High power consumption by the 8U2 USB interface in sleep mode

Hi I'm building a project that will use an Arduino Mega running on batteries and it will be using sleep mode to reduce power consumption - set_sleep_mode(SLEEP_MODE_PWR_DOWN); - to reduce the system power consumption. I've noticed that the Mega 2560 uses quite a bit more power when I put it to sleep, than does a Mega 1280 - 30 mamps vs. 17 mamps. Further, a similar difference also occurs in the power consumption of a sleeping UNO when compared the Duemilanove - 32 maps asleep vs. 15 mamps. Those numbers are for a bare Arduino with an Adafruit Data Logger shield (SD card and real time clock) running from an external power supply (and the USB cable disconnected).

I presume the two newer boards (2560 and UNO) have higher sleeping power consumption because the new 8U2 controller for the USB uses a lot more power than the FTDI chip. Given that the 8U2 controller is programmable, is there any way to put the USB system to sleep? Since I need to use the USB to talk to the instrument periodically, I'd have to be able to wake the 8U2 up periodically to check for incoming comms. Maybe have the USB run on a reduced duty cycle of listening for comms 10 seconds of every 2 minutes, or such.

Any advice would be appreciated. I'd like to minimize the sleeping power drain, as a 1280 in sleep mode uses about 20% of my power budget, but that goes to 40% with a 2560 and really starts to impact my operating lifetime (unless I just throw more batteries in, which is the fall back plan).

Thanks for any input.

Ken Johnson

hi, I have same problem with same board and shield. I think that only way is cut acc :D little bit ultimate solution.

So, this is not solution I try it and it does not work. another way?

Hi Ken,

I think if you are going for a real low power consumption board you have to build one yourself. 30mA is a lot if you want to drive the board with rechargeable batteries. You may have to investigate which part needs how many energy to get a real thriving system.

For example if you use the MC33269D you have 5 to 20mA (according to datasheet) quiescent current (fixed output). Because you are using minimum 5 rechargeable batteries (1 Volt droput from the voltage regulator so 5 batteries might be the minimum) there is a lot of energy vaporating.

You wrote that you have a USB-connection to an "instrument". Why can't you use the energy source from that device?