Reducing Arduino Power Consumption
Contributors:
Alex the Giant
Alex the Giant 
Resources and Going Further
More information on low-power modes and options can be found in the datasheet for the 328P.
For more power-related fun, check out the following SparkFun tutorials.
Uh-Oh Battery Level Indicator Hookup Guide
Learn how to assemble and use the TL431 in the Uh-Oh Battery Level Indicator Kit.
PicoBuck Hookup Guide v12
The PicoBuck board is a high-efficiency three-channel constant-current LED driver.
Blynk Board Project Guide
A series of Blynk projects you can set up on the Blynk Board without ever re-programming it.
IoT Power Relay
Using the ESP32 to make a web-configured timed relay.