Schematic for Firefly Board: Firefly Board is part of a smart...

Project Firefly Board Overview

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General (prev)

Project

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

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
- 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]).
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.

RF layout guidelines

Solar charging option

External flash for logging

267 days

Ready.

U3 is a linear voltage converter designed to protect STM32 and Ra-02 from the vo...

vasyl

U3 is a linear voltage converter designed to protect STM32 and Ra-02 from the voltage of a fully charged battery - 4.2V

Lithium battery charging 500mA max

vasyl

Lithium battery charging 500mA max

STM32G030F6P6 is the heart of the board which is controlled by commands from LoR...

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.

Ra-02 is a board communication module that sends/receives STM32 commands.

vasyl

Ra-02 is a board communication module that sends/receives STM32 commands.

VBAT

LoRa_RST

Capacitance

0.1u F

LoRa_DI00

Capacitance

4.7u F

3V3

VBAT

3V3

VIN

LED1

SPI1_MOSI

VIN

Resistance

470 Ω

Resistance

100K Ω

STM_RESET

Capacitance

10u F

Capacitance

4.7u F

VBAT

IC1

Capacitance

10u F

Resistance

100K Ω

3V3

Resistance

2.2K Ω

VBAT_ADC

Capacitance

4.7u F

SPI1_SCK

Capacitance

4.7u F

SPI1_MISO

Capacitance

4.7u F

SPI1_NSS

LED_OUT

Reviews

Electrical Rule Checks

Duplicate Designators

Reports components with identical designators.

No-Connect Violation

Reports no-connect pins that are connected.

Missing Power • 4

	Component
	STM32G030F6P6 U1
	TYPE-C-31-M-12 J4
	AP2112K-3.3TRG1 U3
	MCP73831T-2ACI/OT IC1

Single Pin Nets • 1

	Component
	J4:DN1

Missing Designator

Reports components without a designator.

Design Rule Checks

Overlapping Copper

Reports copper elements that are shorting.

Invalid Layer

Reports nodes that are assigned to a layer that doesn't exist in the layout stackup.

Component Overrides • 20

	Designator	Ruleset
	＊｀REF｀＊	R3
	＊｀REF｀＊	C3
	＊｀REF｀＊	C2
	＊｀REF｀＊	C5
	＊｀REF｀＊	C8
	＊｀REF｀＊	R1
	＊｀REF｀＊	J4
	＊｀REF｀＊	J3
	＊｀REF｀＊	R5
	＊｀REF｀＊	U1
	＊｀REF｀＊	C7
	＊｀REF｀＊	C1
	＊｀REF｀＊	R4
	＊｀REF｀＊	C4
	＊｀REF｀＊	C6
	＊｀REF｀＊	R2
	＊｀REF｀＊	IC1
	＊｀VALUE｀＊	C1 value
	＊｀VALUE｀＊	C3 value
	＊｀VALUE｀＊	C2 value

Airwires

Reports missing routed traces between pads in a net.

Layers with Multiple Fills

Reports layers that have multiple copper fills of different nets. Make sure the Connected Layers rule value of nets with fills is valid.

Floating Copper

Detect any via, trace or copper fill island that is not connected to any net.

Protected Intrusions

Reports intrusions from objects of other nets into polygons or fills that have the Protected layout rule applied.

Missing Footprints

Reports components that need a footprint but don't have one.

Manufacturing

Manufacturer Part Number • 15

	Designator	MPN
	C1	None
	C2	None
	C3	None
	C4	None
	C5	None
	C6	None
	C7	None
	C8	None
	J2	None
	J3	None
	R1	None
	R2	None
	R3	None
	R4	None
	R5	None

Parts Available

Beta

Checks that all components are available from distributors.

System Checks

Auto-Layout

Beta

Reports issues with Auto-Layout if Flux cannot route something or must ignore a configuration.

Passive Components

Resistor Power Rating

Beta

Checks that the power traveling across a given resistor is under its rating with 50% headroom.

Learn more

Pull Up/Pull Down Presence

Beta

Checks that IC pins that require pull up or pull down resistors have them.

Learn more

Capacitor Voltage Rating

Beta

Checks that capacitors have appropriate voltage ratings to prevent overheating and ensure reliable circuit operation.

