4-Way Intercom
4Way Intercom
Parts List
R1 10k
R2 150k
R3 4k7
R4 47k
R5 2k2
R6 4k7 trimpot
R7 390R
R8 10k
R9 100k
R10 100k
R11 22k
R12-R15 2k2
R16 4k7
R17 4k7
C1 0.22uF
C2 47uF
C3 1uF
C4 2,200uF (power filter cap รข€“ not shown, but wired across +12volts & 0v- ground points
Q1-Q5 BC547 n.p.n low gain
Q6 BC 549C high gain with a beta of at least 250+
D1-D7 1N4148 or 1N914 small signal diodes
IC1 NE 556 dual timer chip
IC2 CD 4017B decade counter chip
OC1-OC3 4N25 or 4N28 opto couplers
Tx 1k/8R transformer, with 1k centre tapped
B1-B4 9 volt DC buzzers mounted inside phone handsets
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