Touch Sensor working principle
The Touch Sensor are sensitive to touch, pressure as well as force. The Touch Sensor works similar to that of a simple switch.
When there is contact or a touch on the surface of the Touch Sensor, in that condition it acts like a closed switch and allows the current to flow through it. When the contact is released it acts similar to the opened switch and hence there is no flow of current.
In the below picture you can understand how the touch sensor works.
Working of different Touch Sensors
Below is the working of the two type of sensors are explained in detail.
Capacitive touch sensor
The Capacitive touch sensors are very popular since they are more robust, durable and user friendly. Moreover, it is also cost-effective when compared resistive touch sensors.
The Capacitive sensor is made just similar to the normal capacitor, that is there are two conductors separated with the insulator.
In case of the sensor the metal plates are used as the conductors and the capacitance of the sensor can be expressed as below.
C = ε0 x εr x A / d
ε0 represents the permittivity of free space
εr represents the relative permittivity or dielectric constant
d represents the distance the parallel plates and A represents the area of the plates.
We know that if the plate has more area the more capacitance it will produce and the more distance between the two plates are the less capacitance will become.
In the Capacitive touch sensor there are the two parallel plates which form a capacitor with the capacitance value represented as C0. As we touch the sensor through our finger, our finger acts like a conductive object and hence produces a capacitance value of CT as shown in the figure below.
In the application of a sensor the capacitance C0 is measured continuously with the help of capacitance measurement circuit. There will be uncertain increase in the capacitance if any conductive object such as our finger touches the plate. The capacitance measuring circuit will detect the change in the capacitance and will convert it into a signal.
If the parallel plates have the more larger area and the thickness of the insulator is very less then there would be the greater value of the touch capacitance (i.e. CT). Therefore the difference of the capacitance value when the plate is touched and the plate is untouched will be greater.
So, by controlling the size of the parallel plate and the thickness of the insulator we can control the sensitivity of the Capacitive touch sensor.
The Capacitive touch sensor however have few drawbacks such as there could be a false trigger since all it needs is to be in a contact with a conducting material and does not require a pressure to operate.
Resistive touch sensor
Like capacitive touch switch, resistive touch sensors are also used in several applications. Though, it’s response time is longer than capacitive touch sensor but it’s control circuit is very simple. It doesn’t depends on the electrical characteristics of capacitance. Due to which, touch panels made by resistive touch can be easily operate by even non-conducting substances such as glove wrapped finger, stylus etc. This touch sensor comes with two conductive layers and each layer is separated by small spacer dots. Resistive touch are also of three types- 4-wire, 5-wire and 8-wire.
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The basic component used in manufacturing a touch screen or panel is a touch sensor, a software drive along with a controller card. A touch sensor comes with mechanical switches powered by switch replacement technology that will help touch modules to be easily used in wide-ranging variety of applications. In addition to this, a touch sensor also comes with rotational or simple linear sliders, along with touch pads as well as rotatory wheels so that all these components together provide huge advantage in producing more intuitive touch based user interfaces. With the day by day improvement in touch sensor technology, it is gradually substituting the mechanical devices such as keyboard, mouse etc.
Working principle of a touch sensor
In present scenario, touch sensors are also known as tactile sensors. The basic working principle of a touch sensor is that it detects near proximity (also known as touch) without depending on physical contact. In simple words, you can understand that its working is same as a simple switch or circuit. When any physical medium came in contact with the touch surface, the internal circuit will be closed inside the sensor and current starts flowing. On the other hand, when this physical contact is broke or released, the circuit will opened and hence, there will be no flow of current. On the basis of several factors like touch response time, cost, material etc, touch sensors can be classified in two categories
- Capacitive touch sensor
- Resistive touch sensor.
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Types of Touch Sensor and its application
You can very easily spot the Touch Sensors in various applications in your daily life.
As per their functions the Touch Sensors are classified into two types which are used in different circumstances and utilities.
Capacitive Touch Sensor
Since these sensors can be produced very easily in a very large scale can be made in very less cost and are very attractive in design. These are widely used in ipods, mobile phones, home appliances, automotive and many other industrial applications. They are used in applications such as measuring pressure, acceleration, distance etc.
Resistive Touch Sensor
Unlike the above these sensors can not sense the small contact or touch. Resistive Touch Sensor require an amount force to operate, so they are used in applications such as Foot pronation monitoring, musical instrument, keypads (mostly used in old mobile phones), resistive touch-pads and many other applications.