The Application of Capacitive Inductive Touch Buttons in Induction Cooker

I. INTRODUCTION Compared to mechanical keys and resistive touch keys, capacitive touch keys are not only durable but inexpensive, simple and easy to install, waterproof and stain resistant, and they also provide functions such as rollers and sliders. However, capacitive touch keys also have many problems. Because there is no mechanical structure, all detections are small changes in the amount of electricity, so they are much more sensitive to various types of interference. ST introduced a capacitive touch sensing solution based on the STM8 series 8-bit general-purpose microcontroller platform for home appliance applications, especially induction cooker applications. Without using a dedicated touch chip, the capacitive touch sensing function can be realized with a simple peripheral circuit. To facilitate the secondary development of customers.

Second, the scheme introduces ST's capacitive touch button program through a resistance and sensing electrode capacitance CX resistance network capacitance charge/discharge time to detect changes in capacitance caused by human touch. As shown in FIG. 1 , when a human hand presses, a capacitance CT is connected in parallel to the sensing electrode, which increases the capacitance on the sensing electrode. The time for the sensing electrode to charge and discharge increases, and the state of the key is detected. The sensing electrode can be directly drawn on the PCB board as a button, roller or slider application style, it can also be made into a spring component inserted on the PCB board, even if the insulating layer (glass, resin) will not detect its performance Affected.

Induction cookers use heating principles based on magnetic field induced currents to heat food. During heating, a strong magnetic field is generated by the coil under the panel. When the magnetic flux passes through the bottom of the pot made by the magnet, the pot cuts alternating magnetic lines of force to generate eddy currents at the bottom of the pot to rapidly heat the pot to heat the food. In this solution, a 44-pin STM8S105S4 is used as the master chip of the key display panel to control the scanning of 13 buttons, the display of 24 LEDs and a 4-bit digital tube, the communication between the I2C and the mainboard, and the convenience of leaving a SWIM interface. Engineers use debugging (Figure 2).

STM8S105S4 uses ST advanced STM8 core, with a 3-stage pipeline Harvard architecture, 3.0 ~ 5.5V operating voltage, internal 16MHz RC can provide MCU 16MHz operating frequency, providing low-power mode and peripheral clock off, a total of 34 I /O available. The STM8S105S4 has 2KB of RAM and 16KB of FLASH, as well as 1KB of EEPROM data memory up to 300,000 erase cycles.