@▷ Alarm System Using Radio Waves | Diagram for Schematic

Alarm System Using Radio Waves


The circuit was designed to provide an alarm system that would transmit signals across the medium wave or the radio wave.


Medium Wave – operates within the frequency range of 515 kHz to 1629 kHz which is part of the medium frequency radio band
CMOS 4093 – a quad 2-input NAND with Schmitt trigger inputs integrated circuit, generally characterized by small fluctuation in voltage supply, very high impedance, outputs that can sink and source, one output can drive up to 50 inputs, high speed gate propagation time, high frequency, and low power consumption

Circuit Explanation

Using radio waves, even the detection far from the alarm is possible, because radio waves have the longest wavelengths in the electromagnetic band which can reach between 100 and 1000 meters. The sensor may be made of tin foil, coupling with the IC1a to produce an oscillation at around 1 MHz. this frequency will be modulated by the IC1b which produces audio frequency in the form of nonstop beep. As the sensor detects any approaching object, the frequency of the transistor IC1a will fall drastically. During this incident, a beep will be heard on the radio. The radio will not react when the frequency of the circuit plays around 1 MHz. The use of CMOS 4093 is to provide good noise immunity which is ideal for noisy signals and slow changes. This IC provides the functions of a Schmitt trigger where it switches the output negative when the input passes through a positive reference voltage and uses a negative feedback to avoid switching back to the previous state.

To illustrate the operation in another way, if an antenna will be attached to the mains by means of connecting a multiplug adapter, this can prove that every wire in the house is transmitting on the medium wave band. Using this method can lead to setting up an early warning device with the use of a properly tuned medium wave radio.

The sensors may be represented in some forms other than the tin foil such as burglar bars or door knobs. This alarm system may also be controlled using a push button switch that will reduce the frequency of IC1a and activate the system alarm. It may be done by connecting a 33K ohm resistor in series and would require a tuned radio with a frequency lower than the transmitter.


Radio waves are being utilized in almost every equipment necessary to humans like the television system where it receives signals electromagnetic waves through the antenna; the cellular phone system where radio waves transmit information; the radio telescopes because radio waves are larger than optical waves; in radio astronomy where radio frequencies are used to study celestial objects; and in ship navigation where radio compass, radio time signal, and radio range are typically used.

Similarly, medium frequencies play a vital role in humans like the navigational radio beacons for aircraft and maritime distress and emergency; in AM broadcast communication; in amateur radios and in cordless telephones.

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