Wireless control of device using infrared is not new to electronics hobbyist. Now, here is a wireless control of device using ultrasonic sound wave tested in BEP Lab. The project ultrasonic Lamp-brightness controller uses ultrasonic sound wave (above 20 KHz) for remote control of lamp brightness.
As all wireless control system Ultrasonic lamp-brightness controller basically comprise a transmitter and receiver circuit.
The transmitter circuit generate ultrasonic sound wave of about 40-50 KHz frequency using ultrasonic transducer and transmitter circuit. The receiver senses the transmitted frequency from transmitter circuit, amplify it and control brightness of lamp using corresponding circuit. The block diagram of ultrasonic lamp brightness control is shown in figure 1.
The transmitter section consist, a decade counter CD4017 (IC1), which is configured as free running astable multivibrator. The frequency of 40-50 KHz is generated by transmitter circuit and is converted into ultrasonic sound wave of same frequencies by ultrasonic transducer. The variable resistor VR1 is used for setting the transmitted frequency to 40 KHz.
The receiver circuit of ultrasonic lamp brightness controller is so designed that it receives transmitted ultrasonic sound wave. As in transmitted circuit, receiver circuit also used ultrasonic transducer called receiver ultrasonic transducer. The frequency received by receiver is converted into electrical signal of same frequencies.
Transistor T1 and T2 is used to amplify the signal up to appropriate level. The amplified signal is further rectified and filtered by using diodes D1 & D2 and capacitor C6 respectively. The filtered DC output is obtained, and is given to pin 2 (inverting pin) of operational amplifier IC2. The variable DC voltage is given to pin 3 (non-inverting pin) through variable resistor VR2. If determines the threshold value of the ultrasonic signal received by the receiver for controlling the lamp brightness.
The very high input impedance, very low input current and very high-speed with reliable performance is provided by operational amplifier IC2 because it has gate operated MOSFET transistor in its input circuit.
The output of operational amplifier (IC2) is given to pin 13 of 5-stage Johnson decade counter CD4017 (IC3). For each pulse from the op-amp, the output of IC3 changes sequentially from Q0 to Q9. The each output Q0 to Q9 is connected to variable resistor VR3 to VR12 through switching diode D3 to D12 respectively. The other end of variable resistor is shorted as shown in receiver circuit diagram (Fig. 3). The shorted output is connected to emitter of UJT (T3) through capacitor C7. The combination of capacitor C7 at the emitter of the UJT forms a relaxation oscillator around UJT.