7-segment LEDs are available in red, green, yellow and blue (maybe even in white?). There don’t seem to be any in RGB though, so if you want to dynamically use different colors in your project you either have to use multiple devices or use a different technology.
So this seemed like an opportunity for a nice DIY project: Why not take an existing 7-segment display, remove the original LEDs and add some RGB ones?
I started with an old SL-1119 display and ordered some SMD-RGB-LEDs from a seller on ebay. The LEDs came with magnet wires soldered, which came in handy, as the LEDs are as small as 1.6mm x 1.2mm.
Step 1: Remove what’s in the way
Using my Dremel tool it was a matter of a few minutes to completly remove the back of the display, including the original LEDs and contacts. Afterwards I sanded the display in order to have a flat basis for the new LEDs.
When light shines through the display body, one still can see what’s left from the original LEDs.
Step 2: Attach RGB-LEDs
For attaching the new LEDs, I took transparent two-component adhesive with low assembly time. It is important to place the LEDs accurately, so I was not able to attach more than two or three of them at once.
Step 3: Attach socket pins
32 wires (8 LEDs with one common anode and three cathode wires each) are not easy to handle, so I decided to add some kind of socket.
I am pretty happy with the result:
One thing I could have done better though, is the optical isolation of the segments. As you can see from the behind, the light from each segment spreads to its neighbors. So when a segment is not lit, you can still see a bit of the light from the other segments shining through.
Now that the display is finished, what is left to do is to connect it to some kind of driver circuit. I am not yet sure how to handle the 24 lines. Implementing a I2C driver circuit would be nice, so I could control the display from a PIC microcontroller for example.