Smart Solar Li-Po Charging System (STM8S + STM8duino)

Open-source reference design for a microcontroller-controlled solar charger:

• Solar panel input: 5V / 200mA (about 1W)
• Battery: 1S 3.7V Li-Po, charge limit 4.2V
• Controller: STM8S103F3P6
• Firmware environment: Arduino IDE with STM8duino core
• Programming: ST-LINK V2 over SWIM

This repository includes firmware, circuit design, PCB design files, BOM, and bring-up/testing docs.

Features

• Solar voltage monitoring (ADC)
• Battery voltage monitoring (ADC)
• Optional current monitoring (0.1 ohm shunt + amplifier)
• PWM buck-stage control
• Li-Po safety state machine
• Optional perturb-and-observe MPPT loop

Charging Modes

Battery Voltage	Mode	Behavior
< 3.2V	Precharge	Low current target (~40mA)
3.2V to 4.1V	Bulk/Normal	Higher current target (~160mA)
4.1V to 4.2V	CV	Hold near 4.2V
>= 4.2V and low current	Done	PWM off
>= 4.25V	Fault	PWM off (protection)

Repository Layout

.
|-- arduino_lipo_charger.ino                      # Main firmware sketch
|-- firmware/stm8_solar_mppt_charger/
|   `-- stm8_solar_mppt_charger.ino              # Same firmware (folderized)
|-- hardware/
|   |-- bom/
|   |   |-- bom.csv
|   |   `-- bom.md
|   |-- kicad/
|   |   |-- smart_solar_lipo_charger.kicad_sch
|   |   `-- smart_solar_lipo_charger.kicad_pcb
|   |-- schematic/
|   |   |-- smart_solar_lipo_charger_schematic.md
|   |   |-- smart_solar_lipo_charger_netlist.csv
|   |   `-- smart_solar_lipo_charger_schematic.svg
|   |-- pcb/
|   |   |-- smart_solar_lipo_charger_pcb.md
|   |   |-- component_placement.csv
|   |   `-- smart_solar_lipo_charger_pcb.svg
|   `-- manufacturing/gerbers/
|       `-- README.md
|-- Docs/
|   |-- architecture.md
|   |-- firmware.md
|   |-- hardware.md
|   |-- mppt.md
|   |-- programming_stlink.md
|   |-- calibration.md
|   `-- test_plan.md
|-- LICENSE
`-- LICENSE-HARDWARE.md

Hardware Summary

• Inductor: 22uH
• Input capacitor: 220uF
• Output capacitor: 470uF
• Schottky diode: SS14
• Main switch MOSFET: AO3400 (or equivalent logic-level MOSFET)
• Current shunt: 0.1 ohm
• Voltage sense dividers for solar and battery ADC channels

Detailed notes:

• Schematic: hardware/schematic/smart_solar_lipo_charger_schematic.md
• PCB: hardware/pcb/smart_solar_lipo_charger_pcb.md

Firmware Build/Flash (Arduino IDE 2.x)

1. Install Arduino IDE 2.x.
2. Open File -> Preferences.
3. Add board manager URL: https://raw.githubusercontent.com/tenbaht/sduino/master/package_sduino_stm8_index.json
4. Install STM8 core from Boards Manager.
5. Open arduino_lipo_charger.ino.
6. Select board family containing STM8S103F3P6.
7. Select programmer ST-LINK V2.
8. Use Sketch -> Upload Using Programmer.

ST-LINK wiring:

• SWIM -> SWIM
• GND -> GND
• NRST -> NRST (recommended)
• 3V3/5V -> target VCC as required

Full guide: Docs/programming_stlink.md

Safety Notes

• This is a development reference design, not a certified charger.
• Verify ADC scaling and calibration before connecting real batteries.
• Use a protected Li-Po cell or external protection circuit.
• Validate with a dummy load before field deployment.

License

• Firmware/code: MIT (see LICENSE)
• Hardware documentation and design files: CERN-OHL-S-2.0 (see LICENSE-HARDWARE.md)