Capacitive touch sensing scheme using common I/O port - Power Circuit - Circuit Diagram

inductance

Nowadays, touch sensing technology is getting more and more attention and application in electronic products. It is not only beautiful and durable, but also has greater sensitivity, stability and reliability than traditional mechanical buttons, and can greatly improve the quality of products. Touch-sensing solutions are attracting more and more attention from IC design manufacturers. New technologies and ICs are constantly available, and domestic companies are launching similar programs. Cpress's CapSenseTM technology is a pioneer in sensing technology and is at the forefront of this field. It is widely used in high-end products. MCP has introduced mTouchTM, AT has also introduced QTouchTM technology, and FSL has introduced electric field sensing. The inductive touch of technology and MCP is also unique, and even ST has QST products.

However, all current touch solutions use dedicated ICs, which is costly and difficult to develop. The RC Acquisition based solution described in this article can be implemented on any MCU and is a revolutionary breakthrough in touch sensing technology. . Firstly, the basic principle of RC charging, as well as the testing and improvement methods of charging time are introduced. Then, the hardware and software design steps based on STM8S single-chip microcomputer are discussed in detail, and the key points are noted.

First, the basic principle of RC charge detection The basic principle of RC charge detection is to measure the charging and discharging time of electrode capacitors such as PCB, and to detect whether there is a 'press' action by comparing the small changes generated during human contact. Choose for any single or multiple buttons, scroll wheels, sliders.

As shown in Fig. 1(a), the periodic charging voltage Vin is applied to the RC network, and Vout is measured to obtain the timing as shown in (b). By detecting the change in the time tc from the start of charging to the time when Vout reaches a certain threshold value, Determine if there is human contact. Figure 2 shows that the charging time becomes longer when there is human contact.

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