I'm planing to start a project that is a number display. It consists in 2 components:

  • The controller: a smart component that knows which number to display
  • The (single) digit: it display a single number;

I'd like to make them "chainable": [digit] + ... + [digit] + [controller].

From right to left: we start with a controller. It knows which number to display. The controller pass this information to its left side, that is a digit and the information should be send to all digits in the chain.

Please, ignore the complexity of the controller or how it knows the number to display.

Despite the title, I'm not using the 7-segments component. I'd like to 3D print a big 8-shape, and fill it with LEDs.

How should I build the digit?

I have 2 options in mind.


  1. The digit has 7 addressable RGB LEDs. In this case, the controller sends a signal to control each individual led, in each digit.

  2. The digit has 7 non-addressable RGB LEDs + a microcontroller. From right to left, the first digit receives a number (eg: 1234), displays the "4", and pass the rest to its left side. The next digit do the same, displaying the 3.


For option 1:

  1. Can the controller "auto discover" the total number of addressable RGB LEDs?
  2. Maybe, each segment needs more LEDs (2 or 3) depending on size. Meaning that each digit could be 14 or 21 LEDs. A 10 digits number would have up to 210 addressable LEDs. Is it a problem?

For option 2:

  1. Which microcontroller is recommended for this setup? It should receive an information (if possible, a string), parse it, and pass some other information.

And a last question: is there an big price difference between these options?

For this long text. But I'd like to hear from people more experienced before start.


  • \$\begingroup\$ Do you have an upper limit on how many digits you want? Do you have a target size for the digits, and hence a target number of LEDs per segment? \$\endgroup\$
    – jonathanjo
    May 10, 2020 at 10:25
  • \$\begingroup\$ 10 digits (1bi), 3 LEDs per segment (210 total). \$\endgroup\$
    – Falci
    May 10, 2020 at 11:46

1 Answer 1


Can the controller "auto discover" the total number of addressable RGB LEDs?

Sure. You just need to connect the data output of the last LED back to the controller. If you want to create a stackable module, you'll need a loopback cap that goes on the far end. You can stack any number of digit modules between the controller module and the loopback module.


simulate this circuit – Schematic created using CircuitLab

A 10 digits number would have up to 210 addressable LEDs. Is it a problem?


For option 2: Which microcontroller is recommended for this setup?

We don't do product recommendations here.

The key question is whether the MCU has all the necessary I/O to communicate with its neighbors (UART?) and also to control all of the LEDs (GPIO).

  • \$\begingroup\$ Thanks for the reply. I understood the non product policy. Is there a category or generic capability non-brand specific, you could recommend ? I'm totally lost here. \$\endgroup\$
    – Falci
    May 10, 2020 at 11:56
  • \$\begingroup\$ How can I send data out back from the last one, if I don't know who is the last? The idea is to be able to plug an extra digit on the left. \$\endgroup\$
    – Falci
    May 10, 2020 at 15:10
  • \$\begingroup\$ See edits above. \$\endgroup\$
    – Dave Tweed
    May 10, 2020 at 15:47

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