- As human beings have five sense elements that help humans to know their surroundings and interact, similarly machines can also interact with their surroundings if machines can learn to sense their surroundings, and this can be done by various sensor.
- The invention of the first manmade sensor, the thermostat, dates back to 1883. In the 1940s infrared sensors were introduced. Today we have sensors that can sense motion, light, humidity, temperature, smoke, etc. Analog and digital both types of sensors are available today. Sensors have brought a revolutionary change in the size and cost of various control systems. One such sensor which can detect touch is the Touch sensor.
- Touch sensor has been common nowadays for displays and IoT projects with Arduino. They can be found in lamps, touch screens of smartphones, and other wide arrays of applications as well.
- A touch sensor is an electronic sensor used in detecting and recording physical touch. Also known as tactile sensors, it’s a small, simple, low-cost sensor made to replace old mechanical switches we have seen in the past.
Working of Touch Sensor
- A touch sensor works like a switch, where when there’s contact, touch, or pressure on the surface of a touch sensor, it opens up an electrical circuit and allows currents to flow through it.
- These sensors are sensitive to any pressure or force applied or touched. The principle of touch is similar to that of a switch. When the switch is closed, the current flows otherwise there is no chance of the current flowing. Similarly, when the touch sensor senses the touch or proximity is captured then it acts like a closed switch otherwise it acts as an open switch. These sensors are also known as ‘Tactile Sensors’.
Types of Touch Sensor
Capacitive Touch Sensor
- A Capacitive touch sensor measures touch based on electrical disturbance from a change in capacitance. It consists of an electrode film on top of the glass panel that’s conductively coated with a printed circuit pattern around the outer viewing area.
- A capacitive touch sensor contains two parallel conductors with an insulator between them. These conductors’ plates act as a capacitor with a capacitance value of C0.
- When these conductor plates come in contact with our fingers, our finger acts as conductive object. Due to this, there will be an uncertain increase in capacitance.
- A capacitance measuring circuit continuously measures the capacitance C0 of the sensor. When this circuit detects a change in capacitance it generates a signal that is determined as a touchpoint.
- Portable devices such as smartphones and tablets (iPhones, iPad, etc.)
- Home applications such as touch lamps
- Doesn’t require pressure to be applied since.
- It’s built on the glass itself, hence making force insignificant to sensing requirements.
- Support for multi-touch.
- High responsiveness.
- Vulnerable to abrasion.
- Reliability concerns when used in harsh environments.
- Doesn’t work with gloves or a stylus.
Resistive Touch Sensor
- A resistive touch sensor consists of two conductive layers separated by small spacer dots. The bottom layer is made up of either glass or film and the top layer is made up of the film. The conductive material is coated with metallic film generally Indium Tin Oxide and is transparent.
- The resistive touch sensors calculate the pressure applied on the surface to sense the touch.
- These sensors contain two conductive films coated with indium tin oxide, which is a good conductor of electricity, separated by a very small distance.
- Across the surface of the films, a constant voltage is applied. When pressure is applied to the top film, it touches the bottom film. This generates a voltage drop which is detected by a controller circuit and a signal is generated thereby detecting the touch.
- Musical instruments, touchpads, etc.
- Older music players, game consoles, etc.
- Office equipment.
- Cost-effective and durable to be used in harsh environments.
- Able to be used with stylus and gloves.
- Less complex.
- Low power consumption.
- The inability of multi-touch technology unlike the capacitive touch sensor.
- Dependent on pressure, require more pressure to be applied for sensing to take place.
- Some of the examples of touch sensors available in the market are TTP22301, TTP229, etc.