Design Tip

Six Tips on Touch Input for Medical Device Designers

With their growing electronics content, medical devices have become sophisticated, interactive products, yet their increasing use in the home environment requires that they be simple to use. A touch input HMI (Human-Machine Interface) is a user-friendly way to accomplish this, and a Resistive-type touch panel is the most common solution. These devices can monitor and transmit vital signs (e.g.: pulse or a blood pressure reading) to a medical facility, or allow the user to download their information at home. For the medical device designer, here are six touch panel integration tips for successful home environment product design:

1. Evaluate the end-user operating environment, application dynamics, and optical and electrical performance needs. These are all critical areas when selecting and designing-in the right touch panel solution. Remember that the patient and minimally trained family members, rather than medical professionals, will primarily be operating the device. Ambient lighting may be much lower than a hospital’s, and the home electrical environment is quite diverse and uncontrolled.
2. Ensure that the touch panel’s top film is resistant to typical home cleaners, such as disinfectants and bleach. Although infection control and sanitation are necessary, home cleaning agents differ from typical hospital cleaning solutions, and lab tests should be conducted with your specific materials to prolong the life of the touch panel and medical device. Adding anti-smudge coatings to the touch panel can also repel oily fingerprints and improve ease of cleaning to greatly improve LCD visibility.
3. Enclosure design is important. The touch panel needs to be properly sealed to the top panel to prevent liquids and other fluids from seeping inside the device and causing damage to components or circuitry.
4. Consider the touch panel’s material properties for impact resistance. Everyday household objects – from a pen to a letter opener – as well as normal finger touches of various force, may be used to enter information on the touch panel and potentially cause damage. Users with impaired aural or sight impairments need clear response acknowledgment to touch inputs. One method is to use large targets that change color and simultaneously issue audible beeps and sometimes a haptic indication as well. There are also cover films available that provide more scratch-resistant top surfaces than usual touch panels.
5. Ruggedize the touch interface. In the home environment, the device will most likely be moved around, bumped into by an errant pet or child, banged into furniture and possibly even dropped. Creating a strong surrounding for the display assembly will offer the best chance for being subjected to various impact types.
6. If the medical device uses wireless transmission, radiated interference can be both internal and external, because the touch panel can be a receiving and/or a transmitting antenna. Home computers, cell phones, interactive gaming systems, and microwave oven emissions can affect product performance, and may require a shielding or structure adjustment to remedy. LCDs can also have high-speed, fast transient signals that couple to the touch panel. In this situation, such signals can look like noise to the touch panel, as it is essentially a low signal level analog device, so be sure to test your breadboard and prototype carefully. If changes are warranted your suppliers should be consulted if you need assistance.

Using these basic tips as starting points will help establish fundamental design requirements for touch panel integration in the new – and growing – market of home medical devices.