Touch buttons are everywhere these days they are a cool way to control things.
This guide shows you how to make a simple touch switch using a common chip called the 555 IC.
You do not need any fancy or expensive parts to make it work.
This is a great project for beginners or people who like electronics.
You can use this touch switch to turn on lights, toys or anything else you want with just a tap!
What is a ON OFF Touch Switch Circuit with Relay:
An ON-OFF touch switch circuit with a relay is an electronic circuit that allows you to control the switching of a device or load by simply touching a touch sensitive pad.
The relay is used to toggle the state ON or OFF of the connected load in response to the touch input.
This type of circuit is often used for applications where a physical switch is not desired or for achieving a touch sensitive interface.
Circuit Operations:
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:
The voltage across the sensor (Vsensor) at contact may be 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
Circuit Construction:
- Insert the 555 IC into the PCB, ensuring that the notch or dot on the IC aligns with the notch on the breadboard.
- Connect the positive and negative terminals of the power supply to the appropriate rails on the PCB.
- 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 other end of the LED to pin 3.
- For the relay based circuit, connect the relay coil between pin 3 and the positive supply.
- Connect the relay contacts to control external devices.
- Apply power to the circuit.
- Touch the ON and OFF plates alternately to observe the LED or relay switching between ON and OFF states.
Conclusion:
By implementing this Touch Controlled One Touch ON/OFF Switch, you can seamlessly control devices with a mere touch.
The use of the versatile 555 IC, along with the detailed construction and working principles provided ensure a reliable and customizable solution for your electronic projects.
Experiment, innovate and enjoy the simplicity of touch controlled technology.