The Simplest Circuit

CD4013 based Staircase switch circuit

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If you really want to have classical staircase switch with push to switch on from one place and off from another place, here you have more circuits. Now you have two options to build the circuit here, one with light sensitive and another without it. Time delay is not incorporated here. We can use both facilities in a single IC or build them in separate ICs. Any or all of them can be used depending on the need.

Instead of ever present 555, this circuit now employs CD 4013 which has two D type latches in a single package. The circuit toggles a load with a momentary push button. Several push buttons can be fixed in parallel at various places to control the triac from any of those many locations. Two independent circuits can be made from a single IC. There are three options are here to show the flexibility of the idea and as a kind of tutorial for possible applications. Ideas from these circuits can be implemented in other similar circuits with due care.

A flip-flop is used to store or ‘lock’ one bit of information. This is known as ‘latching.’ Digital electronics and especially computers use a number of flip-flops, which latch several bits of data at the precise moment. There are a few variations of a classical flip flop i.e., JK, and RS. D type flip-flop is also one of them.

D-type flip-flop is just a clocked flip-flop with a single digital input D (D for Data). Every time a D-type flip-flop is clocked, its output follows whatever the state ofD is in. Intermediate state is avoided in this flip-flop. When the clock goes high, data at D (0 or 1) is transferred to Q. q will have the opposite of this state. When clock goes low, data remains unchanged. Q stores data until the clock goes high again when new data may be available.

CD4013 has two independent D type latches with set, reset, data and clock inputs. Both Q and are available as the outputs, which mean that both output states (high and low) or both toggle states are available. Set or reset is independent of clock.

TRUTH TABLE

No change

t = Level change Figure 30

x = Don’t care case

Now we have a series of circuits here using this IC. Circuit 1 and 2 are the same but the second circuit makes use of triacs. Third circuit has the option of light sensitivity incorporated in to it. Use of triac permits operation directly at mains. This IC has two D type latches and the description holds good for both. Hence it is possible to make two independent switches from the same IC.

The circuit is shown in Schematic As soon as the switch SI is pressed, clock input goes high and high data input is transferred to the output which drives a transistor, and hence forth a relay. Now q out put will be low and is coupled to data input now. At the next switch on of SI or S2, clock input goes high and data low. at D input is transferred to Qi transistor. Now Qj cannot any longer hold the relay up, and equipment switches off. Now Q Output is at high level, which is coupled to data input and the latch is ready for next sequence.

In general ICs do not like bad housekeeping, more so when handling mains voltages. Soldering is straightforward. A piece of Vero board is OK. CD4013 is a CMOS IC. Please respect it. Relays should be rated at the current required. Dl and D3 diodes are provided to protect the components from the back EMF generated by the relay coil. This is a standard method of relay circuit protection. Only two switches are shown as examples. You may add more number of switches for use at a number of different locations.

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