Project Firefly Board Overview

flux

2:03

Project Overview: Firefly Board
Purpose
The Firefly Board is an IoT node for wireless control of lighting, water valves, and other home automation elements in areas without GSM or Wi-Fi. It uses LoRa for long-range, low-power communication and supports battery operation with USB-C charging.
1. Core Functional Blocks 
Diagram



  
    
  
  
    
  












SPI

GPIO

SWD

ADC










“Power Management”
“Processing Unit\nSTM32G0”
“LoRa Radio Module”
“Battery Charger”
“3.3V LDO Regulator”
“Status LED”
“I/O Interfaces\nHeaders & USB”
“Li-Ion Battery”
“SWD Header”
“Battery Voltage Divider”

2. Component Summary

RoleDesignatorPart & Link
MicrocontrollerU1U1
LoRa Radio ModuleU2U2
Battery Charger ICIC1IC1
3.3 V RegulatorU3U3
USB-C Power ConnectorJ4J4
Battery ConnectorJ1J1
Programming HeaderJ3J3
GPIO ConnectorJ2J2
Status LEDLED1LED1
Reset Pull-upR3R3 – 100 kΩ
LED Current-limitR2R2 – 470 Ω
Battery-ADC DividerR4, R5R4, R5 – 100 kΩ each
Decoupling CapacitorsC1, C2, C3, C4, C5, C6, C7, C8C1, … C8 – 0.1–10 µF (0603)
3. Design & Implementation
  1. Power Input & Management
    • USB-C (J4) accepts 5 V.
    • Charger IC: @IC1 manages Li-ion charging.
      • Charge current set by R1 (2.2 kΩ → ~100 mA).
    • Battery Rail: VBAT feeds both the MCU and the 3.3 V regulator.
    • 3.3 V LDO: @U3 supplies clean 3.3 V for logic.
    • Decoupling: Each power pin has a 0.1 µF cap ([C6], [C4], [C5]) plus bulk 4.7 µF caps ([C3], [C2], [C1], [C7], [C8]) in 0603.
  2. Battery Monitoring
    • Divider [R4]/[R5] scales VBAT to ADC range.
    • MCU measures VBAT via VBAT_ADC net for charge management and low-battery alerts.
  3. Processing & Communication
    • MCU: @U1 (ARM® Cortex®-M0+, 64 MHz, 32 kB Flash).
    • LoRa Module: @U2 connected via SPI1 (MOSI/MISO/SCK/NSS) + RESET + DIO0 for interrupts.
    • Debug: SWCLK/SWDIO header ([J3] pins 3–4) for programming and firmware updates.
    • Boot-Mode: BOOT0 strapped by net portal and reset pull-up ([R3]).
  4. User Interface & I/O
    • Status LED: [LED1] driven through [R2] to indicate power, charging, or radio activity.
    • GPIO: 2-pin socket (J2) and 4-pin header (J3) expose extra pins for sensors or actuators.

4. Key Design Choices & Trade-Offs

DecisionTrade-Off / Benefit
STM32G0 MCULow-power, cost-effective vs. limited Flash (32 kB)
Off-the-shelf LoRa moduleSimplifies RF design vs. slightly larger footprint & cost
SOT-23 Li-ion chargerCompact vs. limited charge current (~100 mA)
0603 passivesSmall footprint vs. more challenging hand-soldering for prototyping
USB-C power onlyModern interface vs. no upstream data capability (host-only power input)
5. Performance & Challenges
  • RF Layout:
    • Antenna clearance around [U2] must avoid ground pour for optimal sensitivity.
    • Matching network omitted—module includes on-board filter but keep keep-out.
  • Power Efficiency:
    • Sleep Modes on MCU and LoRa reduce consumption (<10 µA).
    • Charger quiescent (~2 µA) vs. specialized PMICs with lower standby.
  • Thermal / Current:
    • LDO rated 600 mA; design draws ~20–50 mA typical.
    • Trace widths ~0.25 mm (Top) support up to ~500 mA with margin.
6. Real-World Applications
  • Smart Lighting: Battery-powered light switches deep in buildings.
  • Agricultural Sensors: Soil moisture transmitters in remote fields.
  • Utility Control: Valve actuators for water lines beyond Wi-Fi range.
7. Improvements & Future Enhancements
  • External Flash for logging when out of range.
  • Sensor Integration: Add I²C port for environmental sensors.
  • Solar Charging: Replace SOT-23 charger with MPPT capable PMIC.
  • PCB Size Reduction: Move to 0402 passives, integrate antenna on-board.
  • Mesh Networking: Add sub-GHz mesh stack for multi-hop coverage.
Conclusion
The Firefly Board balances low-power operation, long-range LoRa connectivity, and compact size for off-grid IoT applications. Its modular schematic—with clearly separated power, processing, and RF blocks—enables straightforward customization, while trade-offs in component selection optimize cost and complexity. Future work can focus on extended sensing, energy harvesting, and network topology enhancements to scale into larger deployments.
RF layout guidelines
Solar charging option
External flash for logging
351 days
Sign up to send
U3 is a linear voltage converter designed to protect STM32 and Ra-02 from the vo...
vasyl

