Electronics >> Schematics Depot >> IR/Ultrasonic >> ultrasonic switch
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|IC1||NE555 timer IC|
|VR1||10k variable resistor|
|R4, R5||220 ohm resistor|
|C1||680 picofarad capacitor|
|D1, D2||1N4148 Diode|
|T1||SL100 NPN transistor|
|T2||SK100 PNP transistor|
|S1||SPST momentary contact switch|
|XMTR||ultrasonic transmitter 40-50khz|
|RCVR||Ultrasonic Receiver 40-50khz|
|RL1||6volt 200ohm resistor|
|VR2||250k Variable Resistor|
|R8, R12||15k Resistor|
|R15||33 ohm Resistor|
|C3||0.22uf ceramic capacitor|
|C4||0.1uf ceramic capacitor|
|C5||560n ceramic capacitor|
|T3,T4||BC548 NPN Transistor|
|T5||BC558 PNP Transistor|
|T6||SL100 NPN Transistor|
all resistors are 5 or 10 percent tolerance, 1/4-watt
all capacitors are 10 percent tolerance,
rated 35 volts or higher
The circuit described generates (transmits) ultrasonic sound of frequency between 40 and 50 kHz.
As with any other remote control system this cirucit comprises of a mini transmitter and a receiver circuit. Transmitter generates ultrasonic sound and the receiver senses ultrasonic sound from the transmitter and switches on a relay.
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The ultrasonic transmitter uses a 555 based astable multivibrator. It oscillates at a frequency of 40-50 kHz. An ultrasonic transmitter transducer is used here to transmit ultrasonic sound very effectively. The transmitter is powered from a 9-volt PP3 single cell.
The ultrasonic receiver circuit uses an ultrasonic receiver transducer to sense ultrasonic signals. It also uses a two-stage amplifier, a rectifier stage, and an operational amplifier in inverting mode. Output of op-amp is connected to a relay through a complimentary relay driver stage. A 9-volt battery eliminator can be used for receiver circuit, if required.
When switch S1 of transmitter is pressed, it generates ultrasonic sound. The sound is received by ultrasonic receiver transducer. It converts it to electrical variations of the same frequency.
These signals are amplified by transistors T3 and T4. The amplified signals are then rectified and filtered. The filtered DC voltage is given to inverting pin of op-amp IC2. The non-
inverting pin of IC2 is connected to a variable DC voltage via preset VR2 which determines the threshold value of ultrasonic signal received by receiver for operation of relay RL1.
The inverted output of IC2 is used to bias transistor T5. When transistor T5 conducts, it supplies base bias to transistor T6. When transistor T6 conducts, it actuates the relay. The relay can be used to control any electrical or electronic equipment.
1. Frequency of ultrasonic sound generated can be varied from 40 to 50 kHz range by adjusting VR1. Adjust it for maximum performance.
2. Ultrasonic sounds are highly directional. So when you are operating the switch the ultrasonic transmitter transducer of transmitter should be placed towards ultrasonic receiver transducer of receiver circuit for proper functioning.
3. Use a 9-volt PP3 battery for transmitter. The receiver can be powered from a battery eliminator and is always kept in switched on position.
4. For latch facility use a DPDT relay if you want to switch on and switch off the load. A flip-flop can be inserted between IC2 and relay. If you want only an ‘ON-time delay’ use a 555 only at output of IC2. The relay will be energised for the required period determined by the timing components of 555 monostable multivibrator.
5. Ultrasonic waves are emitted by many natural sources. Therefore, sometimes, the circuit might get falsely triggered, espically when a flip-flop is used with the circuit, and there is no remedy for that.