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 demonstrate how to operate any electrical device without the need for physical contact with a switch by implementing a Wireless Switch Circuit using the CD4027 IC.

Typically, we control electrical and electronic gadgets in our homes using switches that we flip to turn the appliances ON or OFF. However, in this project, I will showcase an intriguing method for controlling any device, such as a light bulb.

The approach I will use here involves utilizing a Wireless Switch Circuit, where the device (like a lamp) can be activated by simply sliding a hand in front of the circuit, and deactivated by repeating the hand gesture.

This easy Wireless Switch Circuit allows you to avoid the hazards associated with direct contact with switches.

Circuit Principle 

The main principle behind this Wireless Switch Circuit involves the operation of the LDR, LM741 Op-Amp, and a CD4027 JK Flip-Flop IC. In this circuit, you only need to move your hand above a simple Light Sensor, which is the notorious LDR.

The LDR is configured in a manner where light from an LED continually shines on it. When you position your hand over (or pass your hand between the LED and LDR), the circuit activates the connected device.

An Op-Amp (specifically, the LM741 in this setup) detects this change and triggers a flip-flop (utilizing the CD4027). The device remains powered ON until you once again move your hand over the LDR.

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’s design follows a relatively simple approach. To start, connect a voltage divider, which can consist of either two resistors or a potentiometer, to the Inverting terminal (Pin 2) of the LM741 Op-Amp. Next, link the LDR and a resistor, forming another voltage divider, to the Non-Inverting terminal (Pin 3) of the Op-Amp.

Position an individual LED in front of the LDR, accompanied by a current-limiting resistor, to ensure a constant illumination of the LDR by the LED’s light.

Connect the Op-Amp output (Pin 6) to the clock input (Pin 13) of the CD4027 Flip-Flop IC. Then, link the Flip-Flop’s output (Pin 15) to the Relay Input of the 5V Relay Module.

Lastly, establish connections by attaching the J (Pin 10) and K (Pin 11) Pins of the CD4027 to +5V, and the Set (Pin 9) and Reset (Pin 12) to GND. The remaining power supply connections 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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