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I have a 4 x 8 matrix of RGB 8-segment displays, (short for a 7-segment 'digit' plus a dot pixel, for which each segment (as well as dot) contains: 1x red LED, 1x green LED, and 1x blue LED).

To drive them, I will be using the TLC6983 [DataSheet]. This driver multiplexes the LEDs using 16 scanlines, however, I need to determine the scanline groupings.

Question

What are the tradeoffs between scanline configurations when dividing the matrix into differently shaped subsets? Does simultaneously enabling LEDs localized in a compact area (and then not at all for an increased duration) improve or worsen characteristics such as:

  • Thermals
  • EMI
  • Anything else

Example scanline configurations

qty spatial
relation		 shape @ segments
/ digit
2 adjacent rows @ 1
4 adjacent columns @ 1
2 adjacent digits @ 8
4 distributed rows @ 1
4 distributed columns @ 1
2 distributed digits @ 8
16 distributed digits @ 1

I assume that scanning on distributed shapes (example: rows 1,3 then 2,4) is thermally better than adjacent shapes (example: rows 1,2 then 3,4), but maybe if everything is cycling at such a high rate, it doesn't matter.

kando
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    Could you clarify 4 x 8 x rgb 7seg+dot ... do you mean you have 32 digits each of 8 LED triples? Ie 256 red + 256 green + 256 blue LEDs, a total of 768? – jonathanjo Jul 20 '23 at 12:00
  • @jonathanjo : Totes that exactly : j – kando Jul 20 '23 at 12:32
  • @jonathanjo : Edited for added clarity. – kando Jul 20 '23 at 12:34
  • Usually you'd organise it for best PCB layout, which keeps your lines short and organised, with the fewest vias. The other consideration is organising the scan rate to be as fast as possible to reduce flicker -- some people notice much faster flicker rates than others. Thermal makes no difference because persistance of vision is much faster than the thermal conduction. – jonathanjo Jul 20 '23 at 12:39
  • Oh yeah, flicker is assumed to be ≥ 2 [kHz] and layout will be optimized — the IC will be dead center in the LED matrix and there will be a fair number of layers. That leaves the remaining question : Does simultaneously enabling LEDs closer together or farther apart have any effect? – kando Jul 20 '23 at 12:44
  • What power of LEDs do you have? – jonathanjo Jul 20 '23 at 17:50
  • Electrical or luminous? V.f.blueGreen ≤ 3.5 [V], V.f.red ≤ 3.0 [V]. I.f.nom = 20 [mA]. I_v.nom < 100 [mcd] after PWM. – kando Jul 20 '23 at 18:54
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    I struggle to think of anything (other than might be seen with photography) that would be different solely changing the multiplexing pattern. – jonathanjo Jul 20 '23 at 19:01

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