Thursday, 10 November 2011

Word clock

Carrying on our Word Clock project, we managed to get a PCB made for it tonight.
The final PCB was drawn out in our old favourite ExpressPCB (because the free version of DipTrace has a limit on the number of pins you can use in one circuit). It took a while getting used to the rather basic interface again, but it didn't take long before it all came flooding back!

Here's the PCB design we came up with.
Charlie Plex 90 Pcb - Black

It's not really 100% complete, because we've only really run the traces in the horizontal direction. When the LEDs are in place on the board, we'll have to bend some legs over and solder an LED leg to another LED leg -  because otherwise we'd either end up with a really complex PCB layout or crossed traces somewhere:

note that the horizontal LEDs are connected where necessary (e.g. D51-D55, to D45-D50 are all connected) but the vertical LEDs (D5, D15, D25, D35 etc) need to be connected using the component legs

To connect the LED legs in the vertical directions, we'll just solder the legs together, similar to the way shown in this diagram -

Anyway, here's the board after etching and cleaning - getting ready to drill the LED holes.

Almost an hour later, after drilling over 200 holes with a hand drill, it started to look like an array of components might actually live on this board:

With the board drilled (and while we waited for the 150 LEDs we'd ordered off eBay to arrive) we lined up the plastic inserts, that we cut last week, against our PCB. Each LED should sit snugly into each "cell" in the insert -

Bugger. We're out by quite a bit. Having measured the spacing for 3mm LEDs and set the spacing in the insert grid to 8mm (that's 3mm for the LED plus 2.5mm top and bottom for the PCB traces) we're still not sure how we got this one so far out.
But the PCB is made and etched (we've another one in the making too) so it makes sense to redesign and cut the grid to better suit the PCB, rather than the other way around. Maybe it's time to fire up the laser cutter again......