The design of the HMI is a very important deciding factor when consumers choose a product. The touch experience of HMI can easily affect the favorability of consumers. How to improve and enhance the touch performance of HMI has become the focus of market competition.
Capacitance, inductance, resistance can be used to achieve touch sensing technology means, like inductive devices can be used to coil self-inductance or mutual inductance coefficient of change to replace many mechanical button applications. Capacitive technology is more widely used and has become the preferred choice in the vast majority of designs.
Challenges of Size and Power Consumption
Although the principle of capacitive sensing is not at all complex, capacitive touch has enabled very sophisticated feedback. For example, features such as gesture recognition support, waterproofing, wrist detection and gloved touch can now be realized through capacitive sensing technology, enhancing the interaction experience between consumers and products.
Devices with touch screensTouch screen design is a major factor in attracting consumers, and the human-computer interaction experience is a key differentiator for manufacturers. Under the premise of ensuring the accurate response ability of touch sensing, the market competition in this field mainly centers around two major design directions. One is better battery life, reduce touch screen power consumption; the second is to realize more functions in a small size.
Touch-sensitive function is a device will be on for a long time, as long as the device is not off state, the function has been in the open state. Because the user's interactive behavior is unpredictable, can only be maintained throughout the response. Therefore, the power consumption of the touch sensor function is very influential to the overall power consumption of the device.
Now more and more functions are based on touch sensing to realize, in the size of the screen is limited, add these rich features and can not reduce the response speed and reliability of touch sensing is also a difficult problem. The sensitivity of the touch sensing element is positively correlated with its size, and the introduction of more functionality should not be at the expense of sensing performance.
Which sensing technology to choose to meet market challenges
Touch sensing technologies, still more diverse, each with different characteristics. Choosing the right sensing technology has a significant impact on the experience of using touch sensing.
Such as inductive sensing, is the use of coil self-inductance or mutual inductance coefficient of change to realize the non-electrical power measurement, in the field of automation has a lot of use cases. Inductive touch devices began a long time ago in wearable devices HMI and industrial HMI instead of mechanical button applications, with the development of touch sensor technology now inductive touch devices in industrial HMI there are many applications, consumer applications are not much.
Inductive technology in the touch button advantage is that does not require metal contacts and gaskets such as moving parts, the size can be done very small, and now also developed more functionality, such as through the pressure detection to realize the function of multi-level button.
Resistive touch technology utilizes a film that bends when it comes into contact with pressure, the surface electrode film bends and comes into contact with the electrode film underneath, thus generating an electric current that is detected. The advantages and shortcomings of this technology are obvious, the advantage is that any object that can exert pressure can trigger touch sensing, plus the cost is very low, so it is widely applicable.
But the technology at the same time slower response, also does not support multi-touch, want to realize more features in the HMI almost nothing to expand the place.
Capacitive touch, now the absolute mainstream technology, touch capacitance between the distance between the poles of a certain change, so that the capacitance changes, the technology can be subdivided into self-capacitive induction and mutual capacitive induction. Self-capacitance uses a conductor connected to the MCU and measures the capacitance between that pin and the power ground at the time of triggering, and this technique is generally used for single-touch or slider. Mutual capacitance sensing, on the other hand, is two direct measurements of the capacitance change between two electrodes, and can detect multi-finger touch touch screens at the same time.
Capacitive touch response speed, responsive, is now smart phones, tablet PCs, smart wearables, home appliances and other areas are very favored technology. Although the cost is high, its multi-functional implementation and the convenience brought by advanced multi-touch are the prerequisites for making differentiation.
Summary
HMI touch technology has become an indispensable key part of many device designs. Regardless of which technology route is chosen, how the touch chip can enhance anti-interference capability, improve sensitivity, and optimize low power consumption and fast wake-up at the same time of high reliability are the key factors to enhance the touch experience.