How capacitive sensing works
So, what is the work of capacitive sensing? The diagram below shows the cross section of a capacitive sensing button. As shown, under the outer cover material, there are conductive copper block regions and conductive sensors. When the two conductive elements are in close proximity to each other, a capacitance value is generated, which is labeled Cp in this figure, and this capacitance value is formed by the coupling phenomenon between the sensor pad and the ground plate. Cp is a parasitic capacitor, typically on the order of 10pF to 300pF. When the sensor is close to the ground plane, it also forms a fringing electric field that can penetrate the outer cladding. Basically, human tissue is also an electrical conductor. When a finger is placed near the edge electric field, the conductive surface area of ​​the capacitor system is increased.
However, this additional finger capacitance value labeled CF in the figure is of the order of 0.1 pF to 10 pF. Although the presence of one finger causes a change in capacitance, the magnitude of this change is quite small compared to parasitic capacitance. The measured capacitance of the sensor is called CX. In the absence of a finger, CX is essentially equal to CP. However, when it is meant, CX is the sum of CP and CF.
Figure 1 finger capacitance value
Capacitive sensing design
After we understand how capacitive sensing works, how do you start designing a capacitive sensing interface for a particular product? We need to consider the needs of the design. Where is this product used? Is the use environment harsh? The most important factor in this design is the battery life or the durability of the product. Different factors have different effects on the design.
Depending on the type of product being designed, power consumption may or may not be a critical factor. For example, on battery-powered handheld devices, power consumption is of paramount importance. And a pair
The overall average power consumption, that is, the battery life, is controlled by setting up three different work areas. One working area is the fast response area, and each sensor in this area is scanned every 200 microseconds. The system enters this area with the button and sliding touch in continuous operation. With little or no operation, the system can enter a slow response zone and reduce the scan frequency to approximately every 100 milliseconds. Finally, if there is no operation for a long time, the system can enter deep sleep mode, saving power. By implementing an energy-saving, slow-response mode, the system can consume less than 50μA of average current when the portable handheld device scans 3 buttons every 100 seconds.
In today's electronics sector, noise is another important consideration. Various types of induced noise, such as noise from power lines, and radiated noise from mobile handsets or fluorescent lamps, are present all the time, so they must be considered. For effective prevention, our goal is to increase the signal-to-noise ratio and eliminate false touch responses.
When designing signal-to-noise ratio, durability, electrostatic discharge resistance, and accuracy, the thickness of the outer cover material and the thickness of the outer cover are greatly affected. Moreover, when considering the type and thickness of the material, a compromise must be taken in many respects depending on the needs of the product. As the thickness of the outer cover material increases, both signal and noise are reduced. However, the thicker the outer cover material, the stronger the resistance to electrostatic discharge. The human body's electrostatic voltage can be as high as 15 KV, and the outer cover of the capacitive sensing system helps to prevent permanent damage to the integrated circuit when subjected to such electrostatic discharge. Another solution is to use a layer of polyimide (Kapton) tape that works well in applications that require superior electrostatic discharge protection. Of course, the thicker the outer cover, the less likely it is to break or be destroyed.
Rocker Switch is also called warped plate Switch.The structure is the same as the button switch, but instead of the knob to the boat type.The ship type switch is commonly used as the power switch of electronic equipment, and its contacts are divided into single pole and double pole double throw, some of which have the indicator light.
Rocker Switch
Rocker Switch,Double Pole Rocker Switch,Mini Rocker Switch,Bar Rocker Switch
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