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

[Damon Hart-Davis]

Hi

Yes I mean RTS.

No, the idea is to move the FTDI to a shield board.

Our FTDI cables supply 5V!

Rgds

Damon


On 8 Sep 2014, at 20:11, Richard Chilton <EMAIL ADDRESS HIDDEN> wrote:

> Do you mean RTS on the FTDI cable and does that mean there is still a full FTDI header on the new design?
> 
> It's probably not an issue, but be aware that some FTDI cables supply regulated 3v3 on VCC line.
> 
> 
> 
> On 8 Sep 2014, at 19:34, Damon Hart-Davis <EMAIL ADDRESS HIDDEN> wrote:
> 
>> 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.
>>>>>> _______________________________________________
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>>>>>> 
>>>>> 
>>>>> 
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