Field notes on Scott Penrose - Embedded Systems & Software Consultant, Melbourne

The RockBLOCK 9704 on Zephyr, and the pin wired upside down

Mon, 26 Oct 2026 09:00:00 +1100

A microcontroller on my back step sent 16 bytes through an Iridium satellite. The message was “Stamp-C3 says hi”, and it was in Cloudloop about ten seconds after the shell command that sent it. The Zephyr module that got it there is now public: rockblock9704-zephyr, MIT.

Why this modem

The modem is Ground Control’s RockBLOCK 9704, the Iridium Certus one. I have put about 70 of its older cousins, the 9602 and 9603, into Antarctic wave buoys since 2012. Those carry 340 bytes a message, so a buoy has to reduce a whole wave record to statistics on board before anything leaves. That has worked, and the science has always run on the statistics.

I built a LoRa analyser because I was sick of guessing

Fri, 04 Sep 2026 12:30:00 +1000

Debugging a LoRa link used to go like this. A node stops reporting, so I swap the antenna, move the gateway and drop the spreading factor. Something improves, or it doesn’t, and I have no idea why, because I cannot see the band.

So I built the thing I kept wishing I had. LoRaScope is a small radio that listens to the band and shows what is on the air: LoRa, MeshCore and LoRaWAN, with live switching between them. There is no gateway or network server in the path. The radio receives the packet, the box decodes it, and it shows up on a screen.

Zephyr is the DOS-to-Linux moment for embedded

Sun, 16 Aug 2026 00:10:00 +1000

I’ve written embedded firmware for a long time, on AVR, ESP32, nRF52 and RP2040, and mostly the default was bare metal or a small superloop. It worked. It was also the DOS era of microcontrollers: you own the whole machine, you write every driver yourself, and scaling up means more #ifdef blocks. FreeRTOS if the project was bigger, but the same shape.

Zephyr is the move to Linux. It brings what Linux got right down to a 64KB MCU.

We open-sourced our Antarctic wave buoys

Fri, 03 Jul 2026 00:00:00 +0000

For over a decade I built and maintained the firmware for the Waves In Ice buoys, instruments that are placed on Antarctic sea ice, freeze in, and report wave motion back over Iridium satellite for months at a time. The data from the earlier generations contributed to peer-reviewed science, including a 2014 paper in Nature on storm-induced sea-ice breakup.

That work is now open source as WII5 at wii5.sh3d.com.au: AVR firmware, schematics, PCB designs, enclosure notes, the on-board wave-statistics mathematics, and deployment logs going back to 2012.