Nigel Goodwin said:
I've seen a LOT! of development type boards, and even have a number of them - but for my tutorial series I decided on a modular system - it's far more versatile, and the boards are simple to make on veroboard. You do obviously have the added expense of the connectors, but I think it's well worth it!.
Well, my design will be modular
. I can think of MANY different 'attachments' it just depends on how often I'll need them. 'Modules' used quite often will be on seperate daughter boards, with a standard header matching that of the main board (for ribbon cable/IDCor socket) and ones used very regularly can go on the main board, depending on how large their circuits are.
I did consider making a 'piggyback' board, which would be the same size as the PIC, with all pins of the socket going straight trough the board, for breadboarding, and under the PIC, a max232 for bootloading, an ICSP header, and osc. I've done a rough design in eagle, looks good, and doable. But alas, of course, I don't want to make up the power section every time, so for a basic dev board, here's what I think it will definately need.
*Power - DC power jack, 7-12V, regulator etc.)
*Osc - osc socket/crystal socket, and RC osc. Did this for my CPLD board, proved to be very handy, and the whole osc seciton measured 20mmx20mm. All set by jumpers.
*ICSP header - obviously. Possibly with isolation circuit, but not really needed.
*RS232 with max232. - bootloader/general serial comms.
*Header for every port. Each with its own +V/GND
Now, I'm pretty sure all of that could fit on a small board. I've learned some lessons from my CPLD board, high value pull-up resistors for one thing, anythink under 8.2k seems to allow a lot of current to flow (especially with 1k pull ups, and 33I/O's, 5ma per pin = 165ma). As for the 'cost of connectors', I happen to have loads of pin headers and sockets here, doing nothing
Optional extra's shouldn't take up much space. As I said, these will simple be 'app specific' headers. No point in having an LCD on board when I could just have a connector, or even use a serial LCD. And things like SPI/I2c would simply come straight off the pins or the headers for those ports. Buttons/LED's/7-seg's/DAC's can all be on external boards, as I could do this with stripboard, and not have to order another batch of PCB's.
Of course, it can't do everything, but I don't want to get a PCB made up only to find I've left something useful out, meaning I have to breadboard something every time I want to use the system, I'll keep it down to the minimum though. This won't be a 'beginners' board, probably not the sort of DIY design that anyone could do, its just a way for me to prototype, using a high-end PIC (all useful peripherals). Its a useful exercise for PCB design, and it uses up some of the components I got laying around here (PIC's, connectors, crystals, DB9's etc..)
Thanks for the advice, good to know you guys are here,
Blueteeth.