces this inconvenience by letting you connect a single phone to two lines at once, to avoid having to tie knots in the cables! It’s a phone line switcher that routes the ‘correct’ line to the phone automatically.

Resistors

R1,R2,R7,R8 = 33k

R3,R11,R18 = 10k

R4,R13,R27 = 1M

R5,R6 = 100

R9,R10 = 100k

R12 = 4MΩ7

R14,15 = 47k

R16,R17,R21,R22,R25,R26 = 1k

R19,R20 = 100k

R23,R24 = 470k

Capacitors

C1–C4 = 100nF (7.5mm pitch MKT)

C5 = 470 nF (7.5mm pitch MKT)

C6,C9 = 6μF8 100 V

C7,C8 = 10μF 100 V

C10,C11 = 220μF 10V non-polarised

C12,C13 = 10nF (5mm pitch Sibatit/ceramic)

C14,C15 = 100nF (5mm pitch Sibatit/ceramic)

Semiconductors

D1,D2 = BAT85

D3,D4 = 1N4148

D6,D7 = LED, 3mm, green (low power)*

D5,D8 = LED, 3mm, red (low power)*

T1,T2 = BC557

T3–T7 = BC547

IC1 = 40106BF

IC2 = 4093

IC3–IC7 = TLP620 (Toshiba optocoupler)

Miscellaneous

K1,K3,K4 = RJ11 6/4 phone socket (Hirose TM5RE1-64)

K2 = 2-way SIL pinheader for power: 9 V NiMH battery

S1,S2 = pushbuttons

RE1 = Bistable 5 V 2-pole c/o relay (Panasonic DS2E-ML2-DC5V or Omron G6AK-234P-ST-US)

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Magazine November 2007
UK371 (US $ 6.20)
 

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Please note. In view of the complexity of international markets, Elektor cannot guarantee the availability of components for this project.

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