Head Up Display  (HUD)  panel

      Backlight for "thin" panels

 HUD panel
Introduction

The AIR COND panel is the first panel for which I made the panel backlighting using a circuit board as "carrier" for the LEDs. The thickness of the AIR COND panel is 7.4 mm, so after cutting the rear side of the panel to make it "hollow" there is sufficient space for the circuit board (PCB) with SMD LEDs mounted on it. However, the thickness of the HUD panel is just 4.8 mm, so the "depth" is not sufficient (if you want to keep the panel strong enough).

Backlight for the HUD panel

The backlight circuit board is made using the same approach as used for the AIR COND panel. So, these picture show the placement of the LEDs.
As the panel is hollow, you can use insulated wires to connect "planes of copper" that must be connected to each other. Make sure that the copper underneath the mounting screws of the switches is either part of the "ground plane" or insulated. The switches also make contact with the metal backplate, and the metal backplate will make contact with the frame of the console, so if the copper underneath the mounting screws is not insulated or connected to ground, this  will  cause a short circuit!

HUD backlight PCB HUD backlight PCB on backplate

It is always cool to see a panel when the backlighting of the panel is switched on.

HUD panel HUD panel backlit

The solution for the thickness of the backlighting PCB plus SMD LEDs, if the panel itself is relatively thin, is simple, yet elegant. I used the rubber of the inner tyre of a bicycle wheel. This stuff has several advantages. It is easy to cut to the desired shape, it is already black, and it is a "soft" material, so with little pressure the rubber prevents (light) leakage between the panel and the backplate.

  1. First, cut 4 pieces of rubber from the inner tyre. The width of the rubber pieces is just 2 to 3 mm, just like the width of the edge of the panel (the rest inside the panel is cut with the Dremel). Check that the rubber fits on the edges of the panel. Especially, check that when you look at the face of the panel, you do not see the rubber "protrude" somewhere along the edges of the panel.
  2. Cut 4 pieces of double-sided adhesive tape, one for every edge of the panel. The width of the tape is also just 2 to 3 mm.
  3. Stick the pieces of adhesive tape on the edges of the panel, then stick the rubber pieces on the tape.
  4. Finally mount the backplate.
With this approach you can close gaps of 1 mm. My guess is that if the gap is wider, you can glue a second rubber "seal" using double-sided adhesive tape.

Remark
Note that due to the PCB, the screw that mounts a switch will also "go deeper" into the rear isde of the panel. You may cut some extra depth around a switch in the rear side of the panel, but if the panel is thin and you do not want to take any risks, you could also make the hole in the PCB as large as needed so that the screw mounts directly on the backplate. If the PCB "moves around" on the backplate in the rear side of the panel (because the PCB is no longer held by any screw), you may use a minimal droplet of glue between the PCB and the backplate (after positioning using the panel).

HUD panel with rubber seal
Rubber "seal" between panel and backplate