3.3V interfacing with 4.2V (x/post from project guidance)

Hi everyone,

For background here I’m using a 3.3V Arduino pro mini.

I recently came across a little module that I need to control, and it has a power up sequence where I must ground a pin on the module for >1s.

My idea was to try-state an Arduino pin, and then use it as a sink when I need to power-up the module.

The problem is that the module’s power logic gate is internally pulled up to the battery (4.2V), and I’m worried this may negatively effect the Arduino’s pin.

The module’s datasheet states that the power pin is internally pulled up to 4.2V via a 100K resistor, and that there’s also a 1K resistor between the logic gate, and the power pin input. (diagram 1)

So, I was hoping to bounce a few ideas off everyone here.

  1. Obviously, attaching the pin directly to the arduino is not the best solution. But would it create a problem? (diagram 2)
    It’s going to usually be left in the tri-state.

  2. Would putting a diode in between the power pin and the arduino pin solve this? (diagram 3)
    The forward voltage drop should not allow any quiescent current to flow while the pin is try-stated. When I ground the pin, current should flow to ground, correct?

  3. Obviously a transistor + resistor (diagram 4), is the best way to fix this; however, board space being at premium, I was hoping to take option 2.

TIA for any input :slight_smile:

diagram1.jpg

diagram2.jpg

diagram3.jpg

diagram4.jpg

Don't crosspost. It wastes time on everyone's part. Very few people will see your post here that won't see it over there.