Thursday, 4 August 2011

We're through with drilling

See what we did there? Through with drilling? Because we're only drilling the PCB to allow us to use through-hole components. Clever huh?

Honestly, when you have to explain a pun it makes it really lame.
Anyway, in the search for an easy-to-make circuit board that can be soldered quickly and repeated easily, and since we're trying out old ideas once more, we've decided to give SMT a go again.

This time, things will be different.
For a start, we can tin-plate the PCB before soldering. We already know that this makes soldering easy, to the point where we're able to solder tiny 0.025" pitch cable to an edge connector on the board.

In fact, using the tin-and-solder-paste method, we attached the multi-core cable much quicker than we ever could if we were using the older method of splitting the cable and soldering each strand through a series of 0.1" pitch holes.

With all this in mind, we figured we give SMT a go again.
We've already got a selection of SMT components in our tool box - mostly 1206 sized resistors and capacitors, and some SOT23 darlington transistors. The SMT crystals from Farnell are the same size as the through-hole versions, only with tabs instead of legs.

The only thing we haven't got is an SMT version of the PIC 18F2455 microcontrollers we've been using. But we thought we'd print out an SMT version of the body PCB and see if the components we had were suitable.



In this example, the ribbon cable(s) to connect the main board to the neck is our tiny 0.025" pitch IDE ribbon cable. We already know we can solder this to the edge connectors, quickly and relatively easily.



Another benefit of using SMT components is the non-copper side of the PCB will be completely empty and we'll have no nasty spiky bits of wire poking through the bottom. So we'll have a nice, low-profile board, a flush reverse side that we can stick straight onto the underside of the guitar top, and no nasty messy tangle of wires like we had on our first attempt.

Of course we'll still need to keep the two rows of six holes along the top and bottom edges of the PCB, since the strummer strings still need to pass through the board from the top of the guitar. But this new layout now requires only 12 holes instead of the seventy or so in the original design.

Inspired by Crazy Dave in this eevblog video (below) we reckon soldering a whole load of SMT components might actually turn out quicker than using their larger, chunkier, through-hole versions.



In fact, if the prototype board works we might just head over to http://www.quick-teck.co.uk and get some double-sided boards professionally made up. Check the spelling to get your browser over there!