PSoC capacitive touch sensor technology

Cypress PSoC is determined by the introduction of semiconductor companies have a digital and analog hybrid processing capacity of programmable SOC chips, certain series of PSoC (such as the CY8C21X34 series), due to its interior is equipped with special resources so that it can easily achieve the capacitive touch sensing function, you only need a small amount of several external discrete components that can be a common I/O are configured for capacitive sensing inputs. Capacitive touch sensing principle as shown in Figure 1, the Board of two adjacent copper inherent in the existence of a parasitic capacitance Cp, when the finger (or other conductor) near, fingers and between two pieces of copper and produce new capacitors, these capacitors amounted to a parallel to the original Cp, when we get a piece of copper connect to analog I/O on PSoC, another connection to the ground, you can change by measuring the capacitance to determine the existence of the fingers. We connect to the PSoC on copper called capacitive sensors (Capacitive Sensor), capacitive sensor on the need to cover insulation materials (shell). By internal build circuit PSoC with built-in 8-bit processor program to control the operation of the circuit, you can attach a capacitance change into count value change, which in turn translates into key actions needed switch quantity.

PSoC internal several pre-designed capacitance sensing user module, the user module can be viewed as hardware configuration and software libraries (API) set, users need to do is in the PSoC development environment (PSoC designer) user module configuration to a digital/analog array, the development environment automatically generates hardware registers configuration and library functions, and the rest of the work is some user module parameter adjustments, and the application code is written.

The entire development process is very intuitive and smooth for embedded system development engineers, will soon be handy.

Capacitive-sensing technology for industrial design provides new ideas with capacitive-sensing technology, industrial designers first can think of is to traditional mechanical press with capacitive sensor switch.

This increases the flexibility of the industrial design, because the capacitive switches can be hidden in a piece of the complete surface below, do not need to press the key that needs to be reserved for mechanical machinery parts movement in space. In some portable devices, designers hope to product gives natural spirituality, such as shell-like MP3 player, like a pebble-like handset, use capacitive switches replace mechanical press can maximize the idea of restoring the designers, product appearance has integrated effects. The key is a capacitive sensor technology, the most common way of application, use PSoC built-in 8-bit processor, you can achieve the product more user-friendly operation, such as slide bar (one-dimensional) and the touchpad (two-dimensional). Multiple capacitive sensor and emissions together can achieve slider (slider), as shown in Figure 2, PSoC sequential sense each sensor capacitance change, currently being sensing sensor, other sensors in the PSoC internally to the ground, this ensures that each sensor capacitance consistency.

Slide bar in the layout required assurance finger can also overwrite or close to at least two sensors, so that in the figure 2 count value curve will render a raised-trends, by interpolation algorithm can accurately calculate the current position of the center of the finger, the resolution of this location is much larger than the actual number of sensors.

The location of the fingers sliding direction and displacement that can be translated into the user's input.

Change the slide bar to arrange shapes can make the slide bar to render a variety of lines and beautify the appearance of the product.

Figure 3 is a kind of circle slider sensor arrangement. According to the needs of the industrial design, the slider can also look through the fan-shaped, oval, wave, and so on. Slide bar not only provides a new UI input mode, product appearance increases the necessary design aesthetics embellishment, the more mysterious. Two-dimensional slide bar constitutes the touch panel, as shown in Figure 4, by horizontal and vertical scan can locate respectively touch point of two-dimensional coordinates, laptop Trackpad is the use of this principle. With the display screen (LCD) increasing the resolution of a greater need for two-dimensional coordinate information to locate the position on the screen, the touch panel, and will have a place.

Make the best use of limited entry area with the development of portable devices, in the limited space on the product display as many input element becomes a new challenge.

PSoC soft function keys defined for this demand provides a good solution. Figure 3 shows the soft function keys for basic principles, in the slide bar or the touch panel to define a coordinate of the region, when fingers in this region in a certain time, that is the area of the corresponding function key is pressed. Soft function keys of design to design saves space on a slider or the touch panel, you can implement different types of input elements, as shown in Figure 5, 5a of this piece of touch panel, by overriding different prompting pattern 5b, 5c or 5d, can simultaneously achieve key and touch panel functionality, user input with intent can finger movement of automatic recognition by the PSoC software, no mechanical switching. This design, improve space utilization, but also as designer provides a more imaginary space.

Designers may ask, in Figure 5, 5b, 5c and 5d so different input function, can not be in this one area at the same time achieve? the answer is Yes, is the touch panel 5a into transparent metallic materials (such as ITO, indium tin oxide), will this transparent touch panel display with dynamic fitting function display (LCD), the display shows

Different button layout, you can achieve dynamic input key features. ITO the metal material transparency and self impedance proportional, that is, the higher the impedance greater transparency, use PSoC latest touch-sensing algorithm, you can make the capacitive touch sensor from the effects of high impedance, thereby ensuring that displays the results.

How to contact the user-generated interactive traditional mechanical press has used the hearts of the people, mechanical press gives the mechanical touch feedback is not available, this could not help worrying touch of interactivity.

In fact, this worry is not necessary, PSoC provides users with the other chooses. PSoC internal has plenty of digital and analog resources, capacitive touch sensing only to a part, the remaining resources can be used to further increase the functionality of the system design and optimization of the system. As shown in Figure 6, used to connect different PSoC device peripherals, you can provide the user with auditory feedback (buzzer), tactile feedback (motor) or Visual (LED) feedback and promote these peripherals can be used to implement the PSoC internal resources, without or only need a small amount of discrete components.

The resources are not enough, you can even take advantage of dynamic reconfigurable PSoC, time-of-use PSoC internal hardware resources to achieve maximum resource utilization.

Let the master product Association welcomes the capacitive touch sensing there is another application that is close to the induction, that is, users do not need to touch the product's enclosure, as long as close to a product that could be sensitive to.

PSoC near type induction is by reducing the intrinsic capacitance on the sensor to relative zoom Cp alien capacitance change, thus within the scope of induction 10cm close to human body. This near-induction as well as products of industrial design offers a new way of thinking. For example, when users are close to the product, the product of the display backlight (or effect light) is lit, so the user can see the current work in advance; or products play a piece of music, let users create the feeling of being welcome. This design has two advantages, above all, saving, as we all know, the product is used on the screen, and when large power users are not close to, full of information on the display is not functioning, so you can turn off the display appears, or backlight turns off, and when the user is near, and this can open to a large extent, save power; secondly close type induction design can increase the interactive fun, enhance the added value of products, thereby stimulating the desire of the customer.

Due to the PSoC hardware and software programmable features, as well as its rich resources on chip, making its capacitive touch sensing technology is uniquely positioned to enable product design in function and performance differences, and to the maximum extent, lower system costs.