Arduino misconceptions 3: it isn’t low power enough to be run from battery

People build their projects, then want to battery power them. Their solution is to use a large battery (e.g. a 12V lead acid), connected to the Arduino external power input. The battery lasts mere days, and they become frustrated and move on to processors perceived as low power, like the MSP430 and ARM Cortex M0 series.

What if I said you could run a ATmega328P, RF transceiver and sensors from AA batteries for months at a time? A lot of people just won’t believe it, thinking the ATmega328P is a dated, power hungry chip that needs an ugly wall wart for power.

So why are people struggling with battery power?

1. The standard Arduino board accepts an external power input of between 7-12V, which then passes through a delightfully named NCP1117ST50T3G low dropout linear regulator to get it down to 5V for the rest of the board. If you are using a 12V battery via this regulator, and drawing a measly 50mA, you end up burning 0.35W of power in the regulator and the Arduino only using 0.25W! That linear regulator is an evil thing.

2. Most Arduino boards run at 5V. The ATmega328P runs fine at 3.3V and even down to 1.8V. At 3.3V, the chip uses ~40% of the power, and at 1.8V, it uses ~10%. Massive gains! 1.8V can make interfacing to other systems a bit awkward, but 3.3V is generally fine.

3. Most Arduino boards run at 16MHz by default, but a lot of the time you don’t need to run that quickly. By dropping to use the 1MHz internal oscillator, you reduce the power consumption 8 times. If you go further, you can use 128kHz oscillator and the power consumption drops 70 times!

4. A lot of Arduino code uses delays() and never sleeps. The ATmega328P has a sleep mode which can easily use less than 10µA – if you use an external 32.768kHz watch crystal, you can get this down to fractions of a µA. Learn about these and use them.

Where do you find out all of this info? It’s at the end of the ATmega328P datasheet.

You can workaround all of these – I thoroughly recommend reading JC Wippler’s posts on Jeelabs in his quest to reduce power consumption on Arduino-like board.

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