AVC: Serial to I2C Bridge

I finished designing, etching and silkscreening a new board last night and started populating it. It’s a slight redesign of a board I did before last year’s AVC. What’s it for? Not telling yet. 🙂

I can say this. It’s an Arduino clone that will speak serial on one set of pins via NewSoftSerial and I2C on the standard set of pins. It has an FTDI header for programming via bootloader.
AVC Serial to I2C BridgeThe design implements some suggestions on reset and decoupling circuitry from teslafan @ Robotic Core based on an Atmel application note (doc2521.pdf).
The board will interface a Top Secret serial-only device to the mbed via I2C. Which seems like a waste of an AVR, except the little processor will also be doing some data processing and filtering. I already have code written for the board on which this is based.
Why not use the super-powerful mbed for this processing? Maybe in a later revision I will but I burned out one of my mbed’s UARTs and have no more to spare. I don’t want to spend $60 on another one at the moment.
AVC Serial to I2C Bridge
The serial device is 5V and the mbed is 3.3V so I attempted to do some logic level shifting but I was in a hurry and I botched it. I have a uni-directional level shift in place on the SDA line which is supposed to be bidirectional. Rats. Fortunately I have a simple fix; throw a current-limiting resistor in place of the diode and remove the pull-up resistor.
 For more detail: AVC: Serial to I2C Bridge
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