[tech] Re: several messages

[Andrew Williams]

On Fri, 15 Jun 2001 11:00:56 +0800 (WST), Mark Tearle wrote:

>
>Offers of assistance from Adrian Chadd, James Devenish, John West and
>Chris Thorp :)  Cool some momentum ...

>A good vending abstraction layer is probably a good project though,
>with perhaps an implementation of IOTP (Internet Open Trading Protocol)
>to do the dispense credit type stuff.

If you're planning a project that will be useful for other vending
machines, it's a better idea to make the hardware too - documenting how
you've burned a ROM for this particular microcontroller and
implementation won't be very useful.

Personally, my choice of hardware model is AVR's on a SimmStick
motherboard - SimmSticks are a fairly open-hardware project
(www.simmstick.com). You put a few 30-pin SIMM sockets on a motherboard
made of 'veroboard', and then just plug in modules. There are oodles of
free PCB designs as well as pre-etched boards for relay drivers and
other interface boards (including USB and video), as well as an
assortment of CPU boards for AVR, HC11, and 8051.

The 30 pin bus has power, ground, RS232 send/recieve, and a whole bunch
of general purpose digital or analog (depending on CPU and
configuration) IO lines.

The only issue is that running lots of high-current wiring to
connectors on a relay board could make it mechanically unsuitable for a
SIMM socket - the strain from the off-board wiring could cause
problems. In that case, we could use a heavy duty screw-down terminal
block on the end of the 'motherboard' and run that to a non-simmstick
relay board.

So - who's going to turn up to UCC tonight and talk about vending
machine stuff?

Andrew