Feature Medical Technology
ygiene is the primary concern in medicine. The easier it is to clean a device, the better: so the cards are stacked against mechanical switches, buttons and knobs. Modern devices use capacitive touch controls, allowing for much improved design. They still function even with moisture or water droplets on the screen. Touch screens are 'in': MP3 players and mobile phones have brought touch- sensitive displays into fashion and rev- olutionised user interfaces. Even in the industrial environment and in white goods, users want to use touch screens like those they are familiar with from iPhones, Android and so on. Not only do they get all the graphi- cal bells and whistles, but capacitive controls are also a real alternative to conventional mechanical switches, buttons, sliders and knobs. In addition to pure design aspects, there are real technical advantages: they don't wear out and there are no mechanical com- ponents involved.
This means that it is quite simple to manufacture systems or control panels that are completely sealed, without the need for things like buttons with expensive waterproof gaskets. It avoids edges that collect dust and dirt, and simplifies the mechanical design, which is particularly important in medical technology, since flat, smooth surfaces are much easier to clean and more hygienic.
Electronic design Engineers, there- fore need to be familiar with modern capacitive touch screens, and incorpo- rate them in their product designs.
A touch of clean technology H
Christian Harders, Industrial Applications Engineer at Fujitsu Semiconductor Europe, explores how medical devices controlled by touch are aiding a more clinically clean environment in the medical field
Selecting an appropriate sensor The sensor type and control method chosen will depend on the applica- tion. A full-size touch screen with multi-touch and gesture recognition provides maximum flexibility in the design of the application.
But the technical complexity associ- ated with such a screen may not be necessary - it is often possible to implement an intuitive operating con- cept more easily, cheaply and perhaps more compactly.
Depending on the application, it may be reasonable to assign a specific function to certain areas of the control panel, even if this is in front of a screen. It is often enough to have a few buttons, sliders or knobs, which are in the same locations on the screen. Taking this approach significantly reduces the number of touch channels that are needed. It can also simplify the layout of the sensor surfaces con- siderably, since instead of a two-lay-
New MCUs with enhanced Real-Time A
Modern capacitive touch screens are becoming the standard for HMI and are being adapted to suit hygiene critical applications such as medical
ered matrix structure, a single elec- trode layer can be used. This is much less expensive to manufacture, for example by applying transparent elec- trodes directly onto the glass. Many applications that now use individual buttons or membrane key- pads (such as blood pressure measur- ing devices) can be very easily re-designed to use capacitive controls: as part of a facelift, the operating prin- ciple can be retained, and only the technology of the controls and the design of the housing need really to be changed in this case.
The improvements listed here can easily be integrated in various applica- tions with either of the two TSCs (Touch Sensor Controllers) available from Fujitsu Semiconductor Europe (FMA1127 and FMA1125). With the functionality built into the hardware, the burden on the host microcontroller is minimal.
This means that unlike software- only approaches, there are no resource conflicts between the measurements necessary for touch operation and the calibration/filtering algorithms as well as other application functions. The TSC carries out all time-critical functions automatically in hardware, with a minimum response time of only 0.2 milliseconds. Even if the chip can respond very rapidly, this is not always desirable: rapid changes in the signal suggest an unintentional touch. The TSC can therefore be made to ignore brief signals - this prevents accidental activation and increases operational reliability.
new family of 16-bit MCUs has been added by Renesas Electronics to its RL78 micro- controller (MCU) range. The new RL78/G14 group of MCUs is ideal for a number of ap- plications, including household appliances, healthcare devices, office equipment and industrial automation systems, as well as medical and consumer products such as motor control, security systems and mobile devices. The family contributes to lower overall sys- tem power consumption and reduced development cost. The new MCUs incorporate ad- vanced on-chip peripheral functions from the company’s R8C family, meeting the needs of customers wishing to utilise existing software resources originally developed for the R8C family. The new MCUs are available in Flash ROM capacities ranging from 16 KB to 256 KB and RAM capacities from 2.5 KB to 24 KB Renesas Electronics Europe
www.renesas.eu 22 Enter 216
It is clear that the device must not generate electromagnetic pollution or interference. This can be a significant issue with touch sensors, since touch detection is mediated by a measure- ment signal: to ascertain the imped- ance of the pad, the modules evaluate the delay of the measurement pulse. Because the sensor is a branch of an RC circuit, the delay alters as the impedance changes. The measuring signal of the FMA1127 and FMA1125 is clocked at only 20 kHz. At this low frequency and with the low signal strengths, there is no significant radia- tion from the sensor surface. The two TSCs need no additional components at the touch inputs. In most cases, it is sufficient to connect the sensor surfaces with the pin - this saves space and decreases the BoM. Only with large differences in con- ductor length and/or sensor area of the
JULY 2011 Electronics
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