Hello 
New to electronics, so please bear with.
I have a 3.3v Pro Mini I am using for a small bit of my Cosplay outfit I am making.
The Lipo battery I am using is 4.2v (actually 3.7v, but it is showing 4.2v on my tester).
How do I ensure only 3.3v ever reaches my Pro mini?
From what I have Googled... a voltage regulator won't work at such a low voltage.
Any suggestions?
Sas x
The Pro Mini has an onboard voltage regulator unless you are using the low power mode.
Takes 3.35 to 12v as board iput voltage. Specs .....
Ok.
If my battery runs down to say 3.3v however, will it not shutdown using the RAW pin?
My Lipo has protection down to 3v.
Need it to run for as long as possible!
The spec on the Sparkfun website says 3.4v min on the RAW pin.
Will the RAW pin regulator waste my battery life?
Sorry... still learning
Is there anything on a ProMini board that cannot operate normally at 5v?
And Atmega 328 must be run at 8MHz (rather than 16MHz) so that it can run on 3.3v but that does not preclude running it at 5v.
…R
Err... but I am not running at 5v?
My leds are set up for 3.3v operation and the sensor is also 3.3v max
SarahW2000:
The spec on the Sparkfun website says 3.4v min on the RAW pin.
That is the minimum voltage needed to keep the board running at 3.3volt (the regulator's ~0.1volt dropout).
But the board will keep on working if V-in drops well below that. 2.7volt should still be ok.
Question is what else you have connected to the ProMini.
That might not be happy with less than 3.3volt.
Leo..
Uhh use two batteries in series?? I doubt you'll have a problem incorporating that.
Probably the most simple solution.
SarahW2000:
Err… but I am not running at 5v?
My leds are set up for 3.3v operation and the sensor is also 3.3v max
Your Original Post just mentions the Pro Mini.
The Leds won’t care what voltage you use as long as the appropriate current limiting resistor is in place. Unless you are deliberately running them flat out from 3.3v then I reckon the existing resistors will be fine at 4.2v or even 5v.
You need to post a link to the datasheet or the sensor so we can see exactly what the specs are. Many things that are nominally 3.3v can actually take 3.6v or more.
…R
I have tried it using the RAW pin. Seems to be stable enough
Thank you for your advice
Sas x