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# Multi-Position Mains Switch(78L09)

2015-09-14 10:42
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This paper introduces the Multi-Position Mains Switch (78L09). This principle is easy to understand, but also very practical. Depth understanding of circuit elements, you can better grasp this principle. In this circuit, you can learn about and purchase these components: 78L09.

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.

#### Figure 1

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 theCLKinput 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 ?rst time, Q0 will be high and Re1 will be energized.

#### Figure 2

When the mains switch is brie?y 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 theCLKinput, 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.

#### Figure 3

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 fromOKW, Bopla or Schyller. The 9V transformer is also fitted on thePCB.PCBscrew 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!

#### Figure 4

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

Capacitors:
C1 = 100nF
C2 = 10μF 63V
C5 = 2μF2 63V axial

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

Miscellaneous:
K1,K2,K3 = 2-wayPCB