Theoros

Theoros

Theoros (Greek θεωρός): an official observer and envoy, sent to watch and report back.

USB-powered GPS logger with LoRa telemetry, built around the ESP32-S3.

Logs GPS fixes to a microSD card at 1 Hz, shows status on an OLED, and sends position over 866 MHz LoRa. WiFi provides NTP time, log download and OTA updates. Designed in KiCad as a 4-layer, fully machine-assembled board (Lion Circuits PCBA, Bangalore, single-sided).

Status: V1.0 design complete (schematic, routed PCB, fab outputs and firmware). Not yet fabricated or tested. Do not order boards from this repository until a tagged release exists.

Features

• ESP32-S3-WROOM-1-N8 with native USB (no USB-UART bridge)
• USB-C power and data, 5 V 1 A
• u-blox SAM-M10Q GNSS module with integrated antenna, UART and PPS
• microSD logging on a dedicated SPI bus
• RFM95W (SX1276) 868 MHz-band LoRa radio on a second SPI bus, u.FL antenna
• Telemetry and SD logs encrypted and authenticated (AES-128-CCM, per-tracker keys); separate tracker and receiver firmware
• Bare SSD1306 128x64 OLED panel on I2C, FPC connector
• Low-dropout 3.3 V linear regulator (AP7361C)
• Tag-Connect footprint for UART0 console, EN and GPIO0
• 4-layer stackup with solid ground plane; RF and USB traces checked at about 48 and 90 ohm on Lion's standard stackup

Block diagram

flowchart LR
    USB[USB-C] -->|VBUS| FUSE[Polyfuse 750 mA] --> LDO[AP7361C 3.3 V]
    USB <-->|D+ / D-| ESD[USBLC6-2] <--> MCU
    LDO -->|3V3| MCU[ESP32-S3-WROOM-1]
    MCU <-->|UART1| GPS[SAM-M10Q GNSS]
    MCU <-->|SPI2| SD[microSD]
    MCU <-->|SPI3| LORA[RFM95W 868] --> ANT[u.FL to SMA]
    MCU <-->|I2C| OLED[SSD1306 panel]

Repository layout

Documentation

• PCB design specification: pin assignment, power budget, layout rules and design decisions.
• Firmware (PDF): tracker and receiver firmware, build, console, WiFi service mode, OTA, bring-up.
• Security specification (PDF): threat model, AES-128-CCM design, key management, LoRa packet and log formats, provisioning, test vectors.

PDFs are generated from the Markdown with python3 docs/build_pdf.py.

Opening the design

Requires KiCad 10.0 or later. Open hardware/theoros.kicad_pro. All non-standard symbols, footprints and 3D models are in hardware/lib/, so no external libraries are needed.

Regulatory note

The LoRa radio is configured for 865–867 MHz, India's delicensed band. Users elsewhere must set the frequency, power and duty cycle allowed in their region.

License

Hardware design files are licensed under the CERN Open Hardware Licence Version 2 – Permissive (CERN-OHL-P-2.0). Firmware (firmware/) is licensed under the Apache License 2.0.