I think we should come up with a standard dimension for the boards, so that brackets with the same dimensions could be designed. Preferably square formed, right? That means you can put the boards in four different directions to get wires and such in the preferred direction.
i think this standard should only be applied to the PCB versions of the boards. people making their versions on strip board can make them whatever shape they like.
when writing up documentation we should include Eagle PCB layouts. standard size. standard mounting hole position.
i think putting the power connector and i2c bus connector in a uniform place be a good idea too.
i hadn't considered the advantages of making them square but now you bring it up i agree.
we also want a standard connector type.
i would recommend something that fits on standard header pins. this way we can just use header pins on the boards and make up cables to go between them.
standard header pins also fit the standard hole spacing of solderless plug blocks and strip board.
to connect to the header pins i recommend http://www.molex.com
wire-to-board crimp connectors but these require a (fairly cheep) crimper so maybe someone else has a better idea?
we also need a power standard.
i think any board without it's own regulator should receive 5v.
does anyone think we need a 3.3v supply? personally i think 5v is a better choice and people can regulate down to 3.3v if they need on a particular board.
most projects will need at least one board with access to a higher voltage. this will be needed for power regulator boards as well as any board driving higher voltage components (DC motors for example).
it should be encouraged to allow for a large range of input voltages here (5.5v to 14v ??) but i think we should leave the exact operating voltages up to the board designer to allow for different modules servicing a wide range of applications.
i would recommend we use a different connector type for higher voltage connections to allow for higher power draw as well as preventing accidental mis-wiring of high voltages to delicate components.
as for the communication standard between boards, i'm working on a prototype implementing the ideas i put up in the doc here: http://docs.google.com/View?docid=ddp2r5j8_21dgt72qgz
i have most of the code written and i'll be able to test it on boards i already have.
hopefully i'll be able to get it compiled and tested later this week.
i'm not a great programmer so if someone else out there is welcome to completely rewrite it but i feel we need a working prototype that people can modify to suit their application.
my code runs on the AVR atmega8 platform but should be easy to port to other AVR platforms (including Admin's Axon).
i've only been talking about the electronics side of this project. obviously there are still a lot of decisions to be made about the mechanical components.
so, things that i'm presuming are decided: (please comment if anyone disagrees!!)
- it should be possible to build boards on stripboard etc but PCB versions are encouraged.
- PCB versions of boards should be square and of one of several set sizes.
- inter module communication should be by either UART or i2c and should not conflict with packets of the format described here: http://docs.google.com/View?docid=ddp2r5j8_21dgt72qgz
even if they don't require that format to operate correctly.
- any microcontroller (or microprocessor) type is acceptable as long as it can be made to operate within out list of standards.
- logic components will be 5v tolerant or have buffering within the module to accept 5v I/O.
- modules not accepting 5v input but taking a higher voltage will have a voltage regulator capable of acting as a power bus to other modules.
- connectors between modules should fit onto standard header pins.
- standards should only be applied to modules where necessary for them to inter operate with other modules. if a module does deviate from our standards though it should be made clear in the documentation for that module.
things we still have to decide: (please add to this list!!)
- standard board sizes (for PCB versions only). i think we need more than one. and something that converts between inches and mm easily... multiples of 1.5inches ~ 40mm...
- connector type suggestions.
- minimum acceptable documentation. i think we need parts list (with links to suppliers where applicable), estimated cost, links to any required software, detailed step by step instructions (with pictures if applicable), any code should be well commented, any more???
- licencing. who owns this? how do we stop someone else from patenting out work? i think we need a template Open Source type licence that anyone can copy into their project.
any one disagree with anything in the summary?
anything to add?