The Touch ON and OFF Switch Circuit is built around a 555 timer by making use of the default properties of the Pins of the 555 Timer IC. With the help of this circuit, you can turn ON and OFF a device by simply touching the Touch Plates.
If the touch plates are placed at a convenient location, we do not require to move from our place to turn on and off the device.
And the important feature of this circuit is that you will not get any electrical shock which we sometimes get while using the normal switches, even though we are using touch plates.
As mentioned earlier, we have designed this circuit using a 555 Timer IC. The other important components are a relay module and some touch plates (we will show you how to make the touch plates used in this project).
- 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)?
Touch Plates or Touch Sensors are an important aspect of this project because it is relied on a touch to turn on and off the gadgets. We won’t need any expensive or fancy touch sensors for this project because we’ll show you how to create a simple touch plate.
Two little copper coated boards are required to complete the job. We’ve used two 2cm × 2cm Copper clad boards in this project.
Now we need to make a thin, deep cut down the middle of the boards to get two halves on the board without breaking it totally. On both ends, this cut should entirely separate the Copper.
The following image will show the bare Copper Clad board and two boards that have a groove in the middle.
You can also use the touch plate from the old toys and doorbell. Generally touch pads are made of a small carbon block mounted in silicon rubber.
When the button is pushed, this block comes in contact with the pad. Thus resistance between the two interleaved tracks is reduced.
The pads which are available in market are protected from corrosion and have very good sensitivity to detect your finger response.
When the finger is placed between the points, because of pressure and moisture in the finger resistance between these lines drops between 150k to 850k.
Circuit Design
The Touch ON and OFF Switch circuit has a very basic design. To begin, the 555’s GND, VCC, and RST pins (pins 1, 8, and 4) are connected to GND and 5V, respectively. A 3.3 M resistor is used to pull Pin 2 HIGH, while a 1 M resistor is used to pull Pin 6.
As indicated in the circuit schematic, pins 2 and 6 are linked to two touch plates. In the event of a contact to the ON plate, one end is connected to pin 2 and the other to GND. Similarly, the touch to OFF plate has one end linked to +5V and the other end 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.
