Power Consumption

While searching the Internet for the auto-reboot solution, I came across a lot of low power Arduino projects. Given "coin battery" projects are the favour of the month, I though I would test the power consumption of the breadrino using the clock divide settiling.

Here is the test code:

/* Clock divide power consumption test */
void setup() {
  pinMode(LED_BUILTIN, OUTPUT);
}

void loop() {
  int i;

  // Signal start of loop
  cli();
  CLKPR=0x80;
  CLKPR=0;
  sei();
  digitalWrite(LED_BUILTIN,HIGH);
  delay(1000);
  digitalWrite(LED_BUILTIN,LOW);
  
  // Loop through Clock divides (1/1 to 1/256)
  for (i=0;i<=7;i++) {
    cli();
    CLKPR=0x80;
    CLKPR=i;
    sei();
    delay(8192>>i); // Enough time for the multimeter to settle
  }
}

Pretty simple, flash the builtin LED to signal the beginning of a loop and then progressively lower the clock speed. Hold the clock spped for about 8 seconds to allow the multimeter to settle.

Here are the results:

• 16 MHz    13.54 mA
•  8 MHz     9.26 mA
•  4 MHz     7.36 mA
•  2 MHz     5.76 mA
•  1 MHz      4.98 mA
• 500 kHz  4.53 mA
• 250 kHz  4.31 mA
•  125 kHz  4.20 mA

It looks like 1 MHz is a sweet spot for low power consumption using a 16 MHz crystal and no other power saving options.

Note: with a commerical Arduino board you probably have a power LED burning 5-10 mA on top of these reading (no wonder some people remove the power LED).

Slowing down the clock has other consequences. Off the top of my head: millis(), delay(), delayMicroseconds(), micros(), Serial, SPI, tone(), servo() etc. and any other timing related code will need to be adjusted. You can always adjust the code by going back to full clock speed for those sections of code.

However, there is generic board information and bootloader hex files available for 1 MHz operation on the Internet. Worth having a look!

Magic