Arduino Pro Mini questions

Hi, everyone! I'm working on a two-pronged Bluetooth project: The first goal is to get the code working on an Arduino Uno; the second goal is to port the code to an Arduino Pro Mini 8MHz 3V3. I have two questions:

  1. To program the Pro Mini, I need an FTDI programmer. This mates to the 6 pin board header. Power goes IN through Vcc. When programming is done, I want connect a Bluetooth Mate to the 6 pin board header. In this configuration, does power flow OUT through Vcc into the Bluetooth module, assuming I have supplied power to Arduino's other Vcc or RAW pin?

  2. To power a 3V3 device, can I drive one pin HIGH to act as Vcc and one pin LOW to act as GND? I understand that this will only supply 40mA of current.

Many thanks :slight_smile:

~LU

  1. yes. From Raw, only 150mA is available. Less if the source voltage is really high.

  2. Yes, but not recommeded. Vout-low is only guaranteed to be 0.9V and Vout-high only guaranted to be ~2.3V to 2.5V with Vcc = 3.3V. Both will degrade as current increases above 20mA.
    40mA is absolute max and may cause damage long term ("long" undefined).
    Use a p-channel MOSFET and control it from an IO pin (low = on, high = off) instead.
    Find one with Low Rds and low enough Vgs to switch at 2.5V.

Thanks for the helpful reply.

With regard to point 2, if I supply unregulated voltage to RAW, will the second Vcc Pin (the one that’s not on the 6 pin header) supply regulated 3V3?