I have a battery powered bare bones Arduino. After reading the power saving methods article from gammon.com.au, I'm a little confused still about how much power an external oscillator consumes.
This is the article:
By changing the fuse bits the processor can run on its 8 MHz internal clock. Running Sketch A above, with lfuse set to 0xE2, the board consumed 11.05 mA (compared to 15.15 mA using the crystal).
Does that mean the processor running at 16MHz uses an additional 4mA current compared to 8MHz? How much of that additional 4mA is due to powering the external crystal? Should I even be worry about the power consumption due to external crystal, or is that silly?
I'm just looking to run the Arduino for 6 months on 3xAA batteries.
It is more likely have to do with the 16MHz versus the 8MHz.
That doesn't matter a lot, if the chip is in sleep mode for 99% of the time.
Do you want to have it running continuously for 6 months ? that is not possible.
Caltoa:
It is more likely have to do with the 16MHz versus the 8MHz.
That doesn't matter a lot, if the chip is in sleep mode for 99% of the time.
Do you want to have it running continuously for 6 months ? that is not possible.
Oh ok, that's what I was hoping. The chip will be sleeping for 99.9% of the time.
If you design it careful, you can have it running for maybe 2 years.
This is sleep library that shuts down the complete chip and only uses the watchdog to wake up: http://code.google.com/p/narcoleptic/
You can use it for example to transmit the temperature wireless every 5 minutes.
Does that mean the processor running at 16MHz uses an additional 4mA current compared to 8MHz? How much of that additional 4mA is due to powering the external crystal? Should I even be worry about the power consumption due to external crystal, or is that silly?
An AVR chip inherently draws more current the faster you clock it, regardless of the clock source. Another way of saying that is that there should be no appreciable difference of current draw from using the internal 8 Mhz R/C clock or an external 8 Mhz crystal resonator. There are graphs in the AVR datasheet showing the relationship of chip current draw Vs clock speed
Caltoa:
It is more likely have to do with the 16MHz versus the 8MHz.
That doesn't matter a lot, if the chip is in sleep mode for 99% of the time.
Do you want to have it running continuously for 6 months ? that is not possible.
Oh ok, that's what I was hoping. The chip will be sleeping for 99.9% of the time.
Furthermore if the time awake is shorter with a faster clock it may be more energy efficient to run at 16MHz since the total charge flowing
through the process would be about the same, but any peripheral chips
may be powered up for a shorter period too... You also have to factor
in crystal start-up time and suchlike to make such an analysis.