CapSense technology uses the principle of capacitive sensing to determine the presence or absence of a finger or other conductor, which is implemented by Cypress PSoC. This new way can replace mechanical buttons, mechanical sliders, membrane keyboards and more. Typical applications for capacitive sensing are buttons, sliders, touchpads, touch screens, proximity sensors, etc. The Sensor can be copper foil on a PCB. The principle of capacitive sensing is that there is parasitic capacitance between adjacent wires or copper foil on the PCB. It can be called Cp. The size of Cp is related to the type of cover. When there is a finger approaching or touching the copper foil, it is equivalent to adding two The capacitor is connected in parallel on Cp. By detecting the change of the capacitance, it can be determined whether there is a finger. This is the basic principle of capacitive sensing.
There are two ways to implement CapSense, CSA and CSD. CSA is the abbreviation of CapSense Successive Approximation. CSD is the abbreviation of Sigma-Delta Modulated Capacitance (CapSense Sigma-Delta Sigma Delta).
CapSense application in white goods
CapSense sensing has many advantages and is ideal for white goods. White goods are household items, aesthetics and performance are the first requirements, in addition to waterproof, anti-jamming and many other requirements, CapSense can be satisfied. In addition, white goods also need a lot of other controls, such as LCD control, motor control, temperature control, water level control, etc. Cypress PSoC can achieve all of the above requirements. Let's take a look at how PSoC CapSense implements these requirements one by one.
Aesthetics and performance
Comparing the touch buttons with the traditional mechanical buttons, the touch buttons are more fashionable and beautiful; no extra buttons are needed, which saves space; in addition, Cypress PSoC can control other functions in addition to touch buttons. Therefore, the overall cost is low; if the touch button is not used, if the PCB is not damaged, the button will not be destroyed, thereby ensuring a longer service life; in the waterproof performance of the white appliance, the touch button also highlights the advantage. The following table compares the two buttons:
Currently, the widely used touch buttons/touch screens mainly have two key technologies, namely resistive and capacitive. Capacitive sensing technology has become the first choice for touch control due to its durability and easy implementation at low cost. Let's compare the two touch technologies. First, the capacitive touch screen only needs to be touched, and no pressure is needed to generate the signal. Moreover, the capacitive touch screen needs only one or no correction after production, and the resistance technology requires regular correction. Mainly because the ITO material is exposed to the air or air barrier, which will cause a change in resistance; the life of the capacitor solution will be longer, because the components in the capacitive touch screen do not need to be moved; in the resistive touch screen, the upper film needs to be thin enough. In order to be elastic, in order to bend down to the underlying film, it is easily damaged. The table below compares these two techniques.
Waterproof design
In white goods, waterproof design is the key. Let's take Cypress PSoC as an example to show how to achieve waterproof effect.
The three sensors are used to describe the waterproof design of the buttons. They can be designed so that the Sensor board and the PCB board are separated, so that the Sensor board can better distinguish different conditions, such as whether water drops appear on the board.
The Sensor board is designed with three touch buttons in the center, two protective Shield Electrodes and one Guard Sensor. The protective electrode of the inner ring is used to prevent misjudgment of the water droplet by the touch button, and the protection sensor is used to judge the presence or absence of the water flow, and the outer ring protection electrode can prevent the sensor from misjudge the water drop.
Anti-jamming design
Anti-jamming design is also one of the key considerations for white goods, to see how Cypress PSoC is done.
In the CSA design, the anti-jamming capability is embodied in two aspects. First, a switched capacitor circuit is used, which forms a low-resistance path with an external modulation capacitor. The noise on the sensing capacitor reaches the modulator due to the low-resistance path. It has been greatly attenuated before. In addition, the CSA mode is divided into three stages. The phase 1 induction capacitor is connected to the internal analog bus to complete the initialization work. The Cmod is restored to the initial voltage VStart through the switched capacitor; the phase 2 is the scanning phase, and the switch circuit is partially disconnected. The Cmod is charged by the constant current source, the counter starts counting until the Cmod voltage reaches the comparator reference voltage, the flipping occurs, and the counting ends; in stage 3, the scanning ends, and the firmware processes the counter data. At the end of these three phases, a scan is completed and then the next scan is taken. The sensing capacitor Cx is only connected to the internal bus in phase 1. In the real measurement counting phase, phases 2 and 3 are both disconnected, so the noise on Cx will not affect the counting, so the anti-interference ability is greatly improved.
