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Telemetrium

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Telemetrium is a dual-band, full-duplex LoRa telemetry board built around two independent Semtech LR1121 transceivers. With dedicated external PAs, calculated RX matching networks, dedicated baluns, and harmonic LPFs on both bands, it delivers +27 dBm on Sub-GHz and +22 dBm on 2.4 GHz simultaneously — enabling true full-duplex operation over long range.

Features

  • 2× Semtech LR1121 — dual-band transceivers (Sub-GHz + 2.4 GHz), one per channel
  • True full-duplex — LR1121_1 TX while LR1121_2 RX, and vice versa
  • Sub-GHz band: SKY66423-11 FEM, +27 dBm output, DEA100915LT-6319A1 LPF
  • 2.4 GHz band: RFX2401C FEM, +22 dBm output, DLF162500LT-5028A1 LPF
  • SKY13453-385LF SP2T RF switch per transceiver for antenna routing
  • HHM1932A2 differential Sub-GHz RX balun (per transceiver)
  • Calculated RX and RFO port matching networks (Smith chart optimized, VSWR 1.06 @ 868 MHz)
  • 3rd harmonic notch filter on Sub-GHz RFO path
  • 32 MHz TCXO (±2 ppm, X1G004131004212) per transceiver
  • Microcontroller: STM32G474CCT6
  • USB-C with ESD protection (TPD4E001) and TPS2116 power mux (USB / JST-GH)
  • JST-GH 4-pin UART header (TX, RX, 5V, GND)
  • SWD debug header (6-pin, 1.27mm)
  • WS2812B ARGB LED
  • BOOT0 / NRST tactile buttons
  • 3.3V buck (AP63200WU-7) from 5V input
  • 2× SMA edge connectors (one per transceiver)

Hardware

Microcontroller: STM32G474CCT6

  • 32-bit Arm® Cortex®-M4 with FPU
  • Up to 170 MHz CPU frequency
  • 512 kB Flash, 128 kB SRAM
  • SPI1 → LR1121_1 (NSS, SCK, MISO, MOSI, BUSY, IRQ, RST)
  • SPI2 → LR1121_2 (NSS, SCK, MISO, MOSI, BUSY, IRQ, RST)
  • USART1 → JST-GH UART header
  • Debug: SWD, SWO
  • Package: LQFP-48

Transceiver: Semtech LR1121 (×2)

  • Dual-band: Sub-GHz (150–960 MHz) + 2.4 GHz (2.4–2.5 GHz) simultaneously
  • LoRa, (G)FSK, BPSK modulation
  • Integrated PA, LNA, and frequency synthesizer
  • RFO_HP_LF port used for Sub-GHz TX (external PA chain)
  • RFI_N/P_LF0 differential port used for Sub-GHz RX (balun + matching network)
  • RFIO_HF port used for 2.4 GHz (external FEM)
  • 32 MHz VTCXO reference (±2 ppm)
  • SPI interface, up to 16 MHz
  • Package: QFN-33

Sub-GHz Front End (per transceiver): SKY66423-11

  • +27 dBm TX output power
  • Integrated PA + LNA
  • CPS / CTX logic control from STM32
  • Harmonic filter: DEA100915LT-6319A1 Sub-GHz LPF
  • Differential RX input via HHM1932A2 balun

2.4 GHz Front End (per transceiver): RFX2401C

  • +22 dBm TX output power
  • Integrated PA + LNA
  • TXEN / RXEN logic control from STM32
  • Harmonic filter: DLF162500LT-5028A1 2.4 GHz LPF
  • DC blocking on RFIO_HF path

RF Switch (per transceiver): SKY13453-385LF

  • SP2T — routes Sub-GHz or 2.4 GHz path to shared SMA antenna
  • VCTL logic control from STM32 (SW4 signal)
  • +3V3 biased

RX Matching Network (Sub-GHz, per transceiver)

  • Input impedance from LR1121 RFI port: Z = 9.40 Ω − 141j Ω
  • Matching to 50 Ω via L-network: 22 nH series + 5 nH shunt (Smith chart optimized)
  • Final impedance: 46.98 − 0.31j Ω (VSWR 1.06 @ 868 MHz)
  • Insertion loss: < 0.005 dB (S21 max −0.003 dB)
  • Tolerance: 3% on both inductors

Power Architecture

  • Input: 5V via USB-C or JST-GH connector
  • Power mux: TPS2116DRLR — prioritizes JST-GH 5V, falls back to USB VBUS automatically
  • 3.3V rail: AP63200WU-7 buck converter, powers MCU and all RF circuitry
  • USB-C ESD: TPD4E001RDBVR TVS on D+/D−
  • USB-C CC: 5.1 kΩ pull-downs (UFP/sink)

Headers & Connectors

Connector Type Signals
UART / Power SM04B-GHS-TB +5V, GND, RX1, TX1
USB-C USB4105-GF-A USB FS D+/D−, VBUS, CC1/CC2
SMA 1 CON-SMA-EDGE-S Antenna — Transceiver 1
SMA 2 CON-SMA-EDGE-S Antenna — Transceiver 2
SWD 6-pin pad (1.27mm) VCC, NRST, GND, SWO, SWCLK, SWDIO

Schematics / PCB / 3D

Keybinds

  • Select LMB
  • Zoom In/Out Scroll
  • Pan RMB Drag
  • Reset View R

Quick start

  1. Connect 5V via USB-C or JST-GH header
  2. Connect antennas to both SMA connectors before applying power — never TX without antenna
  3. Flash firmware via USB DFU or SWD header (STM32CubeIDE / OpenOCD)
  4. Connect UART header to your flight controller or telemetry host (TX→RX, RX→TX)
  5. Configure LR1121 band, spreading factor, and channel assignment in firmware

Safety

  • Never transmit without antennas connected — the external PAs can be damaged by open-load TX
  • +27 dBm / +22 dBm output is significant RF power — maintain safe distance from antennas during testing
  • Do not connect both SMA ports to the same antenna — the two transceivers operate independently and simultaneously
  • Sub-GHz and 2.4 GHz share a single SMA per transceiver via RF switch — the firmware must correctly assert RFSW_ANT before any TX/RX operation
  • USB and JST-GH 5V can be connected simultaneously — TPS2116 power mux handles priority automatically

🔜 Firmware

Board is being manufactured — firmware examples and configuration guides coming soon.

Photos

Downloads

Telemetrium.zip 

git clone https://github.com/sanko0112/Telemetrium.git
cd Telemetrium