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

[Richard Chilton]

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
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>>> http://lists.opentrv.org.uk/listinfo/opentrv-dev
>>> 
>> 
>> 
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