Arduino interfacing with capacitive touch sensor

  Arduino interfacing with capacitive touch sensor

1.    Digital touch sensor

    A capacitive touch sensor is same as our android phone screen. Capacitive touch sensing is a way of human touch sensing, that requires little or no force to activate. It may be used to sense human touch through more than a quarter of an inch of plastic, wood, ceramic or other insulating material (not any kind of metal though), enabling the sensor to be completely visually concealed.

    Specifications of touch sensor:  - This touch sensor is a capacitive touch sensor which                 works on active capacitor which get create when any person touches it, just like our phone                   screen.

                       

                         Pins of Sensor: -

                         ·     Input supply voltage: 5v.

                   ·    Ground: GND supply.

                   ·   Data output: Digital data output.

2.    Working of touch sensor

    Touch sensors are also called as tactile sensors and are sensitive to touch, force or pressure. They are one of the simplest and useful sensors. The working of a touch sensor is similar to that of a simple switch. When there is contact with the surface of the touch sensor, the circuit is closed inside the sensor and there is a flow of current. When the contact is released, the circuit is opened and no current flows.

The simplest form of capacitor can be made with two conductors separated by an insulator. Metal plates can be considered as conductors. The formula of capacitance is shown below.

C = ε₀ * ε_r * A / d

Where

ε₀ is the permittivity of free space

ε_r is relative permittivity or dielectric constant

A is area of the plates and d is the distance between them.                        

Capacitance is directly proportional to the area and inversely proportional to the distance.

In capacitive touch sensors, the electrode represents one of the plates of the capacitor. The second plate is represented by two objects: one is the environment of the sensor electrode which forms parasitic capacitor C₀ and the other is a conductive object like human finger which forms touch capacitor C_T. The sensor electrode is connected to a measurement circuit and the capacitance is measured periodically. The output capacitance will increase if a conductive object touches or approaches the sensor electrode. The measurement circuit will detect the change in the capacitance and converts it into a trigger signal.

The working of a capacitive touch sensor is shown in below figure.

                                                  Figure 3: How capacitive sensor works.

3.    Component needed in project

    In this project we are interfacing a capacitive touch sensor with Arduino to know that how does it actually work and simple project like a switch alarm system is made. This project would need below described component.

·         Arduino board.

·         Touch sensor.

·         Led and resister.

·         Buzzer.

·         Jumper wire.

   Figure 4: Component for project.

4.    Arduino interfacing with touch sensor

    A capacitive touch sensor is very  sensitive and system measure the time for which touch screen is kept in touch with user hand.

         In this project we would lean to interface touch sensor with Arduino.

         And signal pin of touch sensor can be connected to any pin you want just you have

         to  change it Arduino code as input pin.

       

         Pin connection of sensor and Arduino board.

S no.	Touch sensor	Arduino
1	VCC	+5v pin
2	GND	GND
3	Signal	D2

Figure 5: touch sensor with Arduino uno.

Note: - When the capacitive sensor is not touch then it will give high output voltage and when it get         touch by finger a capacitive field get created with earth and it start giving low output.

5. Arduino code for capacitive sensor: 

    download code from here:  Arduino board code for Capacitive touch sensor Alarm.

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