[OpenTRV-dev] I2CEXT connector second pass: comments please.

[Damon Hart-Davis]

RESET would be driven from RTS via a cap as usual for Arduino-like bootloadable boards.

We don’t need no stinkin’ flow control.

We could supply 3V3 (ie main board power) from the FTDI via a local reg.

Rgds

Damon

On 8 Sep 2014, at 16:35, Richard Chilton <EMAIL ADDRESS HIDDEN> wrote:

> This picture may help visualise. When connected the FTDI would be horizontal with only Rx, Tx, and GND connected, so flow control and reset go out the window.
> 
> MISO * .. * 3V3 (Vcc)
> SCK * .. * MOSI
> nRST * .. * GND
> nIRQ * .. * nSC
> SCL * .. * SDA
>  RX * .. * TX .. .. .. GND
> N/C * .. * DQ
> 
> 
> 
> 
> On 8 Sep 2014, at 16:16, Damon Hart-Davis <EMAIL ADDRESS HIDDEN> wrote:
> 
>> I’ll see if that makes Bo cry, but I think he was suggesting something vaguely similar…  Would be nice if it can work (I’m not able to see in my head what you mean at the moment.)
>> 
>> Rgds
>> 
>> Damon
>> 
>> 
>> On 8 Sep 2014, at 15:41, Richard Chilton <EMAIL ADDRESS HIDDEN> wrote:
>> 
>>> If you add an optionally fitted ground pin that lies 0.3 inch east of Tx, you could get an FTDI cable on there when there was no shield installed. Possibly a crazy idea, I've not had coffee yet this morning!
>>> 
>>> The rest looks a sensible approach to exposing an interface en masse to shield or ribbon cable for development purposes.
>>> 
>>> No other useful feedback, one piece of pedantry though: 14 way is 2x7, not 2x6 
>>> 
>>> -- Rich.
>>> 
>>> 
>>> On 4 Sep 2014, at 21:12, Damon Hart-Davis <EMAIL ADDRESS HIDDEN> wrote:
>>> 
>>>> OK, thank you for feedback so far dear opentrv-dev!
>>>> 
>>>> Here is a second go.  Didn’t have quite the energy/time I was hoping for this evening!
>>>> 
>>>> This is checked into the public repo under docs, BTW...
>>>> 
>>>> 
>>>> 
>>>> 2014/09/03: Revision 1, 12-pin connector
>>>> 2014/09/04: Revision 2, 14-pin connector, added nINT and nSC2 after dev mailing list suggestions
>>>> 
>>>> 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, 
>>>> 
>>>> 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
>> 
> 
> 
> _______________________________________________
> OpenTRV-dev mailing list
> EMAIL ADDRESS HIDDEN
> http://lists.opentrv.org.uk/listinfo/opentrv-dev