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Wireless Switch Circuit Diagram

Summary

By: 
Anjali Sethiya

Normally, home appliances are controlled by means of switches, sensors, etc. However, physical contact with switches may be dangerous. The circuit described here requires no physical contact for operating the appliance. You just need to move your hand over the light dependent resistor (LDR). The device connected to it switches “on” when you put your hand over the LDR and remains “on” until you again move your hand over it.

The wireless switch circuit is based on two ICs: one is operational amplifier LM741 and JK Flip Flop CD4027. An op-amp produces an output voltage that is hundreds of thousand times larger than the voltage difference between its input terminals. CD4027 is a master slave JK flip flop IC which works in toggle mode. Here this IC can be used to change the state by the signal applied to one or more control inputs and will have one or two outputs. CD4027 has four inputs namely J, K, Set and Reset and it contain two outputs namely Q and Q bar (Q not).

Wireless Switch Wireless Switch

Description

 

The wireless switch circuit comprises of Operational amplifier LM741 (used as a sensitive voltage comparator), LDR, Preset VR1 (which provides a reference voltage to the non-inverting terminal pin 3 and LDR), R2( connected to inverting pin 2 of IC1) and few more components.

Working: When we do not put our hand on LDR device remains off and as a result pin 2 of IC1 goes high. Consequently, output pin 6 of IC1 remains low.

As soon as anyone puts his hand over LDR, pin 2 of IC1 goes low in comparison to pin 3 of IC1 . Pin 6 becomes high thus providing a clock pulse to pin 13 of IC2 which is a flip flop whose stage is controlled by the logic levels present at J and K input with some internal control. Change in state occurs at the positive going transition of the clock pulse. In this, set and reset pins are independent of the clock and they are initiated when a high signal is present on any of the input pins.

The circuit shown is triggered on the leading edge of the switch pulse which means that output changes when you again put your hand over LDR. From the circuit you can see that both J and K are tied to high input so at every negative or positive transition, the clock pulse pin 13 toggles between high to low. This can be verified with the help of the truth table of the JK flip flop. Therefore, when it receives the clock pulse from IC1 due to hand over LDR, transistor connected to pin15 starts conducting and we will receive the output with the help of relay. You can adjust the sensitivity of LDR with the help of VR1.

Circuit Diagram

Components

Resistor Image
Resistor

Resistor is a passive component used to control current in a circuit. Its resistance is given by the ratio of voltage applied across its terminals to the current passing through it. Thus a particular value of resistor, for fixed voltage, limits the current through it. They are omnipresent in electronic circuits.

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Capacitor image
Capacitor

 

 

Capacitor is a passive component used to store charge. The charge (q) stored in a capacitor is the product of its capacitance (C) value and the voltage (V) applied to it. Capacitors offer infinite reactance to zero frequency so they are used for blocking DC components or bypassing the AC signals. The capacitor undergoes through a recursive cycl...

LDR | Light Dependent Resistor
LDR

An LDR (Light dependent resistor), as its name suggests, offers resistance in response to the ambient light. The resistance decreases as the intensity of incident light increases, and vice versa. In the absence of light, LDR exhibits a resistance of the order of mega-ohms which decreases to few hundred ohms in the presence of light. It can act as a sensor, since a varying voltage drop can be obtained...

BC547 | Transistor BC547  | PDF Datasheet
Transistor BC547
BC547 is an NPN bi-polar junction transistor. A transistor, stands for transfer of resistance, is commonly used to amplify current. A small current at its base controls a larger current...
Relay Switch Image
Relay Switch

Relay is an electromagnetic device which is used to isolate two circuits electrically and connect them magnetically. They are very useful devices and allow one circuit to switch another one while they are completely separate....

Video

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