Various remote control based projects are already posted in www.bestengineeringprojects.com. Now here is unique remote control circuit called sound operated on off switch and it response only particular frequency of sound (4.5 KHz) and can control device from a distance of up to 4.6 meters (15 feet).
Most sound operated switch use clap sound or voice to activate the remote control. Tone frequency generated by clapping or voice control is not constant and designing of receiver circuit for a particular or ordinary clap or voice is very difficult. In order to overcome this problem we designed and verified a unique circuit called sound operated on-off switch. The unique about this circuit is, it works only on particular tone frequency.
Circuit Description of Sound Operated On-Off Switch:
As all remote control circuit utilizes two main section i.e. transmitter unit and receiver unit.
Transmitter unit: The block diagram of transmitter unit (sound generator) is shown in figure 1. It contains tone generator, speaker driver and speaker.
The heart of the circuit for transmitter unit is phase-locked loop (PLL) tone decoder (IC1). IC1 contains VCO (Voltage controlled oscillator) and is used to generate frequency of 4.5 KHz signal. The output tone frequency is given to the base of speaker driver transistor T1 which further drive the loudspeaker.
Receiver Circuit: Block diagram of receiver circuit is given in figure 3. This unit is \further divided into four sub unit i.e. tone amplifier, PLL tone decoder, flip-flop section and relay driver unit.
Tone amplifier: In the circuit sound operated On-Off switch microphone is used as sensor. Mic1 receives tone signal of 4.6 KHz from tone generation or transmitter circuit and converts it into electric signal. The output electric signal from microphone is very weak and need amplification, which is done by transistor T1 and T2. Transistors T1 and T2 is configured as two state, high gain AF pre-amplifier.