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UltraSonic
Switch
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Circuit
of a new type of remote control switch is described here.
This circuit functions with inaudible (ultrasonic) sound.
Sound of frequency up to 20 kHz is audible to human beings.
The sound of frequency above 20 kHz is called ultrasonic
sound. The circuit described generates (transmits) ultrasonic
sound of frequency between 40 and 50 kHz. As with any
other remote control system this cirucit too comprises
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. 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. Important hints:
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. |
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