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Topic: Power Arduino Micro via 3.7V Lithium Polymer (Read 2024 times) previous topic - next topic

ycans

Hello,

I have a 3.7V Battery that I wish to power a Micro via a step up DC-DC circuit to convert the 3.7V to 5V.
However, reading the summary, the recommended input voltage is 7-12V
http://arduino.cc/en/Main/arduinoBoardMicro

Has anyone does something like this before? I was thinking of putting two batteries in series to get 7.4V, but then wondered what affect that would have on a standard charging circuit, such as this: https://www.sparkfun.com/products/11231

Any thoughts? Thanks

michinyon

To supply the arduino,   you can  (a) supply 5V directly to it,   or you can (b) supply 7-12 Volts to the voltage regulator on the arduino.   The voltage regulator consumes some volts,    so if you supply less than 7 volts to the voltage regulator,   then it's output will be less than 5 volts.

If your 5V supply is reliable,   you don't need the regulator,  you can supply 5V directly,  that should work fine.

jremington

For your situation I would recommend using a single 3.7V battery (use an appropriate charger) and a very efficient step up regulator similar to this one: http://www.pololu.com/product/2562 and power the Arduino at the 5V input.
The on-board regulator is very inefficient.

ycans

Thanks for your help!

On a slightly different note, I am awkward for space, but want a longer battery life, so do you see any problems with using two lipo cells and parelleling them together? I am going to be using this charger https://www.sparkfun.com/products/11231

Thanks

jremington

I've successfully used LiPo batteries in parallel, but they should be of the same age and capacity (in mAh or Ah) and always in parallel, for both charge and discharge cycles. Otherwise the charge profile will not be correct for one battery and then, you might be in a dangerous situation.

nixiebunny

I have one of these Micro boards and I'm very interested in powering it from a 3.7V LiPo cell also. I've looked at the schematic diagram, and I don't see any reason that it won't work from 3.7V. The processor is specified to work down to 2.7V, and it's the only chip on the board!

Am I missing something?

(I'm an engineer with decades of experience using microcontrollers, so I need no coddling.)

CrossRoads

32U4 chip is only spec'ed for 16 MHz operation at 4.5V and above.
3.7 is below that. By a lot. See
29.5 Maximum speed vs. VCC
in the datasheet. You might get erratic  operation running below spec - we saw that here recently with a 1284P chip that had serial issues until the Vcc was brought up to spec.
http://www.atmel.com/products/microcontrollers/avr/megaAVR.aspx
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

MarkT


I have one of these Micro boards and I'm very interested in powering it from a 3.7V LiPo cell also. I've looked at the schematic diagram, and I don't see any reason that it won't work from 3.7V. The processor is specified to work down to 2.7V, and it's the only chip on the board!

Am I missing something?

(I'm an engineer with decades of experience using microcontrollers, so I need no coddling.)


Its a USB chip, USB is 5V only.
[ I won't respond to messages, use the forum please ]

CrossRoads

USB is not 5V only. Read the datasheet, Section 21:

To comply with the USB Electrical specification, USB buffers (D+ or D-) should be powered
within the 3.0 to 3.6V range. As ATmega16U4/ATmega32U4 can be powered up to 5.5V, an internal regulator provides the USB buffers power supply.

Figure 21-2 then shows the Operating modes vs frequency & power supply.
3.7V operation at 8 MHz with USB port powered via internal regulator is perfectly fine.
4.5V is needed for 16 MHz operation as noted earlier.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

nixiebunny

Thanks for the info on the frequency vs voltage restriction. That useful fact is not mentioned in the 32U4 chip summary.

I guess I'll have to use a stinkin' boost converter to run the thing from one lipo cell. Drat!

CrossRoads

Pololu makes some, very little boards.
http://www.pololu.com/category/132/step-up-voltage-regulators
Test with one to start, one with autocutoff if voltage goes too low so you don't kill the battery by overdischarging.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

nixiebunny

Thanks. I have ordered a couple step-up boards to play with.

I also started a thread on designing the Arduino Micro that I really want, which can charge a LiPo battery and has the step-up built in. My threshold for new circuit board designs is pretty low, and I think there's a market for it.

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