[OpenTRV-dev] I2C expansion connector round 3

[Richard Chilton]

So, these production boards and this interface, are they intended as a large run of boards for hobbyists to deploy, trial and develop with, or are they also OEM modules for use in a more consumer focussed product?

If both, it's beginning to sound like the classic dev board vs consumer board trade off.

Or am I completely lost? - I feel I'm missing a project roadmap and a little sign saying 'you are here' :o) 


On 8 Sep 2014, at 17:39, Damon Hart-Davis <EMAIL ADDRESS HIDDEN> wrote:

> Hi,
> 
> In some cases there may not be spare pins to allocate, esp on production boards.
> 
> I’m really fighting for pins on our version that’s going though prod engineering right now (just come of the phone with the main man there) and I don’t want the tail to be wagging the dog.
> 
> Rgds
> 
> Damon
> 
> 
> On 8 Sep 2014, at 17:29, Richard Chilton <EMAIL ADDRESS HIDDEN> wrote:
> 
>> Can I ask what the reasoning behind optionalising nIRC/nSC was, as I think the answer will help me understand the requirements better.
>> 
>> Thanks,
>> Rich
>> 
>> On 8 Sep 2014, at 16:18, Damon Hart-Davis <EMAIL ADDRESS HIDDEN> wrote:
>> 
>>> Well, that don’t last long!
>>> 
>>> In response to comment from production engineers I am making nIRC/nSC support optional for now, depending on the main board.
>>> 
>>> 
>>> 
>>> 
>>> 2014/09/08: Revision 3, Note that the nIRQ and nSC lines can be left unconnected on some board variants.
>>> 2014/09/04: Revision 2, 14-pin connector, added nINT and nSC2 after dev mailing list suggestions
>>> 2014/09/03: Revision 1, 12-pin connector
>>> 
>>> 
>>> Aim:
>>> 
>>> Trying to develop a simple I/O extension/shield system for OpenTRV to add more sensors (etc) easily.
>>> 
>>> Also this should allow an easy bridge to other systems such as RPi / BB / etc.
>>> 
>>> This must be simple and small and cheap enough to use in hobby / dev / prod environments and allow (in priority order):
>>> 
>>> 1) I2C expansion.
>>> 2) In-Circuit Programming of AVR.
>>> 3) One-Wire expansion.
>>> 4) Serial off-take, eg for CLI interaction.
>>> 
>>> The connection should ideally be keyable or at least not cause instant destruction if reversed for example.
>>> 
>>> 
>>> Suggestion:
>>> 
>>> 14-way (2x6) pin stackable (pins or socket on board, suggestions please, RPi is pins).
>>> 
>>> 0.1" pitch to be easy for DIY shields, eg with Veroboard as I just did for my RPi.
>>> 
>>> Following pin pattern:
>>> 
>>> MISO * .. * 3V3 (Vcc)
>>> SCK * .. * MOSI
>>> nRST * .. * GND
>>> nIRQ * .. * nSC
>>> SCL * .. * SDA
>>> RX * .. * TX
>>> N/C * .. * DQ
>>> 
>>> a) N/C means No Contact and can be used to key the connector.
>>> b) RX and TX are protected by 10k series resistors from AVR.
>>> c) nRST (input to main board) is active low and is pulled up to 3V3/Vcc with 10K series resistor at AVR.
>>> d) SCL and SDA are pulled up at AVR with 4K7 resistors to 3V3/Vcc.
>>> e) 3V3 can be anywhere from 1V8 to 3V6 absolute; 2V to 3V6 operating.
>>> f) nIRQ (input to main board) is active low and is pulled up to 3V3/Vcc with a 10K--47K nominal resistor and a 1K series resistor: this should be driven with open collector/drain driver only.
>>> g) nSC (output from main board) is the active low select for an SPI device on the bus, 
>>> h) The nIRQ and nSC lines can be left unconnected unless the main board variant explicitly supports them.
>>> 
>>> Features:
>>> 
>>> 1) Top 6 pins can be used directly with 6-pin AVR programmer.
>>> 2) Rest of pins carry I2C (SDA, SCL), OneWire (DQ) and serial (RX, TX, protected by 10k series resistors)
>>> 3) If entire connector rotated boards unlikely to be destroyed instantly.
>>> 
>>> Bit more on (3): RX and TX are safe to short to GND or 3V3 or anything else, nRST safe to short to either rail, DQ/SCA/SCL safe to short to GND.
>>> 
>>> 
>>> 
>>> Note: see alternatives such as http://www.tag-connect.com/ for SPI/ICP part.
>>> 
>>>> 
>>> 
>>> _______________________________________________
>>> OpenTRV-dev mailing list
>>> EMAIL ADDRESS HIDDEN
>>> http://lists.opentrv.org.uk/listinfo/opentrv-dev
>>> 
>> 
>> 
>> _______________________________________________
>> OpenTRV-dev mailing list
>> EMAIL ADDRESS HIDDEN
>> http://lists.opentrv.org.uk/listinfo/opentrv-dev
> 
> _______________________________________________
> OpenTRV-dev mailing list
> EMAIL ADDRESS HIDDEN
> http://lists.opentrv.org.uk/listinfo/opentrv-dev
>