Pushing ArduinoISP sketch to Arduino Uno
so that I can use it as Programmer

Pusching I2C master program to First Satshakit

Now pusching I2C slave program to Arduino Uno

Here is the output of communication on the serial monitor
connected to Arduino Uno (I2C Slave)

First Satshakit and Arduino Uno connected (for both ISP programmer step, and I2C step, as it is not using same pins)

Pushing the Slave programm the the second Satshakit

Second Satshakit connected to Arduino Uno during this second step

The 2 Satshakit are connected together via 2 wires (A4toA4, A5toA5) for the I2C communication. NB: there is no Arduino at all in the final validation schema.

Yhe power is provided to the 2 boards using the power of the FTDI cable and I have connected the Rx pin of the FTDI cable to the Satshakit Slave in order to get the output of the master/slave communication

Here is the Neil's original I2C bridge (master) board. See the related .png and .rml files in the ouputs at the top of the page.

Here is the Neil's original I2C node (slave) board. See the related .png and .rml files in the ouputs at the top of the page.

Here are my boards, after milling and soldering

Trying to burn the Board from my Arduino IDE
It is not working

To solve this issue (that I already encountered in the past and which is probably related to the version of my Arduino IDE, v1.6.12, last version)
I burned using the following command in my command line: "avrdude -C/Applications/Arduino.app/Contents/Java/hardware/tools/avr/etc/avrdude.conf -p t45 -c usbtiny -P usb -e -Uefuse:w:0xFF:m -Uhfuse:w:0xD7:m -Ulfuse:w:0x62:m"
which is just a variant of the command line that Arduino IDE is lauching (but using a different avrdude, and a different avrdude.conf)

Now that both I2C master and node are burned I can start programming on them
but before I need to install a libraries TinyWireM (from Adafruit)
and TinyWireS (from http://playground.arduino.cc/Code/USIi2c) that manage I2C,
also I added a Board Manager from https://github.com/SpenceKonde/ATTinyCore

First I did the programm for the Slave
In a very first time it was just a Led blinking to check if card is wworking fine
then I added logic of receiveing a transmission from I2C master

Then I did the programm for the master
At the starting I integrated a software serial logic to see what Master is doing in the loop (in the Serial monitor)
But it was consuming too much ressources
So I disbaled this software serial logic

I first pushed my programm to the slave
Then I pushed my programm to the Master
But I connected I2C network before doing this, and looks like I damaged my ATtiny
No more possible to programm it, Burn it, or to Read it (via command "avrdude -v -p t45 -c usbtiny -P usb -U flash:r:test.hex:i")
So no other choice than changing the At tiny on the board :-(
Unsoldering it with my "heating pistol" (first time I use it)

Now re soldering it

Then I was able to push programms to Master again
And I got the result
My program is working, but looks like my slave is not catching each value from master
so the frequence of blinking is not the one specified b ythe master
probably a communication issue, need to work on it more, perhaps playing with Pullup Resistor values, I read a bit about it ...

Here is the Eagle schematic view of the board.
See the related .sch file in the ouputs at the top of the page.

And here is the Eagle board view of the board.
See the related .brd file in the ouputs at the top of the page.

Here is the board, after milling and soldering