[SpiROSE] Led panel assembly and slice format

Led panel assembly

One major issue to design our two PCB was the board to board connection and the led panel position.

In order to have a 80 pixel horizontal resolution with only 40 columns per panel, we need to have the rotation axis between two columns, as the following image shown :

This means two things :

  • The panel axis is not the same as the rotation axis, they are shifted by 1.125mm (half a column), thus the steadiness of the whole must be fixed by adding weight on the rotative base
  • As the panels are meant to be perfectly aligned with one another, the leds and holes has to be symmetrical to the panel axis (not the rotation axis) in order to be face to face with their clone on the other side

For one panel, the connectors are symmetrical to the rotation axis, but when we rotate it by 180°, the connectors don’t align with their clone. This is shown below:

The connector on the rotative base have to be shifted by 2.25mm between the two lines.

The holes on the rotative base also have to be shifted by 1.125mm from the rotation axis to be aligned with the ones on the panel.

Consequences on the framebuffer and slices format

At a given position p, a column on a panel and his clone on the other one display the same voxels. Thus only 40 columns out of 80 are displayed. We have to wait half a turn to reach the position p again, but now the panels have rotated by 180° so the new 40 columns are the ones missing. Therefore we still have our 80 voxels wide resolution.

Hence a slice is displayed in two steps :

  • the even columns first
  • the odd columns half a turn later

This could be handled by the framebuffer module, but would imply to remember at which position we are. In order to remain position agnostic, it is better to let the SBC directly handle this by outputting the slices in an adequate format.

The SBC will cut a slice in two batches, one with the even columns, the other with the odd ones. However, because the panel rotate by 180°, the odd columns need to be reversed to be displayed correctly. All of this is shown in the following figures:

Let’s assume we want to send this slice

At position p we will display the even columns

At position p plus half a turn we will display the odd columns

Thus the SBC will send the slices with the following format

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