DSP TU Part 3

This is part 3 of the DSP terminal unit project. Part 1 was a proof of concept using a PIC32MZ evaluation board. Part 2 is the initial PCB design and further firmware development. The revisions are:

Rev A - Original version. Display connector is backwards, so the display has to be hand wired instead of just plugging it in. Otherwise, the board is good.

Rev B - Fixes the display connector, adds test points, and resizes the board to fit an extruded aluminum case.

Rev C - Changes board outline and mounting holes so the board can fit in a plastic case.

Figure 1 shows the front of the unit in its plastic cabinet. It appears I made an error when ordering the PCB that is used as the front panel. It is supposed to have white lettering on blue soldermask (as is correctly done on the rear panel), but there is no soldermask on the board. The front panel works, but is pretty shiny.

The front panel board fit is very tight in the corners. In the next revision, I would put a diagonal cut across each corner. On this revision, I did a diagonal cut on each corner using diagonal cutters.

The hole for the display is a bit wide on the right side. This was done to allow the flat cable from the display glass, which exits the glass at about the middle of the glass depth, to make it to the edge of the display PCB without being crimped by the front panel.

To assemble, the front panel PCB is put in the plastic case, then the DSP TU PCB is slid forward to rest against the front panel. The display board is typically leaning back a bit. A drop of RTV adhesive can be put between the display board and the front panel PCB, then the top of the display board is pushed forward so the display glass is in the front panel cutout and the top of the display board is against the back of the front panel PCB. The two can be clamped together until the adhesive cures.

The enclosure is a Heyiarbeit DFC3500GP0402. There are 12 plastic spacers molded into the bottom of the case. The PCB is mounted using three of these spacers. Some of the spacers interfere with the leads of through hole parts protruding from the board. These spacers can be cut off with diagonal cutters. The PCB is mounted to the bottom of the enclosure using three M3 x 6 pan head Phillips screws with a 0.50 pitch.

Parts List

Main PCB
- KiCAD Files
- Bare or Stuffed Board from PCBWAY - On the right side of the page, choose bare board or assembled.
- Digikey List
Heyiarbeit DFC3500GP0402

References

DSP TU - Proof of concept on Microchtip evaluation board

DSP TU 2

Figure 1 - Front panel

Figure 2 - Rear panel

Figure 3 - Interior