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

[Bo Herrmannsen]

Thumbs up from me.... but now i'm the scared cat up in the tree wondering
how to fit that on an opentrv board....


2014-09-03 20:03 GMT+02:00 Damon Hart-Davis <EMAIL ADDRESS HIDDEN>:

> Hi,
>
>
> 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:
>
> 12-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
>  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 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.
>
> 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.
>
> Rgds
>
> Damon




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|  Bo Herrmannsen                     |
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| "blessed are the "cracked",         |
|  for its they who let in the light" |
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