Project Firefly Board Overview
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Project Overview: Firefly Board
1. Core Functional Blocks
3. Design & Implementation
5. Performance & Challenges
6. Real-World Applications
7. Improvements & Future Enhancements
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.
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
2. Component Summary
| Role | Designator | Part & Link |
|---|---|---|
| Microcontroller | U1 | U1 |
| LoRa Radio Module | U2 | U2 |
| Battery Charger IC | IC1 | IC1 |
| 3.3 V Regulator | U3 | U3 |
| USB-C Power Connector | J4 | J4 |
| Battery Connector | J1 | J1 |
| Programming Header | J3 | J3 |
| GPIO Connector | J2 | J2 |
| Status LED | LED1 | LED1 |
| Reset Pull-up | R3 | R3 – 100 kΩ |
| LED Current-limit | R2 | R2 – 470 Ω |
| Battery-ADC Divider | R4, R5 | R4, R5 – 100 kΩ each |
| Decoupling Capacitors | C1, C2, C3, C4, C5, C6, C7, C8 | C1, … C8 – 0.1–10 µF (0603) |
3. Design & Implementation
-
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.
-
Battery Monitoring
- Divider [R4]/[R5] scales VBAT to ADC range.
- MCU measures VBAT via VBAT_ADC net for charge management and low-battery alerts.
-
Processing & Communication
-
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
| Decision | Trade-Off / Benefit |
|---|---|
| STM32G0 MCU | Low-power, cost-effective vs. limited Flash (32 kB) |
| Off-the-shelf LoRa module | Simplifies RF design vs. slightly larger footprint & cost |
| SOT-23 Li-ion charger | Compact vs. limited charge current (~100 mA) |
| 0603 passives | Small footprint vs. more challenging hand-soldering for prototyping |
| USB-C power only | Modern 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.
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
354 days
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