Cellular Phones In The Capacitance Sensing
For most of today's consumer electronics product development and improvement
, the industrial design is the core driving force. In the mid-market cellular phone row Industry, user interface improvement is the new cell phone the key to success. If a cell phone, no one is willing to use, then the No matter how good it is, what significance does it! With this in mind, manufacturers are focusing on developing innovative technologies in order to be able to replace the occupation of Buttons and switches of space taking into account the cellular telephone user interface (CPUI) performance. In the use of capacitive sensing CPUI is to reduce the total An effective use of space technology. Capacitive sensing to achieve a lower cost, robustness, flexibility and an intuitive CPUI, while the And does not undermine the existing portable equipment dimensions and function compatibility. Capacitive sensing capabilities, such as white LED driver with And battery charging, and other standard cell phone features, combined to further reduce the cost of cellular phones. Cypress CapSense used The PSoC mixed-signal array technology, enables manufacturers to easily integrate into their cellular phones capacitive sensing capabilities
A typical mid-market CPUI by a few buttons, switches and display component. If you just want to have the basic functions, CPUI only one sleeve Zhen-type alpha-numeric keypad, the display may be coupled with a power switch is sufficient. However, many consumers will have only a The basic functions of mobile phones are satisfied with that? If you still want to have 10 million, 200 thousand, or even 30 million, then quickly forget about the; this, but Is the only one to ask! Currently, manufacturers design phones that can browse the web, send text messages, take pictures, and even storage and broadcast Play music. In the consumer market, these features are a key factor to attract most consumers. To support these features, the manufacturer The need to increase CPUI function. For CPUI, the function of the increase will have two consequences: either the size of larger, or the increasingly complex Miscellaneous. Unfortunately, yes: consumers but also for a more simple and compact cellular phone soft spot. Consumers will no longer mention the size of the bricks Cell phone walking around all the! Cellular phone manufacturers how to address consumers of this dilemma? One possible alternative is to use Capacitive sensors are used to replace the traditional buttons and switches. Capacitive sensor can easily replace the digital switches and linear sliders, the two Who exactly is the existing CPUI the most commonly used parts.
The basic form of capacitive sensors is that a pair of adjacent plates. Shown in Figure 1, in which adjacent inherent capacitance between the plates. The capacitance and the thickness of the plate is proportional to, but not with the distance between the plates is inversely proportional to. Under ideal circumstances, this will be the only sensor Measuring capacitance. When a conductor (such as: finger) placed near the place where the two plates, and this will increase the intrinsic capacitance, and a
United capacitor. At this point, measurable capacitance that is inherent to the sensor capacitance and coupling capacitance of a finger, and. When the finger on the capacitive sensor Over time, capacitance will increase. Removed the fingers, the capacitance will be reduced. With the addition of intelligence used to measure the capacitance change after, you can In order to determine the presence or absence of a finger.
Capacitive sensors commonly used electronic circuit printed circuit board (PCB) implementation method used in two close to each other, a limited interval of copper pad or printed Thread. This is a basic capacitive digital switch. Similarly, the linear slider from the PCB on a capacitive sensor array group Sing. Typically, the sensor is a copper plate grounded, leaving only one active plate. In fact, the interconnect capacitance will pass the side To increase the intrinsic capacitance sensor and generates a
total 10pF ~ 30pF typical. A typical finger coupling capacitance values 1pF ~ 2pF. Achieve
The problem is that capacitive sensors designed to measure a finger caused by a 3% capacitance change in the circuit.
Relaxation oscillator is an effective and simple capacitance measurement circuit. A typical relaxation oscillator circuit topology shown in Figure 2. The circuit pack Including four components, namely: a synchronous comparator, current source, discharge switch, and capacitive sensors.
The beginning, discharge switch in the open state, the current source of capacitive sensors linear charge. Capacitive voltage sensor positive Ramp-up until over until the comparator threshold. Comparing the output from low to high conversion. This will result in discharge switch is closed,
Together. Capacitive sensor through the low impedance path to quickly discharge to ground. The process will compare the output of the transformation from high to low, Then repeat this cycle. Output frequency (fout) depends on the charging current and capacitive sensor values, the relation is as follows:
A typical design will set the oscillator frequency of 20kHz to 200kHz range. Then, the frequency fed into an intelligent measurement circuit. By measuring the frequency changes, you can determine whether there is a finger. It is widely used in relaxation oscillator Frequency Measurement There are two ways, a way to measure the frequency; another way to measure the cycle.
Frequency measurement need to adopt a gated timer to measure for a given period of time of the relaxation oscillator frequency. Specifically shown in Figure 3. Right Timer to read in order to determine a fixed cycle, the cumulative counts. This method is applicable to low-frequency occasions, this time, and oscillation Device cycle, compared to capacitive sensor discharge time can be negligible.
