stefan, thank you for your responses
Quote from stefan on September 29, 2011, 13:44
So glad to hear kids doing SMD work in school and getting great results - really encouraging! In my head I was imagining designing for SMD for convenience and cost. Not sure I can see how I would route single sided, but that said I haven't tried yet!
I am thinking the first thing to try is a "no-components" board, i.e only plugs, sockets and headers with no resistors or Schottky diode protection. That might be enough for experts to get started.
Paul Gardiner uses 1206 size components, the extra bit of size makes it easier. It also means there is enough clearance to route a track underneath them (though that makes DIY boards, with no solder mask, harder to solder).
I am thinking a little 'stand' to support anything sticking down under the board would enable kids to make the whole board with solder paste. Something like Meccano U-shaped beams might work.
Another thing to perhaps brainstorm together would be the way we might hope to physically design the breakout for ease of use. With a SMD 1.27mm socket and a TH 2.54mm header on a single sided board we can pass the signal through easily enough.
I was initially thinking, maybe SMD 1.27mm plug on the breakout, and use a very short ribbon cable.
I am worried about noise, so another thought is to get ground between the signals using two PCBs:
1. Plugs straight into R-Pi (with a 1.27mm plug), and then it has a socket which carries the signals to the actual breakout via a less noisy cable (probably still 1.27mm, but 2x connections).
2. Breakout board which gets the less-noisy cable inserted, and expands the live signals to DIL breadboard friendly headers.
Not worth trying until we know noise is a problem
Ideally the production R-Pi would have the socket near an edge to minimise cable length.
How would this work with your breadboard idea though? Would you want a two row header split by 7.62mm to span the centre gap on a breadboard like a DIP package?
It could be 0.3", or 0.6", and could fit straight into DIL IC sockets.
If everything worked perfectly, it might be nothing more than an IDC DIL connector
So the breakout PCB is actually at the R-Pi socket end, and the ribbon cable connects from that into a breadboard, veroboard or PCB.
Would you want it to protrude on a tab from one side of the R-pi so that access around the breadboard is easier? How would other people use their breakout?
I don't know, I'd need to experiment with it.
I certainly think the R-Pi socket needs to be close to the edge.