Ground
A common return path for electric current. Commonly known as ground.
jharwinbarrozo
20.5M
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
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
A generic fixed resistor for rapid developing circuit topology. Save precious design time by seamlessly add more information to this part (value, footprint, etc.) as it becomes available. Standard resistor values: 1.0Ω 10Ω 100Ω 1.0kΩ 10kΩ 100kΩ 1.0MΩ 1.1Ω 11Ω 110Ω 1.1kΩ 11kΩ 110kΩ 1.1MΩ 1.2Ω 12Ω 120Ω 1.2kΩ 12kΩ 120kΩ 1.2MΩ 1.3Ω 13Ω 130Ω 1.3kΩ 13kΩ 130kΩ 1.3MΩ 1.5Ω 15Ω 150Ω 1.5kΩ 15kΩ 150kΩ 1.5MΩ 1.6Ω 16Ω 160Ω 1.6kΩ 16kΩ 160kΩ 1.6MΩ 1.8Ω 18Ω 180Ω 1.8KΩ 18kΩ 180kΩ 1.8MΩ 2.0Ω 20Ω 200Ω 2.0kΩ 20kΩ 200kΩ 2.0MΩ 2.2Ω 22Ω 220Ω 2.2kΩ 22kΩ 220kΩ 2.2MΩ 2.4Ω 24Ω 240Ω 2.4kΩ 24kΩ 240kΩ 2.4MΩ 2.7Ω 27Ω 270Ω 2.7kΩ 27kΩ 270kΩ 2.7MΩ 3.0Ω 30Ω 300Ω 3.0KΩ 30KΩ 300KΩ 3.0MΩ 3.3Ω 33Ω 330Ω 3.3kΩ 33kΩ 330kΩ 3.3MΩ 3.6Ω 36Ω 360Ω 3.6kΩ 36kΩ 360kΩ 3.6MΩ 3.9Ω 39Ω 390Ω 3.9kΩ 39kΩ 390kΩ 3.9MΩ 4.3Ω 43Ω 430Ω 4.3kΩ 43KΩ 430KΩ 4.3MΩ 4.7Ω 47Ω 470Ω 4.7kΩ 47kΩ 470kΩ 4.7MΩ 5.1Ω 51Ω 510Ω 5.1kΩ 51kΩ 510kΩ 5.1MΩ 5.6Ω 56Ω 560Ω 5.6kΩ 56kΩ 560kΩ 5.6MΩ 6.2Ω 62Ω 620Ω 6.2kΩ 62KΩ 620KΩ 6.2MΩ 6.8Ω 68Ω 680Ω 6.8kΩ 68kΩ 680kΩ 6.8MΩ 7.5Ω 75Ω 750Ω 7.5kΩ 75kΩ 750kΩ 7.5MΩ 8.2Ω 82Ω 820Ω 8.2kΩ 82kΩ 820kΩ 8.2MΩ 9.1Ω 91Ω 910Ω 9.1kΩ 91kΩ 910kΩ 9.1MΩ #generics #CommonPartsLibrary
jharwinbarrozo
1.5M
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 10,000uF 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 20pF 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
A generic fixed inductor for rapid developing circuit topology. *You can now change the footprint and 3D model at the top level anytime you want. This is the power of #generics
jharwinbarrozo
15.1k
Terminal
An electrical connector acting as reusable interface to a conductor and creating a point where external circuits can be connected.
natarius
RMCF0805JT47K0
47 kOhms ±5% 0.125W, 1/8W Chip Resistor 0805 (2012 Metric) Automotive AEC-Q200 Thick Film #forLedBlink
jharwinbarrozo
1.2M
875105359001
10uF Capacitor Aluminum Polymer 20% 16V SMD 5x5.3mm #forLedBlink #commonpartslibrary #capacitor #aluminumpolymer #radialcan
jharwinbarrozo
1.2M
CTL1206FYW1T
Yellow 595nm LED Indication - Discrete 1.7V 1206 (3216 Metric) #forLedBlink
jharwinbarrozo
1.1M

Inspect

Firefly Board

Controls

Properties

License

https://creativecommons.org/licenses/by/4.0/

Availability & Pricing

Distributor		Qty 1
	Digi-Key	$7.24–$8.62
	LCSC	$1.53
	Mouser	$2.57

Assets

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