Cycle, as measured by the oscillator frequency pulse-width modulator (PWM) gating signals, as shown in Figure 4. Than the relaxation oscillator using a A higher frequency of the frequency of the timer for timing. Timer clock faster, the higher the resolution of capacitance measurements. The above two methods can be Using the traditional 555 timers or more complex micro-controller to easily. As the finger to determine the presence or absence of the need to draw intelligent soft -Pieces of algorithms, therefore, micro-controller-based solution seems to be more delicate.
Cypress's PSoC mixed-signal array and the CY8C24794 series CY8C21x34 using CapSense technology; and have a A unique group of hardware components used by relaxation oscillator topology to achieve economic, simple design of capacitive sensing. Figure 5 shows the This topology. The component groups include: multiple precision timers and counters, a discharge switch can be automatically connected to the comparator, A programmable current source, as well as an enable pin is a potential for each of the capacitive sensors universal analog multiplexer. And the Some PSoC as to achieve an application-specific peripherals are required to configure the internal registers. PSoC applications in the design of Provide assistance to PSoC Designer is a software tool, including a dedicated user module and guide for the set up for the capacitive sensing Meter to configure the internal registers. This powerful combination of engineers to provide the realization of a simple capacitive digital switches (and even more Plus the complex capacitive linear slider) the tools they need. In addition to internal configuration registers in addition, PSoC Designer also includes the necessary software Pieces of routines used to determine whether the number of switches on the touch of a finger or a finger on the precise linear position of the slider. In order to realize a complete
Capacitive sensing applications, and finally necessary to increase this intelligence.
The intelligent software algorithms provides two functions. The first function is to receive from the measuring circuit is converted to a finger count test results. Digital switches and linear sliders require this feature. The second is through a multi-sensor array capacitance to calculate the weighted average hand Means the location on the linear slider. A two-symbol has an inherent single slider Symbol LSB. If the finger on the slider, then it can be To 1 yuan in the yards and / or code yuan 0. However, the finger position detection resolution often requires more than the actual individual capacitive sensors inter - Distance, therefore, the second features the use of an interpolation algorithm. LSB interpolation processing will be reduced from a yard yuan to 1 / 2 yards yuan, 1 / 4 yards yuan Or 1 / 16 yards yuan. Interpolation is to achieve a stable capacitive linear slider key. CapSense technology and intelligent combination of software algorithms to enable Was PSoC capacitive sensing applications become a leader in the field.
Capacitive digital switches can easily replace the current CPUI the basic alpha-numeric keypad and power switch. This alternative The advantages are twofold: CPUI the physical depth and the total cost are to be reduced. The use of capacitive sensing, a number of complex and basic CPUI Functions can be integrated into a capacitive linear slider. Slider available for web browsing or traversing the scroll off the address book function, Volume control, and even brightness control function. The realization of all these functions is less than the space occupied by the traditional CPUI
A need to address the problem is with the surrounding environment of isolation. If you allow your fingers in direct contact capacitive sensor, or capacitive sensing Device exposed to the other under the external damage, cellular telephone service life will be shortened. Therefore, the need to use some kind of isolation material to electricity Capacitive sensor and separated from the surrounding environment. Portable computer and media manufacturers often use polyester tape or plastic film to provide the necessary Isolation. Unfortunately, the isolated use of materials led to the coupling between the finger and the sensor capacitance smaller. Coupling capacitor means reduced hand Refers to the decline in detection sensitivity. Common isolation material thickness of 20 mil (mil). Maximum thickness value is close to 2mm. If more than the Thickness, the capacitive sensitivity of the sensor will be impossible to detect a finger down to the point of existence. Although the use of isolation layer will cause the total
Body of the decline in sensitivity, but it for the cell phone manufacturers to provide access to creative way. Manufacturers can hide the two-dimensional sensor
A variety of colors of the plastic film behind. Imagine such a plastic film, in its surface printed using screen printing method may be formulated For basic cell phone features an alphanumeric patterns. Further use in the screen printing method along the plastic film surrounding print a scroll bar, so that we can To achieve advanced features. The same capacitive touch pad, plus a variety of plastic film is equivalent to a number of CPUI function. Let us recall a Mentioned in this article at the beginning of the next cell phone consumers of problems. Consumers are demanding CPUI be able to handle more and more capabilities while shrinking The small size of its own. With touch pads, cell phone manufacturers, is another difficult to find a solution. Touchpad solution for the workers
Engineers provides the flexibility for manufacturers to provide a greater product consistency, and to make consumers fascinated.
Capacitive sensing functionality with other features of the standard cellular phone, combined to reduce mobile phone costs. Using CapSense technology, PSoC mixed-signal arrays is to provide this flexibility and design. PSoC can be driven embedded in mobile phone display white light inside the LED, and even cellular phones can also be an internal battery. In the past have been by a separate microcontroller to handle the functions now can be set Into a single PSoC in the For today's mid-market cell phone manufacturers, capacitance sensing is a thing as advantage. Capacitive sensing CPUI has not only improved Mobile phone industrial design, but it also provides for expanding consumer demand for innovative solutions. Cypress uses CapSense technology, PSoC mixed-signal arrays to achieve high performance and cost-effective solution for capacitive sensing of the key .
by: Andrew Page
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