Sunday, July 10, 2016

Homemade Handheld Videogame Console: Part 3: Building

When my case was fresh off the printer, I started lining up all the components to see that everything would fit as I'd planned. I think I had convinced myself that I would have gotten at least one measurement wrong somewhere and that this first print would be just a test run. I was happy to discover that I had actually not stuffed up anything too critical and that I could get it all to work. The thing that didn't really work as well as I had hoped was the standoffs for the smaller components (amp and boost converter): I had designed a cylinder to fit through the small mounting holes on these PCBs with a diameter of 1.6mm, but when they came out of the printer, these parts of the structure were just a stringy mess: I guess they were just a bit below the resolution the printer was capable of. The standoff cylinders for the pitft screen and RPi mounting holes were 2.5mm diameter, and these came out fine, but they were pretty fragile. In the end, I decided to break them off, drill 2 mm holes in their place and screw the pitft, RPi and larger holes on the boost converter onto the standoffs: lesson learnt for next time!

Once I was happy that everything would fit, I started assembling the buttons, RPi and screen into the case. I cut two square(ish) sections from perf board to hold the buttons (main buttons and dpad) on either side of the screen, and drilled 2 mm holes into these so I could screw them down to standoffs on the case. Buttons were then soldered on before screwing the perf board onto the case.

At this point I realised I'd miscalculated the heights of the standoffs for the dpad side: it was short by about 2 mm such that the buttons would be pressed down permanently upon screwing it in. I didn't have any washers that were small enough, so, because I'm super impatient, I improvised with snipped off bits of wall plugs :) ... Total hack, but hey, it did the job. A little bit of bluetack on the back of each button stopped them from have that slightly annoying rattle.

I then screwed in the tft screen to the case; the RPi would then slot on top of the 40 pin header; conveniently the tft also provides an additional breakout of this same header, which I connected a 40 pin ribbon cable connector to, chopped off at one end so I could feed out the GPIOs/ground to the buttons and 5V/ground in from the boost converter. I soldered up all those connections, plugged the pi on top and powered it up to check all the buttons were working well.

Next I wired up the amp to the speaker, and positioned these in the case. The standoff pins in the case for the amp hadn't come out properly in the 3d print, but it was ok with no further modification, found the board could sort of float in the case with no issue. Next step was to screw in the boost convertor to the case using two of the four mount holes. Soldered the power out pins to the RPi (via header cables) and across to the amp.

Placed the battery into the case, held in place with a tiny bit of gaffer. I fit the slide switch into its hole in the case and soldered it on to the boost convertor. Last step was to solder the signal pins from the amp to the solder points on the RPi PCB that sat adjacent to the 3.5 mm audio jack. Closed the case up, switched it on and everything was working a-ok!

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