The Touch ON and OFF Switch Circuit utilizes a 555 timer and leverages the default properties of the 555 Timer IC pins. This circuit enables you to activate or deactivate a device simply by touching the designated Touch Plates.
When strategically positioned, these touch plates eliminate the need to physically move to operate the device.
An important safety feature of this circuit is its ability to prevent electrical shocks, a potential risk with traditional switches, even when utilizing touch plates.
As mentioned earlier, the core of this circuit is the 555 Timer IC. Other vital components include a relay module and the touch plates, which we will demonstrate how to create for this project.
Outline
- Circuit Diagram
- Components Required
- How to make the Touch Sensor (Touch Plate)?
- Circuit Design
- Principle behind the Project
- Working of the Project
- Applications
Circuit Diagram
The circuit diagram for the touch ON and OFF switch circuit is shown in the below image.
Components Required
- 1 x 555 Timer IC
- 1 x 3.3 MΩ Resistor (1/4 Watt)
- 1 x 1 MΩ Resistor (1/4 Watt)
- 1 x Bulb with holder (regular or CFL)
- 1 x 5V Relay Module (if relay module is not available, then you need the following components)
- 1 x 5V Relay
- 1 x 2N2222 NPN Transistor
- 1 x 1N4007 PN Junction Diode
- 1 x 1 KΩ Resistor (1/4 Watt)
How to make the Touch Sensor (Touch Plate)?
The Touch Plates or Touch Sensors play a pivotal role in this project, as they are the key to toggling the gadgets on and off. Fortunately, you don’t need to invest in expensive or elaborate touch sensors for this endeavor. We will guide you on crafting a simple touch plate.
To accomplish this, you’ll require two small copper-coated boards. In our project, we’ve employed two 2cm × 2cm copper-clad boards.
Next, the objective is to create a thin, deep groove down the center of each board, essentially dividing the copper on both ends without completely severing it. The illustration below depicts both the bare copper-clad board and the two boards with a central groove.
Another option is to repurpose touch plates from old toys and doorbells. Typically, touch pads consist of a small carbon block embedded in silicone rubber.
When you press the button, this block makes contact with the pad, thereby reducing the resistance between the two interlocking tracks.
Commercially available pads are designed to resist corrosion and exhibit excellent sensitivity in detecting your finger’s response.
When you place your finger between the contact points, the pressure and moisture on your finger cause the resistance between these lines to decrease, typically ranging from 150k to 850k.
Circuit Design
The Touch ON and OFF Switch circuit boasts a very straightforward design. Initially, the GND, VCC, and RST pins of the 555 timer (pins 1, 8, and 4) are connected to the ground (GND) and a 5V power source, respectively. Pin 2 is connected to ground through a 3.3 M resistor to maintain a high signal, while Pin 6 is connected through a 1 M resistor for the same purpose.
In accordance with the circuit diagram, pins 2 and 6 are linked to two touch plates. When contact is made with the ON plate, one end connects to Pin 2, while the other end connects to ground (GND). Likewise, when the OFF plate is touched, one end connects to +5V, and the other end connects to Pin 6.
Principle behind the Project
The project’s core premise is based on the basic functionality of the 555 Timer’s pins. GND (1), Trigger (2), Output (3), Reset (4), Control Voltage (5), Threshold (6), Discharge (7), and VCC are the eight pins of a 555 Timer (8).
Pins 2 and 6 are employed in this project. We can now see how these pins work in their most basic form. The output of the 555 Timer IC will be HIGH and stay there if Pin 6 (the Threshold pin) is held LOW and Pin 2 (the Trigger Pin) is made LOW. The appliance can be turned on using this condition.
Now consider Pin 2 is pulled HIGH and if Pin 6 is made HIGH. The output of the 555 Timer IC will be LOW and it stays there. This condition can be used in our project to turn OFF the load or device.
Working of the Project
- Apply the power supply and connect the circuit as shown in the diagram.
- To turn the gadget “ON,” place your finger on the “ON” plate, and to turn it “OFF,” place your finger on the “OFF” plate.
- The device connected through the relay (we have attached a light bulb) remains OFF when electricity is introduced to the circuit. Pin 2 is now pulled HIGH, while Pin 6 is pulled LOW, as seen in the circuit diagram.
- The voltage at Pin 2 (Trigger Pin) of the 555 IC becomes LOW when we touch the ON plate. The output at Pin 3 becomes HIGH because Pin 6 is already LOW.
- Because the Transistor is connected to the Relay Module, the Transistor will be turned on, which will activate the Relay. As a result, the device becomes operational.
- The voltage at pin 6 is zero at this moment because it is pushed low by default, while the voltage at pin 2 is HIGH.
- When you contact the OFF plate, the Pin 6 receives +5V for a limited period of time, causing the 555 Timer IC’s output to turn LOW.
- The transistor and the relay will both be turned off as a result of this. As a result, the gadget will be turned off.
- This circuit operates by pressing a button to turn a relay to the “ON” state, and then pressing the button again to turn the gadget off. It works in the same way as a flip-flop.
Applications
- A simple Touch to ON and Touch to OFF Switch Circuit is designed in this project using which, we can turn ON or OFF any device by simply touching the pads.
- By isolating the touch plates from the actual circuit, we can create a nice looking touch controls for our appliances.
