Can I switch off the Atmega8U2 on the Arduino Mega2560 to save power?

Hi all,

Is there a possibility to switch off / disable the Atmega8U2 on the Mega2560 to save more power?

Background:
My Mega2560 uses about 60mA at 5V. When I go to power saving mode with Narcoleptic-library ( Google Code Archive - Long-term storage for Google Code Project Hosting. ) it still uses about 30mA. I have no idea which component consumes this 30mA if not the Atmega8U2 does?
Is there a possibility to switch off / disable the Atmega8U2 to save more power?

Thanks a lot for your help!

What leds are on? They can take quite a lot of current

That's close to what I found with the similar Uno board. I measured a minimum current consumption of 32mA, of which 6mA goes through the power LED and 5mA through the auto-reset circuitry. The remainder is mostly powering the 8U2 chip. What's needed is a Mega2560 version of the Arduino-Pro series, although I don't know if anybody makes such a board.

I wonder why the 8U2 doesn't take it's power directly from the USB port. Is there any reason for it to be powered when there is no USB connection present?

What are those jumpers near USB port for ??

There is only the power-LED on, but as tim7 wrote I also think that it uses only about 5mA. At least the LED connecet to pin 13 uses about 5mA if it's on.
By the way can I remove the power-LED without getting any problems? As far as I see it is only conneted to +5V, isn't it?

There's no problem with removing the power LED. If you're willing to modify the board, you could even cut the 5V power trace to the 8U2 chip and reattach it to the 5V pin on the USB connector. Looking at the PCB this appears eminently doable, but NB I have not tried it myself!

I've removed the power LED --> this saves about 3mA
I've also cut the pcb tracks to pin 4 (VCC) and pin 32 (AVCC) of the 8U2 (and connected them with an external switch to +5V) --> this saves about 15mA

So at last when the Mega2560 is in power saving mode and the power LED and the 8U2 are disconnectet the board still consumes 6.8mA.
This is tolerable when powering the board with battery, but still is not optimal.

I hope anybody has any idea how to save still more power...

What current drain is your goal?

... as little as possible :slight_smile:

I would be happy with 2mA. Then charging every month should be enougth

take a look at this http://www.sparkfun.com/tutorials/309 the atmega consumes only ~1uA in sleep mode

If you can't or don't want to use sleep mode, the next option to reduce current consumption is to run the processor at a lower clock speed and/or lower voltage.

The voltage regulator, even if not used, is going to consume orders of magnitude more current than the 328 in full sleep mode.

I know Seeeduino make a Arduino-Mega-alike, can't recall if it has power-saving features though (it does have switchable power source I believe). Maybe they do a Mega Pro ??

Please correct me if I'm wrong, but I think Narcoleptic-library ( Google Code Archive - Long-term storage for Google Code Project Hosting. ) sets the Mega2560 to sleep mode. So it should already use only µA's. Isn't it?

Have you any idea how much current the voltage regulator uses? And which part do you exactly mean? I don't use it. So should I remove it???

Yes, I know the Pro series, but as far as I've seen there is no Pro Mega2560. It would be nice indeed if anyone develops one. By then I've to help myself...

AFAIK the Seeduino has similar power regulation circuitry to the Arduinos, so probably consumes a similar amount of power.

Dogge, if you're reasonably well set-up for de-soldering and/or track-cutting you could try removing the 5V and 3.3V regulators and the power-switching circuitry. The regulators are the large 3-pin and smaller 5-pin parts on the board. The power-switching circuitry comprises the 8-pin op-amp and the small 3-pin FET.

If that's still insufficient you could go further and make the Arduino board into a bare-bones breakout board, stripping off everything except the Mega2560 chip, the resonator and the power decoupling capacitors. In this case you'd need an external USB-to-5V-serial converter for programming, as the Pro boards do.

Have you any idea how much current the voltage regulator uses? And which part do you exactly mean? I don't use it. So should I remove it???

A standard 7805 will waste several mA. (One manufacturers datasheet gives 6mA - that's 6000uA)

There are regulators that do significantly better (see this link » MCP1702 current draw » JeeLabs) But a regulator that isn't actually regulating can sink much more current than when it is regulating...

The schematics / layout for the board will show which is the regulator - I think different versions of the board may have different regulators and I doubt micropower was one of the requirements.

Desoldering it is risky unless you are confident about soldering/desoldering surface mount parts. I think a better approach for low power is to build a circuit from scratch or find an existing minimal board like the RBBB which you can populate with only the parts required. (I've built such a board for remote sensing and wireless sending and have its idle current down at about 10uA)

If you're prepared to solder the mcu yourself, you can buy just the Arduino mega pcb from e.g. WT588D-U WAV USB Voice Sound Module - emartee.com and fit only the parts you need.

The 2560 is a fine-pitch package, not really for hand soldering unless experienced and have hot-air rework station I think.

MarkT:
The 2560 is a fine-pitch package, not really for hand soldering unless experienced and have hot-air rework station I think.

True, but it can be done using a good soldering iron and a few accessories. There are lots of tutorials about this on the web, e.g. http://www.eetasia.com/ARTICLES/2003JUN/A/2003JUN19_ICD_HBM_AN.PDF?SOURCES=DOWNLOAD,

I don't think I'll be able to solder the Mega2560 on my one without buying a lot of things...

I think I'll try removing the regulator(s). I'll post the result...

MarkT did you bild a bord for the Mega2560?

No, only the 328 (well 168 actually, they are cheaper!)