power

Arduino at 5volts and 5.3mA, and a Surprise

Submitted by Ed_B on Fri, 02/04/2011 - 04:18

An ATmega168 Lilypad Arduino is the basis for a set of design experiments for a larger project. The larger project is not described here. Power consumption is an issue, so I set about trying strategies to reduce Arduino power consumption. As  basis of comparison, measurements were made based on settings that could be changed in a running program, not fuses or circuit adjustments. I set out to get three or four baseline numbers relating to clock speed and internal peripherals. There was a big surprise hiding under a rock: The Arduino-like circuit being tested had by default, active, open input lines that drastically increased the mcu power consumption. The open lines also caused the chip power consumption to fluctuate sporadically on its own, and the fluctuations became more extreme as I moved my hand around the board. It took me a while to notice the correlation between my hand position and the current draw on the mcu, but then the mystery was gone. This is a classic case of the old caveat about not leaving cmos input pins floating -- tie 'em high, or tie 'em low, but don't leave 'em open. In the MCU, two things will fix this in software: set the pin to output, or leave it as input and turn on its internal pullup resistor. 

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