Low-Power Cellular IoT with Jared Wolff of Circuit Dojo

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In this episode, Cliff talks with Jared Wolff, founder of Circuit Dojo and an expert in low-power, cellular-connected microcontroller systems. We cover the Nordic nRF9151, battery-powered LTE-M and NB-IoT design, satellite connectivity, Zephyr RTOS, and building a self-hosted IoT server in Rust.

• Jared's path: from taking apart computers and a first Arduino, to hardware validation on the iPod team at Apple and at Cisco, to Bay Area startups and consulting in Connecticut.
• Circuit Dojo makes the nRF9160 Feather and the nRF9151 Feather, compact Feather boards supporting LTE-M, NB-IoT, and non-terrestrial networks, at about a fifth of the size of Nordic's development kits.
• The nRF9151 is a pre-certified system-in-package with a modem CPU and an application CPU. It has enough resources to run a full IoT application, which keeps OTA updates simple.
• The nRF91 as a PPP modem for an OpenWrt router, paired with an nRF52840 running as a Thread radio to build a Thread border router. Linux handles the NAT64 and IPv6 work that is hard to fit on a microcontroller.
• Low-power design lessons:
  • Know what every part does when the system is powered down; prove out power switching on development kits before the first spin.
  • Give real-time clock chips their own power domain and isolate them carefully.
  • Hunt phantom current with the Nordic Power Profiler Kit or a Joulescope; watch the nRF52 NFC pins.
  • The nPM1300 PMIC ship mode reaches nanoamps; active standby with a cellular connection is about 4–5 µA.
  • Zephyr handles much of the peripheral power management for you.
• Reliable cellular is mostly about connectivity logic: handling marginal signal, relocation, and underground installs gracefully. Site surveys matter; one install had to move from LTE to Ethernet.
• Satellite (NTN) on the nRF9151 with Skylo and Myriota, using an NTN-enabled Soracom SIM, for low-bandwidth messaging or CoAP over UDP in remote locations.
• Other radios: Wi-Fi HaLow (802.11ah) for long-range links, LoRa, and DECT NR+, which needs separate proprietary modem firmware.
• Zephyr RTOS: a steep start, then "batteries included." Claude Code handles Zephyr well with the kernel and HAL sources in the West workspace. Jared's YouTube channel has many Zephyr tutorials and live streams.
• Lion, Jared's upcoming self-hosted IoT server: a single Rust binary with OTA and data handling, using CoAP over DTLS with CBOR (an approach inspired by Golioth), plus a Zephyr client library. Getting server-side DTLS working in Rust was the hardest piece.
• AI in hardware: a Claude skill for GitPLM Parts library work that pulls datasheets and creates KiCad symbols and footprints.
• Tool recommendation: a Prusa 3D printer. Jared prints test and programming fixtures with pogo pins in-house, in place of machined fixtures that cost $500 to several thousand dollars.
• Advice for young engineers: learn on your own, build and break things, study existing reference designs, and then add your own improvements.

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