vasyl

U3 is a linear voltage converter designed to protect STM32 and Ra-02 from the voltage of a fully charged battery - 4.2V
2y
6
Lithium battery charging 500mA max
vasyl

vasyl

Lithium battery charging 500mA max
2y
2
STM32G030F6P6 is the heart of the board which is controlled by commands from LoR...
vasyl

vasyl

STM32G030F6P6 is the heart of the board which is controlled by commands from LoRa module Ra-02 and turns on/off GPIO(PB7) which is output for lighting control. STM32 also transmits the battery status and can work both from the battery and be completely autonomous.
2y
4
Ra-02 is a board communication module that sends/receives STM32 commands.
vasyl

vasyl

Ra-02 is a board communication module that sends/receives STM32 commands.
2y
5
VBAT
3V3
VBAT
3V3
VIN
VIN
VBAT
3V3
U1
LoRa_RST
C6
Capacitance
0.1uF
U2
LoRa_DI00
SPI1_MOSI
R2
Resistance
470 Ω
R4
Resistance
100KΩ
STM_RESET
C5
Capacitance
10uF
C4
Capacitance
10uF
R5
Resistance
100KΩ
R1
Resistance
2.2KΩ
VBAT_ADC
SPI1_SCK
C7
Capacitance
4.7uF
SPI1_MISO
C8
Capacitance
4.7uF
SPI1_NSS
LED_OUT
C3
Capacitance
4.7uF
LED1
C1
Capacitance
4.7uF
IC1
C2
Capacitance
4.7uF
U3
  • Ground
    Ground
    A common return path for electric current. Commonly known as ground.
    jharwinbarrozo
    20.5M
  • Net Portal
    Net Portal
    Wirelessly connects nets on schematic. Used to organize schematics and separate functional blocks. To wirelessly connect net portals, give them same designator. #portal
    jharwinbarrozo
    43.0M
  • Power Net Portal
    Power Net Portal
    Wirelessly connects power nets on schematic. Identical to the net portal, but with a power symbol. Used to organize schematics and separate functional blocks. To wirelessly connect power net portals, give them the same designator. #portal #power
    jharwinbarrozo
    11.4M
  • Generic Resistor
    Generic Resistor
    A generic fixed resistor ideal for rapid circuit topology development. Its footprint automatically adapts based on the selected package case code—supporting 0402, 0603, 0805, 1203, and many other standard SMD packages, as well as axial horizontal and vertical configurations. Save precious design time by seamlessly add more information to this part (value, footprint, etc.) as it becomes available. Standard resistor values: 1.0 ohm, 10 ohm, 100 ohm, 1.0k ohm, 10k ohm, 100k ohm, 1.0M ohm 1.1 ohm, 11 ohm, 110 ohm, 1.1k ohm, 11k ohm, 110k ohm, 1.1M ohm 1.2 ohm, 12 ohm, 120 ohm, 1.2k ohm, 12k ohm, 120k ohm, 1.2M ohm 1.3 ohm, 13 ohm, 130 ohm, 1.3k ohm, 13k ohm, 130k