6 Questions to Ask when Choosing your TFT
1. What Size for a New OEM Design?
Go with a standard, off the shelf size.
Standard, off-the-shelf TFTs are available in sizes ranging from less than an inch to several inches. Focus holds inventory on sizes from 1.3” to 10” since they are the most common and will be available for many years.
Off the shelf is just what its name says. Most of our standard displays are held in our Chandler, AZ location so we can ship prototype samples or lower volumes the same day you order. Larger quantities have a shorter lead-time of eight to ten weeks.
Off the shelf also means a low MOQ (Minimum Order Quantity) and no tooling fee. (NRE)
Because these are standard products, we sell the same display to several customers, resulting in a lower price for each customer.
Standard sizes include: 1.3”, 1.4”, 1.8”, 2.0”, 2.4”, 3.5”, 4.0”, 4.5”, 4.3”, 5.0”, 7.0”, 8.0”, 9.0” and 10.0”.
2. WHAT IS THE OPTIMUM RESOLUTION?
Display resolution is the number of dots on the screen. The more dots, the sharper the image. Resolution is measured by the number of dots along the ‘X’ axis and the number of dots along the ‘Y’ axis.
Is higher resolution better?
With a higher resolution, you will achieve a sharper contrast, but the display may require extra drivers necessary for the display to refresh. Depending on the amount of extra required drivers, the piece price may increase.
If you need highly detailed videos, then go with a higher resolution. If you only need to display icons, sine waves and characters, then go with a lower resolution.
3. HOW BRIGHT OF A DISPLAY DO I NEED?
The TFT’s brightness is measured in Nits. One Nit is how much light is generated by one candle.
For TFT sunlight readability a display needs a minimum of 700 Nits, although 1,000 is preferred. Something to consider if your medical product is a handheld/battery powered product, is the power consumption. If your display has a higher nit count, power consumption will be higher.
It is possible to adjust the brightness of the display depending on the environment. Direct sunlight may need a brightness of 1,000 Nits, but a hospital room in the dark may need something closer to 50 Nits. It’s bad enough in the hospital room to hear all the beeping of the machines, but no one wants to sleep next to a hear monitor that is more like a spotlight.
4. WHAT TYPE OF TOUCH PANEL?
Touch panels come in two flavors: Capacitive and Resistive.
Resistive Touch Panel (RTP) is the most common. They are simple to program and durable for heavy use or outdoor environments.
RTPs are an overlay on the LCD glass that blocks around 5% of the display’s brightness. Also, an RTP is limited to one touch at a time.
The panel is activated when something presses the top layer of the overlay and it makes contact with the bottom layer of the overlay. That means anything will activate it such as a finger, pencil eraser or a gloved hand.
Phones, tables and laptops all use Capacitive Touch Panels (CTP). They have the ability to zoom, pinch and scroll. They are more expensive and require more programming than RTPs.
Since the touch panel is part of the glass, there is no blockage of light from the TFT.
Most capacitive displays require something with an inductive load to activate it, such as skin or a stylus.
5. TRANSMISSIVE VS. TRANSFLECTIVE POLARIZER
All displays require light to be readable. The light source can be from ambient light, the display’s backlight, or a combination of both.
Transflective uses a mixture of ambient light and a backlight to illuminate the display. This makes it an excellent choice for sun light readability and nighttime operation.
Transflective is a newer technology that is more expensive than transmissive.
Transmissive requires a backlight to illuminate and blocks ambient light. This can make it brighter than Transflective, but difficult to read in direct sunlight.
Cell phones and tablets are transmissive. They are readable in the shade or dark, but difficult to read in direct sunlight.
There are two methods for making transmissive displays sunlight readable.
1. Increase the brightness
2. Adding an anti-glare film
6. WHICH INTERFACE?
The TFT’s interface connects the LCD with your medical OEM product. The two main players are SPI and HDMI
SPI (Serial Peripheral Interface):
SPI requires few I/O’s (In Outs) and interfaces with the lowest cost processors. It’s a good choice to display characters, icons and a few images, but performs poorly for high resolution video.
HDMI (High-Definition Multimedia Interface):
HDMI is fast and an ideal interface to display video. With Its plug and play feature, there is no need to reboot when connecting to your product.
Its more expensive then HDMI, but worth it for medical equipment that needs quick exchange of information.