Five ways to design capacitive touch sensors.

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Five ways to design capacitive touch sensors.

Postby maryzhu » Fri Apr 14, 2017 8:39 am

I am an electronic engineer in the field of capacitive touch sensors, In recent days I am making a project for five ways to design capacitive touch sensors. Today I come to this forum to turn to you to discuss my understandings are appropriate.

The project for capacitive touch sensors begins now:

Key is widely used in consumer products, household appliances and industrial systems and other end products. Consumers who are now well versed in technology want to get products with a stylish and reliable user interface. They hope that even simple products should be fashionable and easy to wear and easy to repair.

In the traditional user interface (UI) design is the use of poor reliability and cumbersome attractive mechanical buttons. For these and other reasons, the capacitive sensor keys are gradually starting to replace the mechanical keys. Capacitive sensor keys can be fully integrated into the product design, and will never wear out. Therefore, the user interface based on capacitive touch sensing technology has become the design trend of the current user interface.

However, the design of capacitive touch buttons and the realization of a stable implementation scheme are a very heavy task for system engineers. In this article, we will focus on how to use five simple steps to design a reliable capacitive touch sensor.

Traditional Key system:

Before talking about how to turn the mechanical key system into a capacitive system design, let's take a quick look at the next mechanical key system. Mechanical keys are generally made of materials such as plastic, wood or metal. These systems must be highly reliable because they are susceptible to dust and other environmental factors, and are not wearable. The number of times the machine switch can be recycled determines its service life (and usually also determines the service life of the product). In order to make the mechanical switch to achieve long service life, must be reliable, long time design.

Another factor to be considered in the design is aesthetic design. A lot of mechanical buttons are not attractive and not attractive design, so also need to spend some extra effort to carry out aesthetic design. Since mechanical keys are often protruding from the device, it is not easy to design a stylish and robust user interface system with mechanical keys. And in this regard capacitive sensor keys can greatly simplify this aspect of the design.
However, it is not easy to design a capacitive sensing system. It is much more complicated than designing a mechanical key system because:
    1. In the induction and on / off decision logic will involve a lot of induction parameters.
    2. Capacitive touch sensors are susceptible to external noise.
    The sensing circuit involves a number of hardware parameters, such as reference voltage, source / drain current, clock, and so on. Therefore, the on / off decision logic of the capacitive switch also involves a lot of software parameters such as thresholds. These parameters must be set to optimal values ​​for optimum performance. Selecting the optimal value for these parameters is called tuning. Tuning the capacitive sensing system is a time-consuming and laborious process. Capacitive sensing involves a lot of parameters, so there will be a lot of parameter combinations, which makes tuning work more time-consuming.

Configurable capacitive sensing devices:

Configurable capacitive sensing devices can avoid cumbersome tuning processes. There are some pre-programmed devices with embedded auto-tuning algorithms. The autotune algorithm can tune all the inductive parameters according to the characteristics of the sensor and other sensing elements to achieve the optimum value. This eliminates the need for tuning operations and eliminates the maximum design barrier for capacitive sensors.

In addition, configurable capacitive sensing devices typically support a variety of peripherals and functions such as LED drivers, buzzers, and scan rate control. Configuring these devices means that these functions are enabled / disabled and the parameter values ​​of the active functions are set according to the application needs. Cypress's MBR series of capacitive sensing devices is a configurable device that simplifies the design of capacitive sensing systems. In this series of articles, we can configure the capacitive sensing device MBR device, for example, to explore the capacitive sensor system design.

Ps: Excuse me if I was wrong in words or expressions as I am a green hand in the field of capacitive touch sensors. I need continual learnings.

What is your idea ? Do you agree with my ideas ? Any of your ideas would be highly appreciated.

May someone would like to help ?

thanks in advance.
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