ohm, 1.3M ohm 1.5 ohm, 15 ohm, 150 ohm, 1.5k ohm, 15k ohm, 150k ohm, 1.5M ohm 1.6 ohm, 16 ohm, 160 ohm, 1.6k ohm, 16k ohm, 160k ohm, 1.6M ohm 1.8 ohm, 18 ohm, 180 ohm, 1.8K ohm, 18k ohm, 180k ohm, 1.8M ohm 2.0 ohm, 20 ohm, 200 ohm, 2.0k ohm, 20k ohm, 200k ohm, 2.0M ohm 2.2 ohm, 22 ohm, 220 ohm, 2.2k ohm, 22k ohm, 220k ohm, 2.2M ohm 2.4 ohm, 24 ohm, 240 ohm, 2.4k ohm, 24k ohm, 240k ohm, 2.4M ohm 2.7 ohm, 27 ohm, 270 ohm, 2.7k ohm, 27k ohm, 270k ohm, 2.7M ohm 3.0 ohm, 30 ohm, 300 ohm, 3.0K ohm, 30K ohm, 300K ohm, 3.0M ohm 3.3 ohm, 33 ohm, 330 ohm, 3.3k ohm, 33k ohm, 330k ohm, 3.3M ohm 3.6 ohm, 36 ohm, 360 ohm, 3.6k ohm, 36k ohm, 360k ohm, 3.6M ohm 3.9 ohm, 39 ohm, 390 ohm, 3.9k ohm, 39k ohm, 390k ohm, 3.9M ohm 4.3 ohm, 43 ohm, 430 ohm, 4.3k ohm, 43K ohm, 430K ohm, 4.3M ohm 4.7 ohm, 47 ohm, 470 ohm, 4.7k ohm, 47k ohm, 470k ohm, 4.7M ohm 5.1 ohm, 51 ohm, 510 ohm, 5.1k ohm, 51k ohm, 510k ohm, 5.1M ohm 5.6 ohm, 56 ohm, 560 ohm, 5.6k ohm, 56k ohm, 560k ohm, 5.6M ohm 6.2 ohm, 62 ohm, 620 ohm, 6.2k ohm, 62K ohm, 620K ohm, 6.2M ohm 6.8 ohm, 68 ohm, 680 ohm, 6.8k ohm, 68k ohm, 680k ohm, 6.8M ohm 7.5 ohm, 75 ohm, 750 ohm, 7.5k ohm, 75k ohm, 750k ohm, 7.5M ohm 8.2 ohm, 82 ohm, 820 ohm, 8.2k ohm, 82k ohm, 820k ohm, 8.2M ohm 9.1 ohm, 91 ohm, 910 ohm, 9.1k ohm, 91k ohm, 910k ohm, 9.1M ohm #generics #CommonPartsLibrary
    jharwinbarrozo
    1.5M
  • Generic Capacitor
    Generic Capacitor
    A generic fixed capacitor ideal for rapid circuit topology development. You can choose between polarized and non-polarized types, its symbol and the footprint will automatically adapt based on your selection. Supported options include standard SMD sizes for ceramic capacitors (e.g., 0402, 0603, 0805), SMD sizes for aluminum electrolytic capacitors, and through-hole footprints for polarized capacitors. Save precious design time by seamlessly add more information to this part (value, footprint, etc.) as it becomes available. Standard capacitor values: 1.0pF, 10pF, 100pF, 1000pF, 0.01uF, 0.1uF, 1.0uF, 10uF, 100uF, 1000uF, 10000uF 1.1pF, 11pF, 110pF, 1100pF 1.2pF, 12pF, 120pF, 1200pF 1.3pF, 13pF, 130pF, 1300pF 1.5pF, 15pF, 150pF, 1500pF, 0.015uF, 0.15uF, 1.5uF, 15uF, 150uF, 1500uF 1.6pF, 16pF, 160pF, 1600pF 1.8pF, 18pF, 180pF, 1800pF 2.0pF, 20pF, 200pF, 2000pF 2.2pF, 22pF, 220pF, 2200pF, 0.022uF, 0.22uF, 2.2uF, 22uF, 220uF, 2200uF 2.4pF, 24pF, 240pF, 2400pF 2.7pF, 27pF, 270pF, 2700pF 3.0pF, 30pF, 300pF, 3000pF 3.3pF, 33pF, 330pF, 3300pF, 0.033uF, 0.33uF, 3.3uF, 33uF, 330uF, 3300uF 3.6pF, 36pF, 360pF, 3600pF 3.9pF, 