Radio - Wireless

Wireless Switch Circuit using CD4027


  • Introduction 
  • Circuit Principle 
  • Circuit Diagram of Wireless Switch Circuit using CD4027
  • Components Required
  • Circuit Design
  • Wireless Switch Circuit Working


In this project, I will show how to operate any electrical without making physical contact with switch by implementing a Wireless Switch Circuit using CD4027 IC.

Electrical and electronic gadgets that we use in our homes are typically controlled by switches, which we flip to turn the appliance ON or OFF. However, in this project, I will demonstrate an intriguing method of controlling any device, such as a light bulb.

The approach used here employs a Wireless Switch Circuit, in which the device (such as a lamp) is turned on by sliding our hand in front of the circuit, and the device is turned off by sliding our hand again.

You may avoid the dangers of having personal touch with the switches by using this easy Wireless Switch Circuit.

Circuit Principle 

The main principle of this Wireless Switch Circuit is in the functioning of LDR, LM741 Op-Amp and a CD4027 JK Flip-Flop IC. In this circuit, all you  need is to pass your hand above a simple Light Sensor, the infamous LDR.

The LDR is configured in such a way that, light from an LED will continuously fall on the LDR and when you place your hand over (or pass your hand between the LED and LDR), the device connected to the circuit will turn ON. 

This change is detected by an Op-Amp (LM741 is used here) and triggers a flip-flop (CD4027 is used). The device will stay turned ON untill you pass your hand over the LDR again. 

Circuit Diagram of Wireless Switch Circuit using CD4027

Wireless Switch Circuit using CD4027

Components Required

  • CD4027 – 1
  • LM741 – 1
  • Resistors
    • 10KΩ – 3
    • 33KΩ – 1
    • 1KΩ – 1
  • LDR
  • LED
  • 5V Relay Module
  • Lamp

Circuit Design

The circuit is designed in a fairly straightforward manner. To begin, attach a voltage divider (either two resistors or a potentiometer) to the Op-Amp LM741’s Inverting terminal (Pin 2). Connect the LDR and a resistor (which together create another voltage divider) to the Op-Non-Inverting Amp’s terminal (Pin 3).

Place an independent LED in front of the LDR (with a current limiting resistor) so that the light from the LED always falls on the LDR.

Connect the output (Pin 6) of the Op-Amp to the clock (Pin 13) of the Flip-Flop IC CD4027. The output of the Flip-Flop (Pin 15) is connected to the Relay Input of the 5V Relay Module. 

Finally, connect the J (Pin 10) and K (Pin 11) Pins of CD4027 to +5V and Set (Pin 9) and Reset (Pin 12) to GND. Rest of the connections with respect to power supply are self explanatory. 

NOTE: In place of two fixed resistors that are connected to the Inverting Input of the Op-Amp, you can connect a Potentiometer and vary the sensitivity of the circuit. 

Wireless Switch Circuit Working

The circuit’s operation is relatively simple to comprehend. The circuit is mostly based on two integrated circuits. The first is an Operational Amplifier (LM741). For sensing LDR voltage and a reference voltage, the LM741 Op-Amp is used as a comparator.

The JK Flip-Flop IC CD4027 is another option. It’s made up of two JK Flip-Flops, each having its own Set and Reset pins. When a signal is applied to any of the input terminals, the CD4027 is utilised to change the state and can provide several outputs.

Under typical circumstances, the Op-output Amp’s is constantly LOW because the LDR receives light from the LED on a continuous basis.

As soon as someone passes their hand over the LDR, Pin 3 of the Op-Amp will be at a greater voltage than Pin 2, causing Pin 6 to become High for a brief period of time.

Pin 13 of the CD4027 receives this HIGH condition as a clock pulse (flip flop IC). Because the flip-J flop’s and K inputs are both coupled HIGH, a clock pulse will toggle the Output, making it HIGH.

Because the CD4027’s output pin is connected to the relay’s input, the lamp connected to the relay will turn on.

If you pass your palm over the LDR again, the process will repeat itself, with the CD4027 IC’s output being LOW this time (Toggle from HIGH to LOW).


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