Clap Switch Views
Two of the PIC output pins are used to drive a bistable relay via transistors T2 and T3. This type of relay has two energising coils. A short electrical pulse on one of the coils is enough to switch the relay in one direction while a pulse to the other coil will cause the relay to switch back. This type of relay has two main advantages: the relay is latching in both open and close direction so a short pulse is all that is necessary to switch it. Secondly the latching feature ensures that the relay retains its switched state even during a power failure. Changeover relay contacts enable the unit to be wired together with a changeover type manual switch, allowing the equipment to be switched manually if for any reason the clap switch is switched off.
Pins 2 and 7 are used to switch a twocolour LED providing a visual indication of the switched state of the relay. The last output pin of the PIC is not used and is connected to a jumper to allow switching software options. Clapping relay Software When the signal level at GP1 goes low (clap detected) the program waits for approximately 200 ms during which time the LED glows red. After this period the LED switches to green and the software samples the input for approximately three seconds. If a second clap is detected during this period, the controller switches the output. After switching, the controller ignores any further clap sounds for approximately 10 s and the LED lights red. The output state is stored in EEPROM so that if a power failure occurs the software will switch the correct relay coil when power is re-established.
This is not a high fidelity audio amplifier. Its function is to produce no output for small sounds and large output for (slightly) bigger sounds, so the customary biasing network can be omitted. The 4.7 Megohm resistor in the previous version was as good as an open circuit, and its omission does not affect the operation of the clap switch in any way. Provided, of course, that you use that 10 microfarad electrolytic capacitor.
You have seen magicians doing this, a “clap” and the object vanishes. Obviously I am not here to teach you magic, however the present circuit is nothing less than a magical device, well certainly can be for the children. The proposed design of a clap switch circuit when integrated to any of your electrical appliance can be used to switch it ON and OFF simply through alternate clapping of your hand. The device becomes more interesting and useful because it does require any external mechanism or device to carry out the specified operations.
Clap Switch Images