39pF, 390pF, 3900pF 4.3pF, 43pF, 430pF, 4300pF 4.7pF, 47pF, 470pF, 4700pF, 0.047uF, 0.47uF, 4.7uF, 47uF, 470uF, 4700uF 5.1pF, 51pF, 510pF, 5100pF 5.6pF, 56pF, 560pF, 5600pF 6.2pF, 62pF, 620pF, 6200pF 6.8pF, 68pF, 680pF, 6800pF, 0.068uF, 0.68uF, 6.8uF, 68uF, 680uF, 6800uF 7.5pF, 75pF, 750pF, 7500pF 8.2pF, 82pF, 820pF, 8200pF 9.1pF, 91pF, 910pF, 9100pF #generics #CommonPartsLibrary
    jharwinbarrozo
    1.5M
  • Generic Inductor
    Generic Inductor
    A generic fixed inductor suitable for rapid circuit topology development. The footprint automatically adapts based on the selected package, supporting standard SMD sizes (e.g., 0402, 0603, 0805) as well as well-known inductor packages such as SDR1806, PA4320, SRN6028, and SRR1260. Standard inductor values: 1.0 nH, 10 nH, 100 nH, 1.0 µH, 10 µH, 100 µH, 1.0 mH 1.2 nH, 12 nH, 120 nH, 1.2 µH, 12 µH, 120 µH, 1.2 mH 1.5 nH, 15 nH, 150 nH, 1.5 µH, 15 µH, 150 µH, 1.5 mH 1.8 nH, 18 nH, 180 nH, 1.8 µH, 18 µH, 180 µH, 1.8 mH 2.2 nH, 22 nH, 220 nH, 2.2 µH, 22 µH, 220 µH, 2.2 mH 2.7 nH, 27 nH, 270 nH, 2.7 µH, 27 µH, 270 µH, 2.7 mH 3.3 nH, 33 nH, 330 nH, 3.3 µH, 33 µH, 330 µH, 3.3 mH 3.9 nH, 39 nH, 390 nH, 3.9 µH, 39 µH, 390 µH, 3.9 mH 4.7 nH, 47 nH, 470 nH, 4.7 µH, 47 µH, 470 µH, 4.7 mH 5.6 nH, 56 nH, 560 nH, 5.6 µH, 56 µH, 560 µH, 5.6 mH 6.8 nH, 68 nH, 680 nH, 6.8 µH, 68 µH, 680 µH, 6.8 mH 8.2 nH, 82 nH, 820 nH, 8.2 µH, 82 µH, 820 µH, 8.2 mH #generics #CommonPartsLibrary
    jharwinbarrozo
    15.8k
  • Terminal
    Terminal
    An electrical connector acting as reusable interface to a conductor and creating a point where external circuits can be connected.
    natarius
  • RMCF0805JT47K0
    RMCF0805JT47K0
    47 kOhms ±5% 0.125W, 1/8W Chip Resistor 0805 (2012 Metric) Automotive AEC-Q200 Thick Film #forLedBlink
    jharwinbarrozo
    1.2M
  • 875105359001
    875105359001
    10uF Capacitor Aluminum Polymer 20% 16V SMD 5x5.3mm #forLedBlink #commonpartslibrary #capacitor #aluminumpolymer #radialcan
    jharwinbarrozo
    1.2M
  • CTL1206FYW1T
    CTL1206FYW1T
    Yellow 595nm LED Indication - Discrete 1.7V 1206 (3216 Metric) #forLedBlink
    jharwinbarrozo
    1.1M

Firefly Board

Firefly Board is part of a smart network designed for wireless control of light, water and other parts of the house in locations where GSM communication and WiFi are not available. #LoRa #smart #IoT #power #led #arm #stm32

Properties

creativecommons.org/licenses/by/4.0/

Pricing & Availability

Distributor

Qty 1

Digi-Key

$7.24–$8.62

LCSC

$1.53

Mouser

$2.57

Controls