I'm trying to power an Arduino Pro Mini 328 5V/16MHz with a single battery, preferably a LiFePO4 for safety purposes (it doesn't need to be more than around 300 mAh). However, I'm connecting a transceiver to the Arduino, and it requires 3.3V. This is the transceiver I'm using:


This is the Arduino Pro Mini I'm using:


My thoughts were to get maybe a 2S LiFePO4 battery, with nominal voltage at 6.4V, then use a linear voltage regulator to bring that 6.4V down to 5V to power the Arduino, then use another linear voltage regulator to bring the 5V down to 3.3V to power the transceiver. I fear that this may cause some damage somehow, as I'm not too experienced with voltage regulation. Will too much heat be produced? Is there a simpler way?

Any help would be greatly appreciated. Thank you!

  • 1
    \$\begingroup\$ Run your Arduino at 8 MHz or even better replace your ATmega-based Arduino with an ARM Cortex based solution (either running Arduino style software or not) which can operate at full speed at 3.3v or even lower supply. Chances are you can run this and the nrf radio at least down to 2.8 volts, maybe lower. \$\endgroup\$ – Chris Stratton Aug 24 '16 at 0:10
  • \$\begingroup\$ A fast approach is start with a board already designed to run on batteries, like this one: talk2.wisen.com.au/product-talk2-whisper-node-avr \$\endgroup\$ – Talk2 Sep 1 '16 at 4:31
  • \$\begingroup\$ I run Pro Mini's directly from LiPo batteries and have run them at 3V from a $0.78 buck regulator. You just connect the batteries directly to the 5V pin on the Arduino Pro Mini, bypassing the regulator. The Atmega328p datasheet suggests a 4MHz crystal would allow stability down to 1.8V, but I haven't had any problems with the stock 16MHz crystal at 3 - 4.2V. \$\endgroup\$ – Eisen Faust Mar 31 '17 at 9:11

6.4 -> 5V, then 5V -> 3.3V would be fine.

You may also consider dropping 6.4 -> 5V with one regulator, and 6.4 -> 3.3V with a second one.

The spec for the radio says 13mA, so
Power dissipated = 0.013A * (6.4-3.3) = 0.027 Watts,
which isn't much to worry about.

I can't think of anything to choose between the two approaches.

At these low-currents, you might even consider a DC-DC converter, stepping one battery up to 5V to drive the Arduino. Their are quite a lot of these around at modest cost for powering USB devices.

You might even feed one cell directly into the radio (maybe with a 3.6V zener protecting the radio).

I would be tempted to use a 3.3V Arduino and run it and the radio at 3.3V.

  • \$\begingroup\$ Thank you for your suggestions! Do you perchance have links to specific regulators you would recommend? Also, if I get a 3.3V Arduino Pro Mini, what kind of battery should I use to run it? If I want to use LiFePO4, the nominal voltage of 3.2V may not suffice? \$\endgroup\$ – theo1010 Aug 23 '16 at 21:32
  • \$\begingroup\$ I would choose a regulator by going to a distributor with a good search interface, and plug the values in. AFAIK, a LiFEPO4 will operate under 3V/Cell, so look for 6.0V -> 5V. You'd be looking for a 'Low Drop Out' regulator (LDO regulator) with a drop-out voltage around 0.7V or less. For 6V to 3.3V almost anything should work for the radio. For example mouser.com lets you specify the drop out voltage for LDO regulators. At a mimimum double the likely current you'll need. After that it very much depends on the type of package you can handle, if SMD are okay it's easy to find something. \$\endgroup\$ – gbulmer Aug 23 '16 at 21:56
  • \$\begingroup\$ I would need to check the circuit schematics, but I think that you could protect each voltage input on the Arduino and radio with a 3.3V zener and a small value series resistor, and feed the battery straight into the Arduino's 3.3V output. Last time I looked, the ATmega328P will run at 8MHz below 3.3V \$\endgroup\$ – gbulmer Aug 23 '16 at 21:59

No problem. It will work perfectly.

battery to 5V reg and 5V to 3v3 regulator.

5V reg : http://www.digikey.com/product-detail/en/texas-instruments/REG1117-5-2K5/296-27924-1-ND/2440705

3V3 reg: http://www.digikey.com/product-detail/en/texas-instruments/LM1117IMP-3.3-NOPB/LM1117IMP-3.3-NOPBCT-ND/483058

  • \$\begingroup\$ I'm thinking of using this regulator: link because of its low drop-out voltage. How would I wire this component? I don't understand what all of the pins mean. \$\endgroup\$ – theo1010 Aug 24 '16 at 18:19

I would either replace the reg on the Arduino board with a 3.3V reg and run both the Arduino and the nRF chip on 3.3V. And either change the Xtall to 8 or 10 MHz. Or just try ir at 16 MHz. I'd be surprised if it didn't run just fine.

Or if you use the LiFePO4 battery (Max 3.6 V), just run both the Arduino and the nRF chip directly from the battery. That should work quite ok, just out of the box. But you can't use a Li-ION battery the same way, as they can have over 4V on them. The nRF chip is rated to max 3.6 (might run on 4 V, but no guaranties.

Fora low energy application you should also investigate how to reduce the power consumption while running the program. Ie. by entering sleep mode whenever possible.

  • \$\begingroup\$ I'm assuming this is not for mass production, then you should read up on the datasheets a bit more. From the choice of boards I guess this is a one off hobby project. Some specifications can be bent a bit on projects like this. Maximum clock frequency and minimum voltage for the micro controller is one of the parameters one fairly safely can bend a little. \$\endgroup\$ – Bernie Nor Sep 23 '16 at 8:22

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