This is nothing new - I have seem numerous designs of big segment displays that incorporate large arrays of parallel LEDs to serve as each segment, but using so many LEDs is such a waste! Not only do you have to use a lot of LEDs, it can take quite a bit of current to light up that many LEDs at a time.
For these reasons, I decided to come up with a way to diffuse the light from one or two LEDs over a large thin area to serve as each segment. This would reduce the need for so many LEDs and also reduce the total current consumption.
The reason the LEDs appear to flash in the video is because the camera has a faster capture rate than the human eye. The LEDs are flashing on and off - that is how the multiplexed control works, but the naked human eye cannot see it because the pulse is too fast - around 100Hz.
My final display uses 54 LEDs to form three 4" x 2.5" digits with a colon to separate the minutes and seconds. Each digit in multiplexed, so they share the control lines. The total current through each segment is 6mA, but because each digit is only on 1/3 of the time and each segment is comprised of two parallel LEDS, this equates to about 1mA per illuminated LED at any given moment. More current could certainly be used, but my LEDs are controlled by a low current sourcing register. If more current is provided, then display could be much larger than the one I created.
Step 1: Required Materials
Foam Board - As with most all of my LED array projects, I like to use crafting foam board as the base instead of a solderable perf board or PCB. The primary reason for this is cost. A full sheet of foam board can be found at many dollar stores or at any craft store.
LEDs - This design uses 2 LEDs per segment, so 14 per digit plus 2 for the colon (dot). Pretty much any color can be used. More on the selection will be discussed in Step 2 - Picking Out LEDs.
Black Paint - This isn't necesary, especially if you get black foam board, but I like the look of the black background behind the LEDs.
Wire - You will need at least a few feet, depending upon how long of leads you need. The wire gauge for the power lines should be just big enough to handle a half of an amp max, so 25 gauge or bigger wire is good. Some lengths of a much smaller gauge would be fine for connecting LEDs together in strings.
Sheer Black Pantyhose - For filtering the display output (see Step 10)
Sharp Pick - I use a dental pick, but an ice pick would also work; it just needs to be thin and sharp.
Hot Glue Gun - Hot Glue works very well to dissipate LED light. It's also a great way to protect and insulate the soldered leads.
Helping Hands - Not entirely necessary, but definitely very helpful.
Needle Nose Pliers
Soldering Iron and Solder
Classroom Glue Stick