Published in issue 305, December 2001
This article is mainly about the board and the uses to which it can be put. The circuit is simplicity itself and consists of four phono sockets, which can be individually switched to a fifth (common) socket. This fifth channel can be used as either an input or output. A big advantage of this type of passive switch is that the channels are electrically isolated from each other, as well as from the supply voltage for the relays. If this is not required, it is of course possible to connect all earths of the boards together.
R1,R4,R7,R10 = 1MOhm
R2,R5,R8,R11 = 3kOhm 9
R3,R6,R9,R12 = 1kOhm 2
C1 = 4µF7 63V radial
D1-D4 = 1N4148
T1-T4 = BC547B
JP1 = wire link (see text)
K1-K5 = cinch socket, PCB mount, e.g., Monacor/Monarch # T-709G
Re1-Re4 = mini relay, 2 c/o contacts, e.g., Conrad Electronics # 505170-24 (12V, 720Ohm )
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Please note. In view of the complexity of international markets, Elektor cannot guarantee the availability of components for this project.