POWER to the people.....<hrrrrm>.....ARDUINOS!

Projects General Guidance
1

Hi,

being a little unsure whether to put this posting into the "Electronics" thread or in this
one I decided for this one, since it is a very "close to Arduino" thing...
Hopefully this decision was OK...

I want to power my Arduino Pro Mini 3.3V 8MHz (this is a third party one made
by RobotDyn).
This particular ProMini has a 5 pin voltage regulator with a marking saying "LM33".
This in turn lead me to this item: MICREL 2507, which datasheet says, it is a efficient
linear voltage regulator with a low dropout voltage. I downloaded the datasheet from
the internet but I am unsure, whether it would be ok to reupload it here again...so better
not.

To my question:
I want a portable/mobile power source for my Pro Mini.
I am a little uncertain whether to risk LiPo Cells...a colleque burned down his
basement with one of these.
So better to stick with ordinary ENELOOP NiMH cells for now.
I activated the 2.7V BOD on my Pro Mini.
Possible setups

  1. 3x NiMH directly to the RAW pin
  2. 2x NiMH combined with a U1V11A made by Pololu:
    Pololu Adjustable Step-Up Voltage Regulator U1V11A.
  3. Some different efficient setup...

The ProMini with some sensors and a display will draw about 150mA for a short
time while displaying values. Most of the time it will display nothing and draw
roughly quessed 20-50mAh (unsure about this).

3x NiMH is the maximum setup. I dont want to carry more than this with me...

I know, that the BOD is quite useless with less than 3x NiMH and with the
step-up converter.

By the way: Is it allowed to measure the voltage of the power source with
an ADC pin which belongs to the powered MCU?
(I remember the instruction manual of a digital voltmeter which warns not to
measure the 9V battery while it is powering the voltmeter....)

What is the most efficient way to do such things and how can I circumvent the
BOD problem...?

Thank you very much in advance for any help!
Best regards,
mcc

2

3xNiMH yield 3.6V? Connect that to VCC pin, bypassing the regulator altogether.
8 MHz part will run fine up to 5V.
Will the other parts you have work at 3.6V okay? Check their specs.

I don't know if it's the Pololu 2560 (can't open their site at the moment), but they have a regulator that will run from a single cell even and provide power until the battery is down to 0.5V I think.
You can disable the brown out detector.
If you select "INTERNAL" for Aref use, it is 1.1 to 1.2V, you can then divide down the supply voltage into that range and use the ADC to make supply measurements.

3

Hi CrossRoads,

Thanks for your reply ! :slight_smile:

Freshly charged 3xNiMH yield 4.2 V...but not for such a long time ... :slight_smile:
Unfortunately I dont want to feed the sensors with such a high
voltage...they are all 3.3V based. Thats why I suggested the U1V11A
by Pololu -- it is the one you suggested.
I dont want to disable the BOD ... thats why I enabled it.

Nice to know that it will not harm the Pro Mini if I will directly measure
its power source with the ADC.

One question remains:
What is the most efficient way to power my setup from 2 or 3 NiMHs ?

Best regards,
mcc

4

Use the appropriate switching regulator if you want to maintain 3.3V.