Audio/Video Switch

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.

Resistors:
R1,R4,R7,R10 = 1MOhm 
R2,R5,R8,R11 = 3kOhm 9
R3,R6,R9,R12 = 1kOhm 2
Capacitors:
C1 = 4µF7 63V radial
Semiconductors:
D1-D4 = 1N4148
T1-T4 = BC547B
Miscellaneous:
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 )