SYNTHINGS is a digital synthesizer development platform that I've been building.

Initial assembly of boards

jason | 26 November, 2010 17:10

The FPGA board had been built a few days ago, and all looked good - it was responding to JTAG requests, at least!

I had a box from an earlier project that was about the right form factor what I wanted, so I designed two boards - an upper User Interface board that would hold the display, the keys and the rotary encoder, whilst the bottom board would hold the power generator, CPU (PIC), MIDI input, and audio jack.

I had some spare long 0.1" pins which I acquired from VTi years and years ago when we stopped making hardware. These would allow the FPGA board to sit between the two boards, and I discovered that both boards fitted in the grooves in the case (although the display would need a bit cut out from the top in order for it to be centred - no biggie).

The top board was the most important, since I could power the FPGA from other boards, and I really needed to make sure I could drive the display correctly.

I initially powered it up, and made sure that I was getting the 19.2V required for the LCD backlight - 19.26V was what it was reading, which was well within tolerances - so I created a simple Verilog test pattern for the display and plugged it in.

Nothing happened. Not even the backlight came up.

After verifying that everything was bouncing up and down or steady, I noticed that the tracks for the backlight were in the wrong place - I'd wired up all the tracks starting at the left hand side, rather than the right hand side.

That either meant that I'd made a huge mistake in the design of the connector in Eagle, or that the screen's cable was meant to go under the PCB.

Luckily it was the latter - I simply flipped the display upsidedown and the backlight came up. I then tweaked the Verilog a bit to get the pattern to display (I'd inverted the display's reset line).

RevA UI board with sample display pattern

The board would need to be redone to put the connector on the underside...

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