CSD has also been specially designed for anti-jamming, which has significantly improved various noise and static interference. First, like CSA, the switching circuit can form a low-impedance path with the external modulation capacitor. The noise on the sensing capacitor has been greatly attenuated before reaching the modulator due to the low-resistance path; the frequency range of the intermediate frequency noise is covered. The operating frequency range of PSoC, so when the frequency or harmonic component of the noise is the same as the frequency of the switched capacitor module, the charging current of the modulator changes, causing the counter data to change. CSD uses a pseudo-random sequence generator to control the switching of switches 1 and 2, so that it can have good resistance to intermediate frequency noise; ultra-high frequency noise can be attenuated by connecting a resistor in series with each I/O port of each sensor and a capacitor in parallel; ESD will cause the protection diode of the PSOC GPIO to turn on instantaneously, which will cause the counter value to fluctuate back and forth. In the current CSD scheme, Firmware can be used to reduce or eliminate static interference.
CapSense Plus
CapSense Plus means that in addition to CapSense, PSoC can perform many other functions such as: LED driver, SPI M/S, I 2 CM/S, LCD backlight, motor control, temperature control, water level control, power management, speaker / beep Control, charger, pressure/current sensor, DTMF dialer and more. Among them, LCD backlight, motor control, temperature control, water level control, speaker/buzzer control are commonly used in white goods, and Figure 5 shows the simple structure of Capsense Plus:
To implement CapSense Plus, other functions of PSoC are needed in the system, such as: TX, I 2 C, PWM, ADC, LED driver, Timer, Counter, etc., while CSD, especially the 21 series, CSD itself has taken up most of the Resources: VC1, VC2, VC3; two columns (3) analog modules; three digital modules.
The problem we encountered was that there was no additional resources for other control. The solution was to use Dynamic Reconfiguration. Dynamic reconfiguration means that the same resources can be reused at different times, making resource utilization greater than 100%. Effectively save system resources. Dynamic reconfiguration can be used to complete CapSense and other functions outside of CapSense through a PSoC chip, enabling multiple configurations within PSoC to be loaded and unloaded during system operation. The following describes the use of dynamic reconfiguration
Dynamic reconfiguration implementation (using PSoC Designer)
1. Dynamic reconfiguration can be established under Device Editor: Config >> Loadable Configuration >> New or directly click on the graphical interface.
2. The Device Editor will display the various configurations. To switch configurations, just click on the desired configuration or use the drop-down menu.
3. Complete the functions to be completed for each configuration, and the rest of the work is the same as the normal design.
Dynamic reconfiguration API
You must manually add PSoCDynamic.h to main.c, the Load_Config API will load the required configuration, the Unload_Config API will uninstall without configuration, and the basic configuration will be loaded at startup.
Dynamic reconfiguration considerations
There are a few things to keep in mind when using dynamic reconfiguration. First of all, the basic configuration refers to the default or initial configuration.
1. Basic configuration changes will change all configurations
For example, if P0[0] is changed to Strong mode in the basic configuration, then P0[0] remains in Strong mode in all configurations.
2. Dynamic configuration (such as Overlay1) is equivalent to adding to the basic configuration
3. Changing a dynamic configuration does not affect other configurations
4. The basic configuration should be as initial as possible
5. Ensure that each configuration resource does not conflict
6. Some resources may need to be active all the time, especially the output
a) For example: PWMs
b) PWM interrupt may cause pulse interference (glitches)
c) If the PWM is required to work continuously, the PWM user module must be placed in the basic configuration.
7. The resources used by the user module in the basic configuration cannot be changed in other configurations, for example:
a) clock
b) pin drive mode
8. Basic and dynamic configurations cannot share the following resources
a) Row Outputs (Row Output)
b) Global Output Busses
c) Output Pins (output pins)
9. In the basic configuration, the user module is routed without affecting the dynamic configuration.
10. You can route the user module wiring in the basic configuration to the dynamic configuration at the same time, which can prevent trace conflicts.
CapSense's success stories in various home appliances
CapSense has been widely used in a variety of home appliances. Let's look at the role of PSoC in several major cases.
washing machine
Touch button; touch slider; communicate with main MCU via GPIO or I 2 C; LED drive; waterproof design.
Refrigerator / vertical air conditioner / water heater
Touch button
Electric teapot/coffee oven
In addition to touch buttons, PSoC measures and controls temperature and displays water temperature and water volume through the LCD. PSoC also controls valves and motors. These are implemented by a single PSoC. The main user modules used are CSD, Timer and ADC. .
Induction cooker
With proximity sensing, the backlight is turned on when a close-distance conductor is detected, and the menu is activated; the CapSense button can control the menu; the CapSense slider can control the fire/temperature/time, etc.; the manufacturer logo can be displayed through the LCD; .
Conclusion
Not only does PSoC support CapSense for the perfection of these features, but it also provides a platform for us to achieve the next generation of great ideas.
:
Cable and Wire,Electrical Wire ,Wire Cable ,Outdoor Electrical Wire
Cable Sleeve Co., Ltd. , http://www.nbshrinktubing.com