A battery powered Mysensors node from an Arduino Pro Mini clone

10 Sep 2018

It is not very difficult to build a reasonably nice MySensors node based on very affordable hardware. This is a reminder for myself in order to be able to reproduce one.

A basic battery powered Mysensors node

Based on: the documentation by MySensors and a 3.3V 8MHz Arduino (clone) Pro Mini from the usual sources (Banggood, AliExpress).

Handy pinout guide

Perform the hardware mods from above link:

Disable power LED (either remove it or the resistor next to it).
Remove voltage regulator (in this case I linked the in & out pins to be able to power through the RAW pin.

Make an Arduino ISP programmer

In order to reflash the bootloader, we need an In-System Programmer (ISP). It is possible to use another Arduino as the ISP, and I like to use another Pro Mini.

Hardware

I follow the following schematic: Fritzing schematic of Pro Mini ISP

And in reality on a breadboard, it looks like this (with a LED added to pin 9):

Breadboard Pro Mini ISP

Flash the ISP firmware

Start the Arduino IDE
Open ArduinoISP sketch from the repository
Connect the ISP using a USB-serial connection
Select board Arduino Pro or Pro Mini
Flash the sketch.

Install boot loader:

In order to get a lower Brown Out voltage, we need to flash a new bootloader. Actually that’s not strictly required, but it’s the easiest way. I am using Optiboot bootloaders compiled by Gert Sanders, so many thanks to him.

Unpack rar in Various-bootloader-files-based-on-Optiboot-62
Move folder atmega328p to Arduino.app/Contents/Java/hardware (this is the OS X location)
Start Arduino.app
Select Tools->Board->atmega328p based - 32 pin TQFP
Select 8MHz - crystal - 38K4 - D13
Select Brown out detection - 1V8
Select correct USB port
Select Programmer: "Arduino as ISP"
Tools->Burn Bootloader

Test

Connect the board to the USB serial adapter (disconnect the ISP)
Upload example Blink
Upload Blink with modified timings
I also like to try the ASCIITable example
Quit the Arduino IDE

Upload the real script

I use platformio to run my projects, so uploading is pretty easy:

Switch to the project folder
Edit baud rates in the platformio.ini. I use 38400 for upload and 9600 for monitor.
pio run -t upload or if you want a debug monitor: pio run -t upload -t monitor