Selective Hand Clap Response
This circuit’s design caters to the specific detection of two hand clap that occur in relatively rapid succession. It’s engineered to disregard single hand claps, continuous clapping, and most other sounds typically characterized by lower frequency content compared to a hand clap. While not infallible, the system proves suitable for straightforward household purposes like controlling lighting fixtures.
Circuit Overview and Operation
To comprehend the circuit’s fundamental functioning, we’ll briefly delve into the circuit diagram and the corresponding timing diagram.
Microphone Amplification and Signal Conditioning
The electret microphone captures sound, and its signal is initially amplified to an appropriate level for further processing. Two inverters from a 4049 IC, commonly known as a ‘hex inverter’ package, are utilized for amplification. By connecting high-value feedback resistors between the input and output of each inverter and coupling them with a capacitor (C3). A basic yet functional analog amplifier is formed. A specific value of capacitor C2 at the amplifier input ensures that only higher frequency sounds are amplified.
The amplified signal undergoes’squared’ processing before charging capacitor C4 via D1. The final two inverters, IC1e and IC1f, function as Schmitt trigger. The first inverter produces a negative pulse when the microphone picks up a sound of sufficient amplitude. The duration of this pulse depends on the sound’s length and the values of C4-R6, ensuring the output goes high only when the sound ends. The subsequent inverter generates a corresponding positive pulse.
Schmitt Trigger Operation and Load Control
The rising edge of the Schmitt trigger output signal is differentiated by C6-R9. Creating a positive-going pulse when the sound stops. This pulse triggers monostable IC2a, built around one half of a 4013 dual D flip-flop. If a second pulse occurs on D3 after the first one has ceased while the monostable’s output remains high, the clock input of toggle flip-flop IC2b goes high. This action causes the Q output to turn high, activating T1. Consequently, relay Re1 is energized, turning on the load, which will stay on until another valid clap command is received (toggle function).
Clap Recognition Indicator LED
LED D1 is linked to the Q output of IC2a and serves as an indicator for the time slot available for the two successive claps. It visually displays the circuit’s response to clapping inputs, making it clear when the system is ready for the next command.
Optimal Power Supply and Safety Considerations
For optimal performance, the circuit is ideally powered using a mains adaptor configured to provide around 12 V DC output voltage, considering a load of 40 mA along with the relay coil current. Selecting the appropriate power supply ensures stable and efficient operation of the circuit. When using the relay to switch mains-powered loads, strict electrical safety measures must be followed. This includes adhering to the relay contact ratings specified by the manufacturer and maintaining a minimum contact distance of 6 mm between all contacts and wires carrying the mains voltage. Safety precautions are crucial to prevent electrical hazards and ensure user safety.
Relay Considerations for Circuit Reliability
The relay’s coil resistance should not fall below approximately 400 Ω to prevent overloading of T1 and ensure the supply voltage remains stable when the relay activates. By maintaining an appropriate coil resistance, the relay operates within safe parameters, preventing potential damage to the components and maintaining the circuit’s reliability. Additionally, only the make contact of the relay is utilized, ensuring efficient and controlled switching of the connected loads.