You could get this down to 11 pins.

Unfortunately I can not: The red, green and blue anodes for each segment are already connected on the tiny SMD-LED chips. So if I want to use multiplexing, I can only do segment multiplexing, e.g. by connecting a+e b+f c+g d+dp and separating anodes a+b+c+d from e+f+g+dp. So I would end up with 14 connections (2 anode + 4 segment cathodes per color).

8 for the element common (ground?)

tie r, g, b common together (vcc?).

then have your microcontroller cycle through the red, green, and blue pins (either tying them to ground/high state or making them floating), and cycle through selecting the 8 elements.

By doing this quickly enough you can have persistence of vision such that the number 8 could have all different colors for each segment still, and you could even still do pulse width modulation by changing the on/off ratio for r/g/b in each element.

There are already displays that are not just led matrix displays which require this sort of “scanning.” A popular one is the 10 segment red/green bar graph. It has 10 ground pins, and 1 green vcc and 1 red vcc. In order to not show yellow everywhere, only red or green can be have vcc, right? So the way to control those is to raise vcc on green, then ground all the elements that must be lit green, or yellow, then lower vcc on green. And then in the next iteration, raise vcc on red, and ground all of the elements that must be red, or yellow. Red and green are only on for a moment, but they are persistent enough such that you can see the red, green, and the places where red and green combined to make yellow, without any flickering.

Hope that makes sense, would tell you in German if I could.

Google the words : multi color 7 segment LED
and see what you get.

For example, Genixtek has something: http://www.gtctw.com/LED_DISPLAY.html

Brett_cgb :

One way to simplify the LED-to-socket connctions would be to bring out the + from each segment from all colors (ie +a, +b, +dp) to pins (8), and tie all the – pins from each color together and bring these out to seperate pins (-R, -G, -B; 3 pins). There is a total of 11 pins required.

Problem is, that the anodes for R, G and B are already connected on the SMD chip… So if I want to use multiplexing, I can only do segment multiplexing, e.g. by connecting a+e b+f c+g d+dp and separating anodes a+b+c+d from e+f+g+dp. So I would end up with 14 connections (2 anode + 4 segment cathodes per color).

Ian :

Very pretty. Which seller did you get the pre-wired LEDs from?

I got them from the seller ‘ledbaron’ on ebay in Germany. He sells various LEDs as accessories for model railways. I don’t know if they are available anywhere else. The size of the SMD LEDs is 0605, but I don’t know the type or manufacturer.