Elektor Vocoder, part 2

Moving on with this project, it was finally time to continue by etching the back planes and a few filter boards. Since the UV unit I use for exposing the photosensitive boards (a low-power EPROM eraser) is very far from perfect for this use, the back planes turned out almost a complete failure. Here’s why:

First, low-powered means that a single board has to be kept exposed for around 30-45 minutes to get decent results. Second, this exposure time depends a bit on the brand of the board (different coating solution and/or process per manufacturer, I assume), so whenever I try out a new brand it’s a bit of trial and error. For this batch I had a new brand, of course. Third, as the UV unit is meant for erasing EPROMs it has only a single small lamp, meaning that large boards (such as the backplanes) need to be exposed in several parts. For large boards it’s not uncommon to have overall exposure times as long as 1,5-2 hours with this UV unit! Just for comparison, a real PCB exposure unit handles boards of almost any size in 5-10 minutes per side.

So I guess what happened was, that all these issues combined with my crap etching tank (a simple plastic container) simply produced too many variables to handle. And as “..almost a complete failure” denoted earlier, I spent quite a while doing trace repairs because of this.

Repaired backplane traces

Not that it wasn’t anything a multimeter, good length of wrapping wire and heaps of patience couldn’t fix, but a total nuisance nonetheless.  Finally, with the trace repairs out of the way, I was able to spend a moment or three admiring my “modular”. Yay\o/

Backplane with boards attached

Present Day Update: Come to think of it at a later stage, constructing the backplanes out of stripe-plated perfboards would’ve been a much more functional and faster approach given the etching results with this first batch.

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