Controlling appliance by sound using counter (CD4017) and optocoupler

Activation and control of appliances through sound has always been fascinating. Imagine entering your room and switching on your lights/fan with sound of your flick. The circuit based project described here can be used to alternately switch on and off an electrical appliance. The idea is to take sonic input through a condenser mic and control the appliance at the output through a relay. The input is amplified for better sensitivity and supplied to a counter. This counter is configured to give alternate high and low pulses to the relay which in turn controls the device connected to it.

In this project, the condenser mic converts the sound signal sensed from the surroundings and converts them into the weak electrical signals and the transistor amplifying circuit amplifies the weak signals. Refer sound amplifier circuit for more details.

The circuit uses an optocoupler IC 4N350 to provide pulses to the counter IC 4017. An optocoupler is a 6 pin IC which contains a led, optically coupled to a phototransistor.

The 4017 is a decade counter IC. The output pin Q0 is connected to a red LED. Pin 2, which is the output Q1 is connected to relay as shown in the figure. The appliance is connected between the NC and common pins of the relay. The output Q3, pin 7 is connected to the reset pin 15 of the IC.

When power is switched on and there is no sound signal, the output of the amplifier is low and hence the optocoupler is in the off state. Since there is no pulse at pin 14, the default output pin 3 is in the high state, thereby glowing the red LED to indicate the off state of the appliance. Since pin 2, which is the output Q1 is low, the relay are energized as current flows from Vcc. As a result the common pin gets connected to the NO pin, there by switching off the electric appliance.

Whenever a small sound is produced by clapping or otherwise, the sound signals are converted into electrical pulses by the condenser mic. These pulses are amplified by the amplified unit. When the amplified signals are fed to the optocoupler the LED inside gets biased thereby turning on the phototransistor and producing a pulse. This pulse is used as a clock source for the IC 4017. As soon as the first pulse comes the output, Q1 becomes high and Q0 becomes low. The red LED glows off. The high output at pin 2, will de-energize the relay coil. The common pin of the relay will connect to the NC pin and the device will switch on.

Now when once again sound is produced, the second pulse will come to the counter IC, the output Q2, which is at pin 7 will become high. As pin seven is connected to the reset pin, the IC 4017 will come back to its original state and the output Q0 will become high. The red LED will glow and the device will be switched off.