Multi-Position Mains Switch


The circuit shown here
was born out of necessity after one of our colleagues had just renovated
his kitchen and realized afterwards that there were not enough
switches. Obviously he was not too keen to partially demolish the
kitchen to install a few additional wires in the already tiled wall.
That’s how the idea arose to develop a clever electronic circuit that
would operate two lamps with only one switch. All this appeared to be
easy to realize by adding a small circuit, consisting of a decade
counter, a diode network, two relays and a low voltage power supply.

The schematic shows how simple the design of the ‘multi-position‘
extension really is. K3 is connected to the switched wires that go to
the original light. K1 and K2 are the connections for the two new lamps.
The operation is simply based on the fact that at every low to high
transition at the CLK input of IC1 the active
output moves over by one position. In combination with the diode network
D4 through D7 this ensures that with a single wall switch it becomes
possible to control two outputs. When the mains voltage is applied to K3
for the first time, Q0 will be high and Re1 will be energized.

When the mains switch is briefly switched off and then on again it
will have no consequences for the 9-V power supply, because C4 is quite
large. But this will result in a trigger pulse on the CLK
input, so that Q1 will now be high and via D5 and D6 both relays are
energised. After another off/on cycle of the mains switch, Q2 will be
high, relay Re1 will de-energise and only Re2 is still activated. If we
repeat the off/on cycle once more we’re back at the starting position
and only Re1 is energized.

If the switch remains in the ‘off’ position then both relays will
also be off. A printed circuit board has been designed for this
extension so that the entire circuit will fit without any problems in a
waterproof enclosure from OKW, Bopla or Schyller. The 9V transformer is also fitted on the PCB. PCB
screw terminals can be used for K1, K2 and K3. Since the circuit is
directly connected to the mains voltage we emphasis that the well-known
safety rules need to be observed. When making any measurements or
performing other operations on the circuit is it absolutely necessary to
first break the connection to K3!

Resistors:
R1,R2 = 10kΩ
R3 = 33kΩ
R4 = 100kΩ
R5 = 10kΩ

Capacitors:
C1 = 100nF
C2 = 10µF 63V
C3 = 4µF7 63V radial
C4 = 470µF 16V radial
C5 = 2µF2 63V axial

Semiconductors:
D1-D7 = 1N4148
D8 = 1N4001
T2,T3 = BC547B
IC1 = 4017
IC2 = 78L09

Miscellaneous:
K1,K2,K3 = 2-way PCB
terminal block, lead pitch 7.5mm
T r1 = mains transformer 9V 1.5VA
B1 = B80C1500 (round case) (80V piv, 1.5A)
Re1, Re2 = 12V relay


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