In this video, we talk about the ubiquitous seven segment display and how you can use multicolor LEDs to provide the user with more information than just a simple readout.
Seven segment displays are still the most common display technology in many applications in both consumer and industrial applications. For example, they’re used in factory automation to indicate parameters to the operator, such as temperature, and oftentimes a single display will be used to show multiple parameters.
For this video, we have a multicolor LED from ROHM, which uses their PICOLED mounting to place two LEDs in a compact package, and makes it easier to display multiple pieces of information on a single display.
Combining LED Colors for Usability
As you can see in the video, we have two sets of LEDs and we can light those up at yellow/green, red—or, if we turn both on at the same time, we get an orange color. They're a standard 1.6 X 0.8 package, and they're .5 millimeters thick. So they will fit inside the standard light guide. You can do multi-color displays without multi-color LEDs, you just need two LEDs and you need a non-standard light guide, and that's going to add additional PCB space and additional cost for the special light guide.
You could use red, maybe for temperature readings, and yellow-green for your time remaining on a process. Or maybe you have a temperature reading that needs to be within a certain range. To easily indicate where your temperature is at in that range to your operator, you can have it be yellow-green for the standard range, its normal operating conditions. You can have orange, for a warning range, or you can just go to red if it's outside that range.
This allows quick access to important information. When the operator sees the display, they don't need to know exactly what the number is—they get an immediate indication of whether that value is in its normal operating range or not. So these multi-colored LEDs give you more information than just the data being displayed on them.
LED Packaging Concerns and Solutions
Besides placing the two LEDs in a compact package, ROHM has also done a couple of things that help improve the reliability of the advice. With your typical LED with electrodes on the end, it's possible for solder to wick up into the package and cause the LED to fail or discolor. What ROHM has done is place the electrode on the bottom side and then placed a layer of resist on the top side. This prevents solder from penetrating the package and causing the LED to fail. Now the backside electrode also allows you to have a smaller pitch and higher density placement so you can do things like dot-matrix displays with these LEDs.
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