Wednesday, 3 August 2011

Guitar PCB take two

Not only are we trying to make a working miniature guitar, we're also trying to find the best (and easiest) way to make a number of them, in a way which is consistent and repeatable. So far we've managed to make a working instrument, but it was really fiddly to make, and for anyone else to try to follow the same steps, it'd be pretty hit-and-miss as to how successful the end result would be (we're not mentioning that our guitar didn't actually fit into it's enclosure!)

So we're trying out an old idea again - making the neck PCB from fine (0.2mm) traces and connecting via a ribbon cable at one end. Here's the design toner transferred onto some copper clad board:



The board was cut to size to make sure it fit along the guitar neck. In fact, we can be quite loose with measurements and tolerances- at this stage, once we have a working PCB design, we can always amend the acrylic shape(s) to fit the PCB if necessary



Then the board was etched and the edges sanded and finished off nicely



Some half-pitch IDE cable was attached (I think this is 0.025" pitch cable. Whatever it is, it's about half the pitch again of "regular" hard drive IDE cable). This was acheived by tin-plating the end of the PCB first (it was too big to fit inside the glass jar we keep our tinning solution in)



Using our new tin-plating and solder-paste technique, the ribbon cable was actually quite easy to attach, even with a big fat pointed tip on the soldering iron. Maybe the fact the IDE cable was made up of single solid cores helped.

The larger "blob" of solder came off the tip of the soldering iron when we started the second piece of multicore cable. It's actually a tiny little bit of solder, but looks enormous on this photo!

The cable ends were checked for continuity and the new-style PCB put into place to make sure the ribbon cable wasn't too wide for the opening



Compare the amount of loose wire with the new board and the old one. With the new board, we could simply loop the multi-core cable under the entire main board PCB and attach to an edge connector.



We considered an alternative - creating a single, solid piece PCB for both the body and neck in one go. This has the advantage of being easier to assemble (although etching requires a shallow bath rather than our preferred "dunk-in-a-coffee-jar-of-gunk" approach) but the downside is that the guitar neck would appear lower than the guitar body (once the acrylic top layer is in place).



We were keen to keep the guitar fingerboard higher than the guitar body so that it accurately reflected the construction of a real guitar



To date the only way we can see this working is to have the guitar neck as a separate board, attached to the main board via a ribbon cable. If we used a single piece PCB, we could make the acrylic of the guitar neck from 3mm instead of 5mm to reduce the height (reducing the position of the body part of the PCB) and introduce a layer on top of the neck PCB, making it appear raised higher than the body?