[OpenTRV-dev] I2C expansion connector round 3

[Damon Hart-Davis]

Hi

We need something NOW for the prod eng / consumer board to let us program in place and we also have a secret hush-hush IoT thing going on where we may want to stuff as-yet-unknown sensors in easily.

I also want to make the R&D/hobbyiest boards as easy to extend and connect as possible, eg with a single bridge board to the RPi, long overdue.

And I don’t have time to do it perfectly, you know the story.  I’ll have cheese with my whine, thank you!  %-P

So, yes, compromise.

The prod eng guy had my connector in his schematic withing about 5 minutes of me sending it over, and I didn’t want to hold back our discussions today at all as I’m back at the day job for all or most of this week!

Project roadmap?  What a good idea; I’ve heard of those!  (Today was meant to be partly planning time, but, well…)

Rgds

Damon


On 8 Sep 2014, at 18:28, Richard Chilton <EMAIL ADDRESS HIDDEN> wrote:

> 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.
>>>> 
>>>>> 
>>>> 
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>>>> 
>>> 
>>> 
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> 
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