We were working on a
treadmill product that has the functionality of running the mill speed, incline
/ decline the mill position (it has few more advance features, but relative to
this story). It is a software that is running on the touchscreen display that
has windows 7 embedded operating system. All the buttons and
everything is on the screen and it responds to user's touch. We were in the
process of choosing touchscreen display that suits on our treadmill. So
different people were doing looking/ testing from different angle. Industrial
designer more emphasizing on the look and feel, whether it meets
industry standard etc. Mechanical designer looking the display whether that
will mount on the treadmill perfectly or not. Whether the mount will hold
the display on the treadmill when people will be jumping/running on it fast
etc. I'm not an expert on those fields so, i'm skipping the details of their
process.
Now
for my part. First thing I had to check whether it meets the optimum
configuration with the hardware. Once the hardware meet that requirement, then
checked the basic functionality. Then then the important thing is the
Performance/Response. Think about it, its a treadmill firm/software. Speed
button touch will increase/decrease the speed, stop button touch will stop the
mill and so on. For extreme circumstances, when you hit the STOP button,
you expect the mill will stop. Similarly when you touch decrease button it will
reduce the speed. These functionalities sounds very basic, but if it
is used by some patients for Rehab or elderly person, it may become a BIG
issue. It's like a car, no matter what situation you would expect that break
will stop the car. If the response of the touch is too low or too sensitive
then we will have problems as well.
Touch
screen displays are usually of two kinds- Resistive and Capacitive.
"Resistive
touchscreen comprises of several layers, out of which the flexible plastic and
glass layers are two important electrically resistive layers. The front surface
of resistive touchscreen panel is a scratch-resistant plastic with coating of a
conductive material (mostly Indium Tin Oxide, ITO), printed underside. The
second important layer is either made of glass or hard plastic and is also
coated with ITO. Both the layers face each other and are separated with a
thin gap in between. An electrical resistance is created between both the
layers in such a way that charge runs from top to bottom in one layer and
side-to-side in another." [1]
"Capacitive touchscreen also consists of two
spaced layers of glass, which are coated with conductor such as Indium Tin
Oxide (ITO). Human body is an electrical charge conductor. When a finger
touches the glass of the capacitive surface, it changes the local electrostatic
field. The system continuously monitors the movement of each tiny capacitor to
find out the exact area where the finger had touched the screen." [1]
Both
has advantages and disadvantages. Capacitive is highly touch sensitive and doesn't need a stylus and supports multi-touch. Resistive is high resistance to
dust and water, low cost. Which type of touch screen to choose? It depends on
where, how its going to be used, what are the purposes etc.
For our case, as we were going to use it on rehab treadmill. As test basis we used the Capacitive touch screen which has lot more advantages. Capacitive touch screen looked and felt good in terms of look and feel. But it failed in one interesting area - sweat! (Basic science - Salt water is a good conductive media.).
For our case, as we were going to use it on rehab treadmill. As test basis we used the Capacitive touch screen which has lot more advantages. Capacitive touch screen looked and felt good in terms of look and feel. But it failed in one interesting area - sweat! (Basic science - Salt water is a good conductive media.).
We put
some salt water on the display where we have buttons layed out. We saw that it
was generating a touch on the button. And the worst case we saw it, when we put
the salt water on the speed button, it was ramping up to the highest speed
within few seconds. Imagine what would it do to the person on the mill, and
what if it was a patient who will be doing a rehab. So, there ends the story of beautiful capacitive display for treadmill (until they fixed this issue). On the other hand despite of other limitations of Resistive touchscreen display, we are going back to resistive one.
My intention was not to discuss about how to test touch screen display in general. Rather its about how to test products in practical way that actually can happen to end users based on the nature of the product. As it was going to be used on a product that will be used by patient, patients safety comes first before starting any other type testing. Testing is very important. Testing from practical scenario is very important. It may save lives.
My intention was not to discuss about how to test touch screen display in general. Rather its about how to test products in practical way that actually can happen to end users based on the nature of the product. As it was going to be used on a product that will be used by patient, patients safety comes first before starting any other type testing. Testing is very important. Testing from practical scenario is very important. It may save lives.
Source: [1] Resistive vs Capacitive Touchscreen
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