Feature Medical Technology
individual channels may additional capacitors be needed. The chips are available as QFN or SSOP packages and with different numbers of chan- nels (FMA1127: nine or twelve chan- nels; FMA1125: six or eight channels, which can also be configured as I/O pins). These are ideal for those who design very compact devices. One highly practical feature for designers is that the I/O pins are pro- grammable from the host for various functions, either as GPIO, direct output signal when buttons are pressed or as an external interrupt. The FMA1125 can even drive LEDs on up to eight pins: an integrated PWM provides appropriate dimming (six-bit accuracy). The I/O pins can each be loaded with up to 16 mA, which means that LEDs can be con- nected directly. For communication with the microcontroller, an I2
C inter-
face and additional interrupt signals are available (see figure 1 below) Thanks to patented technology from the Korean company ATLabs, both modules recognise touch digitally: they
Owing to the high sensitivity of the modules, the touch screen can even be operated whilst wearing gloves, which is not necessarily the case with capaci- tive screens. In medicine, disposable gloves are often required, but it is equally important that the equipment can still be operated.
Multi-touch made easy
In practice, devices are seldom equipped with only one button - they generally have keypads with a number of closely spaced sensor surfaces. Here it is important to distinguish between intended input and accidental contact. The chip only processes signals that exceed a certain threshold - but what if this happens at several buttons? The FMA1127 and FMA1125 have several functions that address this problem (APIS: Adjacent Pattern Interference Suppression).
In the simplest case, the only button that responds is the one with the high- est impedance. If the input design specifies that every finger touch is processed, however, this is where the
Figure 1: The host microcontroller controls and configures the FMA1127 touch screen controller using the I2
C bus
Figure 2a: This slider is implemented with two transparent electrodes. This is an easy way of turning a standard LCD display into the input device
tribute to reliable operation, even with a high level of crosstalk due to factors such as humidity. Since the TSC also reports not only the status of individ- ual input channels but also the raw sensor data (without calibration etc.), customised functions such as special filtering algorithms, sliders and so on can be implemented very easily (see figure 2 a & b).
The sensitivity of each sensory channel can be adjusted independ- ently, making for considerable flexibil- ity in touchpad design.
compare the sensor input impedances with integrated reference impedance (shown in figure 1) and are therefore highly immune to interference. Configurable AIC (Automatic Impedance Calibration) adapts the chip to changing environmental con- ditions, enabling the sensitivity of each sensor to be kept constant. Heat, moisture or manufacturing tolerances are no longer a problem, and the touch sensors always function reliably.
APIS 2 comes in: here, any value that exceeds the threshold is a valid input. In the example, three buttons are active. APIS 3 incorporates a combina- tion of both techniques: it responds to a maximum of two keystrokes - ideal for a shift function, for example. Because all this filtering is done in hardware, the burden on the host application is correspondingly lower. Together with the high sensor sensitiv- ity of 0.078 pF, these functions con-
Figure 2b: The FMA1127 features a slider, four individual buttons and six LEDs
Economical and flexible Manufactured with standard CMOS technology, the device has an operat- ing power consumption of only 140 µA; standby power consumption may be as little as 0.1 µA. This makes the module an ideal choice for mobile device applications.
Bluetooth low energy heart-rate belt
so called ‘world's first’ production-ready Bluetooth low energy heart-rate chest belt has been announced by Nordic Semiconductor ASA in conjunction with Dayton Industrial Co. Ltd. This product enables anyone with a smartphone that has the latest version 4.0 of Bluetooth to be able to set-up and use a wire- less heart-rate (HR) belt within seconds and so spur the development of a whole new range of Bluetooth low energy-based health and fitness apps. This could include new ways of collecting, interpreting, and displaying HR training data – including motivational social media-based data and progress sharing. The nRF8001's ULP performance and size enables the Bluetooth low energy heart-rate belt to run for up to 1.5 years from a CR2032 coin cell under typical usage conditions (1-hour per day). It is 1.1cm thick and is compact at 3.8 x 6.5 cm. Nordic Semiconductor
A
www.nordicsemi.com Electronics JULY 2011 Enter 217
The module is even more economical: it only uses 100 µA in operation. Thanks to the integrated reference impedances, the sensor needs no external components. And an external voltage regulator is not required if the internal LDO is used for the power supply of the chip.
Designers of medical devices there- fore have every reason to make touch sensor controllers their technology of choice: the cost of circuit design and software adaptation is minimal, and the reward is a device with no mechanical switches, buttons or con- trols, which is very easy to clean and offers housing designers a high degree of flexibility. Fujitsu Semiconductor
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http://emea.fujitsu.com/semiconductor 23
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