Low Power Arduino Pro Mini running at 1Mhz

After playing with the MySensors¹ framework and possible sensor types, I build a prototype of a Temperature Sensor which is battery powered. The MySensors website contains a great guide on battery powered nodes² but I wanted to go one step further and reduce the clock of the used Arduino Pro Mini from 8Mhz to 1Mhz.

Jean-Matthieu DECHRISTÉ wrote an extensive article on this topic³, so this post only includes the basics.

Requirements

While you can use a simple USB-Serial adapter to program an Arduino, you’ll need an ISP to set the fused which are relevant for the clock. If you have a spare Arduino, you can simply use the Arduino ISP sketch and use it as programmer⁴.

Furthermore you need to calculate the fuses for the desired settings (e.g. using Fuse Calculator⁵).

If you want to keep the basic settings of the Arduino to default and only set the clock to 1Mhz and disable the brownout detection, you can use the following values:

Write Fuses with AVRDUDE

Depending on the used path and COM port, you might need to modify this command which writes the three fuses to the Arduino:

avrdude -Cavrdude.conf -v -patmega328p -cstk500v1 -PCOM7 -b19200 -U lfuse:w:0x62:m -U hfuse:w:0xda:m -U efuse:w:0xff:m

Program Board in Arduino IDE

After setting the fuses, you will no longer be able to use the default boards provided by the Arduino IDE to program your Arduino. I did not find a reliable way to program a 1Mhz Arduino using the USB-Serial Adapter, therefor it’s required to add a new Board Configuration to the IDE and use the ISP for further programming.

First find the boards.txt of your Arduino IDE installation. On windows it is placed in C:\Program Files (x86)\Arduino\hardware\arduino\avr. Now append the following configuration and save the file:

#############################################
########### Arduino Pro Mini 1Mhz ###########
#############################################

promini1MhzInt.name=Arduino Pro Mini (1MHz internal, 1.8V)
promini1MhzInt.upload.tool=avrdude
promini1MhzInt.build.board=AVR_PRO
promini1MhzInt.build.mcu=atmega328p
promini1MhzInt.build.f_cpu=1000000L
promini1MhzInt.build.core=arduino
promini1MhzInt.build.variant=eightanaloginputs

promini1MhzInt.menu.cpu.8MHzatmega328=ATmega328 (1.8V, 1Mhz)
promini1MhzInt.menu.cpu.8MHzatmega328.bootloader.low_fuses=0x62
promini1MhzInt.menu.cpu.8MHzatmega328.bootloader.high_fuses=0xDA
promini1MhzInt.menu.cpu.8MHzatmega328.bootloader.extended_fuses=0xFF

You should now see a new entry Arduino Pro Mini (1MHz internal, 1.8V) in your IDE.

Footnotes