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Simple Clap Operated Stairway Light Switch Circuit

Posted by merzaha gulhku Wednesday, April 10, 2013 0 comments
Stairways, corridors or small indoor passages often tend to be dark throughout the day irrespective of the outdoor ambient light conditions. Therefore keeping such passages illuminated all the the time becomes imperative, however this leads to unnecessary wastage of electricity.

 An innovative way of solving this problem has been discussed in this article, by employing a clap operated momentary light switch circuit.

The circuit diagram may be understood as follows:

The idea is to switch ON the connected lights in the corridor through a  clap sound, whenever the involved passage is utilized.
The clap sound triggers the circuit and keeps the connected lights switched ON for a few seconds or until the predetermined time is lapsed, after which the lights are automatically switched OFF.

The configuration is actually a transistor based clap switch, but without a flip flop stage, rather the flip flop is replaced by a delay OFF timer stage for the necessary switching and sustaining of the lights for a fixed predetermined period.
The stage as usual includes a sound sensor stage consisting of a mic and the subsequent transistor amplifier stage using a couple BC547 transistors.

The next stage consists of the PNP transistor BC557 which receives the signals amplified from the first stage via the 47uF capacitor.
The fed signals are further amplified to much greater levels for triggering the final LED driver stage.
The LED driver stage consists of a group of white LEDs which provides enough light for illuminating a small passage premise.
The two 39K resistors and the 220uF capacitors form the basic delay OFF timer and decides for how many seconds the driver stage remains ON with the LEDs lit.

The power to the circuit can be either applied by incorporating a standard transformer/bridge AC/DC adapter or if the circuit needs to be more compact, a transformerless power supply may be included with the below shown circuit.

All the NPN transistors are BC547B and the single PNP transistor is a BC557B, LEDs are ordinary 5mm high efficiency white LEDs.

The coil can be of any type, a 100mH choke will also do, its introduced in order to keep the circuit stable and for avoiding self oscillations.