mochiRadio 📡

A coin-cell-powered 915 MHz wireless sensor node — an ATmega328P driving a Silicon Labs Si4455 sub-GHz transceiver, with onboard sensing and a hand-tuned RF matching network. Designed end-to-end in KiCad: schematic → impedance-matched RF front-end → PCB layout.

What it is

CoinCellSensor is a tiny battery-powered telemetry board: it wakes, samples its sensors, transmits a packet over the 915 MHz ISM band, and drops back to sleep to sip coin-cell power.

MCU	ATmega328P
Radio	Silicon Labs Si4455 (EZRadio sub-GHz transceiver, 915 MHz ISM)
Sensing	onboard temperature + pressure, status LED
Power	single coin cell, low-power duty-cycled operation
EDA	KiCad — schematic + PCB layout

The RF front-end (the part I care about most)

The Si4455 only hits its range and efficiency with a properly impedance-matched front-end. I implemented the direct-tie matching + harmonic-filter topology between the radio and the antenna:

Choosing the L/C values, keeping the RF trace controlled-impedance, and getting the ground return right is the same class of problem I now work on at scale (RF coexistence and antenna de-sense). This board is where that started.

Build photos

📷 Photos of the assembled board are coming — drop them in Images/ and they'll slot in here.

Repo contents

• CoinCellSensor.sch — full schematic
• CoinCellSensor.kicad_pcb — PCB layout
• *.lib / *.net / *.pro — KiCad symbol libraries, netlist, project files

Things I'd change in a rev 2

• Move to a fully SMD, tighter 2-layer stackup
• Add a u.FL / RF test point for bring-up measurements
• Modern low-power MCU with an integrated sub-GHz radio

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Built by Frank Walsh — electrical engineer (RF / PCB / embedded).