[TriEmbed] A Few Questions - Hopefully not stupid ones

[Chip McClelland]

All, 

I am building a new board and have to make some design decisions. Before sending to OSHPark, I wanted to see if you all could tell me if I am about to make any mistakes:

1) Powering a Bluetooth LE module using an Arduino IO Pin.  I am using the Adafruit Bluetooth LE friend.  According to this article <https://learn.adafruit.com/introducing-the-adafruit-bluefruit-le-uart-friend/current-measurements>  it should only draw 15.2mA peak current.  Looking up the ATMEGA 328p specs <http://playground.arduino.cc/Main/ArduinoPinCurrentLimitations>  I see that that it can source 40mA on an IO pin.  I know that engineers like to add a “safety factor” so, do you think I would be OK or should I use a FET and have the Arduino simply control it?

2) I am moving away from storing data on a MicroSD card and want to use a FRAM chip instead. BTW, if you have not looked at FRAM it is awesome!  I will use the Fujitsu chip <http://www.fujitsu.com/us/Images/MB85RC256V-DS501-00017-3v0-E.pdf> and communicate using i2c.  Here is the question, what if I wanted to use an external reader to extract the data from this chip, I could expose the i2c pins on the boar and use a POGO pin reader to connect - that way I would not need to refresh the ATMEGA on the board to change to a data dump sketch.  So, I would connect this device to provide power, ground, SDA and SCL.  The thing is, I don’t want the ATMEGA on the board to get in the way of this.  Could I simply add a pin connected to the board’s RESET pin and hold it low, disabling the onboard processor and leaving the i2c bus available for access?

3) I want to add a date and time stamp to each event I log on the FRAM chip, I am thinking the best format would be UNIX or EPoC time as it will use only 4 bytes.  That way each event will use only 4 date/time bytes and one data byte and I can store a year’s worth of data on a 256k chip.  Is there a better way to store date and time?

Thank you all for your help,

Chip



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