Using low voltage to power a arduino chip

[RigorM]

Hi,

I need to build a project that will use 2xAA batteries to power a arduino atmega328p and a couple of leds.. most of the time the chip will be off (cut switch between the chip and batteries). and leds wont be on all that long.

Using the batteries, I would like the processor to work with a minimum of 2.7V and max 3.0V

I dont need the processor to be that fast.. 1-4Mhz would be just fine.

Trying to play with the fuse to set a lower freq and set the brownout at 2.7V

but can't seem to get it right.. the best I have so far is 1Mhz and its cutting a 3.2V


Anyone has some pointers ? this is driving me bonkers 

Thank !

J-F

[matseng]

If you don't need the full memory/code size of the 328 you might want to consider another AVR device. There are many that runs fine down to 1.8 volts and the ATtiny43U is perfectly happy with 0.7 volts.

[RigorM]

If you don't need the full memory/code size of the 328 you might want to consider another AVR device. There are many that runs fine down to 1.8 volts and the ATtiny43U is perfectly happy with 0.7 volts.

actually, I already have the chips in hand plus, I need all of its pins. :-)

Thanks anyway

[PeterFW]

but can't seem to get it right.. the best I have so far is 1Mhz and its cutting a 3.2V
Anyone has some pointers ? this is driving me bonkers 

I do not understand your problem, the datasheet says it should work at 2.7V, and a 328p works just fine at 3V at 8Mhz from personal experience.

Disable the BOD, you do not need that for LED blinky stuff, set the fuses for the right clock source and you are done.
The BOD will ensure proper operation at certain speeds, for blinking LEDs there is no need for a BOD.

Edit:
just to be shure, you are not using china arduino boards, right? They have voltage regulators on them, you do not want a voltage regulator.

[hneve]

The 328p works down to 1.8v if I'm not mistaken,  but you need to lower the frequency. Don't think it can do 16mhz at that voltage
Efuse 0xfd
Lfuse 0xe2
Hfuse 0xd9

This is what I think should work, not tested!!!

[RigorM]

but can't seem to get it right.. the best I have so far is 1Mhz and its cutting a 3.2V
Anyone has some pointers ? this is driving me bonkers 

I do not understand your problem, the datasheet says it should work at 2.7V, and a 328p works just fine at 3V at 8Mhz from personal experience.

Disable the BOD, you do not need that for LED blinky stuff, set the fuses for the right clock source and you are done.
The BOD will ensure proper operation at certain speeds, for blinking LEDs there is no need for a BOD.

Edit:
just to be shure, you are not using china arduino boards, right? They have voltage regulators on them, you do not want a voltage regulator.

I know that it should work at 2.7V thats the weird part.. but it doesn't brownout at that voltage.. much higher in fact.

I'm using a variable power supply with my fluke meter to simulate the batteries voltage.. I start at 5V and go down.. at 3.2xxxx its starts to give out..

i'll try to deactivate the BOD, thanks for the pointer. And as for the China board, nope, I only have the chip (TQFP32) on a breakout board to dip with a 16Mhz crystal and 2 18pF caps. the bare essentials for now.

Thanks !

[RigorM]

The 328p works down to 1.8v if I'm not mistaken,  but you need to lower the frequency. Don't think it can do 16mhz at that voltage
Efuse 0xfd
Lfuse 0xe2
Hfuse 0xd9

This is what I think should work, not tested!!!

I agree with you, It wont work at 16Mhz.. but again, I dont need to go that high.. like I said, a 1-4Mhz would be fine .. i'll take a look at your fuse settings.

Thanks !

[ralphd]

For low power you should run it off the internal rc oscillator.  You might get the external xtal to work at lower voltage if you dont't use full swing.

[RigorM]

For low power you should run it off the internal rc oscillator.  You might get the external xtal to work at lower voltage if you dont't use full swing.

Gotcha ! i'll remove the crystal and caps.. less parts is a good thing

[FreddyVictor]

For low power you should run it off the internal rc oscillator.  You might get the external xtal to work at lower voltage if you dont't use full swing.

Gotcha ! i'll remove the crystal and caps.. less parts is a good thing

seeing as you're a little new to this: you need to do is change the fuse to use internal 8MHz oscillator before removing the xtal

nb: you will not be able to connect to the chip if it doesn't have an active clock, so, if you remove the xtal before setting the fuse, then you won't be able to change the fuse ...

[RigorM]

For low power you should run it off the internal rc oscillator.  You might get the external xtal to work at lower voltage if you dont't use full swing.

Gotcha ! i'll remove the crystal and caps.. less parts is a good thing

seeing as you're a little new to this: you need to do is change the fuse to use internal 8MHz oscillator before removing the xtal

nb: you will not be able to connect to the chip if it doesn't have an active clock, so, if you remove the xtal before setting the fuse, then you won't be able to change the fuse ...

IM no stanger to this chip but never had to touch the fuses until a couple of days ago ;-)

but yeah, I think I came across that very problem at one time while flashing a sketch of bootloader ;-)

[TheWinterSnow]

This may not be exactly what you asked for, but this is what I would personally do.

If you don't have any 3.3v sensitive devices plugged into your MPU, how about a 3.3v/5v regulated boost converter such as the MCP1252?  If you are worried about low power and long battery life, you can still run the clock lower?   

If you are worried about low battery causing performance issues, if you do go the DC-DC boost solution mentioned above, a low battery indicator can let you know when you need to change batteries while the supplied voltage to the MPU remains unchanged until the boost chip drops out.  You can set a voltage comparator to cut power to the MPU if the voltage drops below a certain threshold.

[linux-works]

fwiw, I just learned that the 328 chip can run fine down to 2.8v on the 16mhz resonator and NOT need any special bootloader or fuses.  surprised me quite a bit.  I'm trying to make a handheld remote using a 328 chip and hoping to use 3.7v lipos on it.  during a psu test, I lowered voltage until the serial port (that I need) stopped working.  that happend right about 2.75v.  so, 3.3v is more than fine for the standard arduino.

I have not tested 100% of the chip yet but the things I use, serial and i2c plus simple digital reads and writes all work fine at 3v using standard bootloader.

you don't want to go thru a voltage regulator as that drops some voltage.  I'm using a bare 328 chip, resonator and nothing else on my own diy arduino board.

[amyk]

Read datasheet. It's all in there.

[george graves]

Read datasheet. It's all in there.

LOL.