Nowadays, touch buttons are widely used since they are a cool method to control devices.
This article shows how to use a common chip known as the 555 IC to create a simple touch switch.
To make it work you do not require any costly or difficult parts.
For beginners or those who enjoy electronics this project is best choice.
With just one tap you can activate lights, toys or anything else you like with this touch switch!
What is a ON OFF Touch Switch Circuit with Relay:
With the help of a relay an ON-OFF touch switch circuit allows you to control the switching of a load or device by simply pressing a touch sensitive pad.
When the touch input gets detected the relay is used to switch that particular loads status ON or OFF.
This kind of circuit is often used for designing touch sensitive interfaces or in cases in which a physical switch is not required.
Circuit Working:
If you want to switch 220V loads ON/OFF then you must use the following circuit which uses a relay.
The load and the 220V AC input must be wired with the relay contacts appropriately.
Parts list:
| Category | Component | Quantity |
|---|---|---|
| Resistors | 1M CFR | 2 |
| 330Ω CFR | 1 | |
| Capacitors | 0.01μF | 1 |
| Semiconductors | IC 555 | 1 |
| LED | 5mm 20mA | 1 |
| Copper Touch Pads | 4 | |
| Relay | 6V to 9V | 1 |
| Diode | 1N4007 | 1 |
During the initial or idle state the 555 IC remains stable in either the ON or OFF state.
Upon touching the ON copper strips a small negative supply flows through the skin reaching the trigger input pin.
The falling edge detected by the internal comparator and flip flop transitions the flip flop to the set condition resulting in a HIGH output ON state.
Conversely, when touching the OFF copper strips a small positive supply flows through the skin to the threshold pin.
The internal comparators output reaches the reset pin of the internal SR flip flop setting the output state to LOW OFF condition.
Formulas:
Below mentioned are the formulas for Simple ON OFF Touch Switch Circuit with Relay:
The voltage across the sensor (Vsensor) at contact is found using the following formula:
Vsensor = Vin * (Rtouch / (Rpullup + Rtouch))
where,
- Vin is the circuits supply voltage.
- Rtouch as stated in the datasheet is the touch sensors resistance when pushed.
- Rpullup the value of a pull up resistor
How to Build:
To build a Simple ON OFF Touch Switch Circuit with Relay follow the below steps:
- Make sure the notch or dot on the IC matches the notch on the breadboard before inserting the 555 IC into the PCB.
- Connect the power supplies positive and negative terminals to the corresponding PCB rails.
- Connect pin 8 of the 555 IC to the positive supply.
- Connect pin 4 to pin 8.
- Connect pin 5 to Pin 8.
- Connect pin 2 to the touch plate for ON.
- Connect pin 6 to the touch plate for OFF.
- Connect pin 7 to Pin 6.
- Connect pin 3 to the output component LED or Relay.
- Connect pin 1to the negative supply.
- Use four copper strips as touch plates.
- Place two plates close together within a 2mm gap for ON touch.
- Connect these two plates to the negative supply.
- Place the other two plates close together for OFF touch.
- Connect these two plates to the positive supply.
- For the LED based circuit connect a current limiting resistor in series with the LED.
- Connect the LEDs other end to pin 3.
- Wire the relay coil between pin 3 and the positive supply in the relay based circuit.
- To control external devices connect the relay contacts.
- Power the circuit.
- To see the LED or relay go between ON and OFF states, alternately touch the ON and OFF plates.
Conclusion:
This Touch Controlled One Touch ON/OFF Switch enables you to easily control devices with just a touch.
Your electronic projects will have a secure and adaptable solution thanks to the use of the adjustable 555 IC and the thorough building and functioning rules offered.
Try new things, be creative and experience how easy touch controlled technology is.