Inspiration

The inspiration for this project came from seeing how much modern devices depend on electricity. Many people lose access to charging when they are outdoors, traveling, or in emergency situations. We wanted to build a portable power source that can work on its own and use solar energy to charge small electronics. Our goal was to design a system that is compact, efficient, and easy to use. The system shows real-time information such as battery level, charging status, and device power usage.

Categories

Power - The system gathers energy from a 5V solar panel, which is protected by a resettable fuse and a Schottky diode to prevent backflow. The BQ24075 charger IC manages power flow, safely charging a 3.7V Li‑Po battery while simultaneously powering the system when sunlight is available. Additional components like the AP7333 LDO and TPS61023 boost converter regulate the voltages needed for different parts of the circuit, ensuring that the ESP32 receives a stable 3.3V and that USB devices can receive a boosted 5V output for charging. 

Actuation - The system gathers energy from a 5V solar panel, which is protected by a resettable fuse and a Schottky diode to prevent backflow. The BQ24075 charger IC manages power flow, safely charging a 3.7V Li‑Po battery while simultaneously powering the system when sunlight is available. Additional components like the AP7333 LDO and TPS61023 boost converter regulate the voltages needed for different parts of the circuit, ensuring that the ESP32 receives a stable 3.3V and that USB devices can receive a boosted 5V output for charging.

Computation - The ESP32‑S3 serves as the computational brain of the device. It continuously measures battery voltage, monitors solar input, detects whether a device is plugged in and drawing current, and evaluates overall system status. Using this data, it communicates real‑time information to users via a 0.96-inch OLED display. The microcontroller also manages logic such as disabling charging when the battery is full or interpreting 5V voltage sag as a sign that an external device is charging. 

Code - The ESP32‑S3 serves as the computational brain of the device. It continuously measures battery voltage, monitors solar input, detects whether a device is plugged in and drawing current, and evaluates overall system status. Using this data, it communicates real‑time information to users via a 0.96-inch OLED display. The microcontroller also manages logic such as disabling charging when the battery is full or interpreting 5V voltage sag as a sign that an external device is charging.

Functionality

• The Solar Charging Station uses solar energy and smart power control to act as a portable charger. A 5-volt solar panel generates clean power. This power first passes through a fuse and a Schottky diode to protect the system. 

• The BQ24075 charger IC safely charges a 3.7-volt Li-Po battery. It can power the system and charge the battery at the same time. A thermistor monitors the battery temperature to keep it within safe limits. 

• The power is then regulated for different uses. A 3.3-volt LDO powers the ESP32-S3 microcontroller. A TPS61023 boost converter creates a steady 5-volt output for charging devices like phones. The ESP32 tracks battery level, solar input, and the 5-volt load to detect when a device is charging. All this information is shown on a 0.96-inch OLED screen for the user.

Bills of Materials (BOM)

• Core Electronic

  • ESP32‑S3‑WROOM‑1 Module Main

  • BQ24075 Battery Charger IC 1‑cell Li‑ion 

  • TPS61023 Boost Converter (5V Output) 

  • AP7333‑3.3 LDO Regulator Provides stable 

• Power Components

  • 3.7V 2500mAh Li‑Po Battery 

  • Adafruit 5V 1.2W Solar Panel 

  • Resettable PTC Fuse (0ZRR0135FF1A) 

  • Schottky Diode (SS14) 

  • Inductor 1µH for boost converter

• Connectors

  • USB‑C Power‑Only Receptacle (x2) 

  • JST‑PH 2‑pin Battery Connector

• Display

  • 0.96" OLED (SSD1306, I²C)

• Passive Components

  • Capacitors: 10µF, 4.7µF, 1µF, 0.1µF (various ceramic types) 

  • Resistors: Feedback resistors (1.1MΩ, 150kΩ) Divider resistors (100kΩ, 220kΩ, 56kΩ)

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Schematic and Components

Layout

Challenges and Setbacks

Schematic

• Understanding how the BQ24075 charger IC handled solar input, battery charging, and power‑path control took time. 

• Designing correct resistor dividers for battery sensing and 5V detection required calculation and verification. Integrating multiple regulators (LDO + boost converter) introduced complexity in ensuring stable voltage rails. 

• Ensuring the ESP32‑S3 pins were correctly mapped to all required signals (ADC, I²C, enable pins, etc.) caused several revisions.

Layout

• Routing high‑current paths for the charger and boost converter without noise issues or voltage drop. 

• Maintaining a clean RF keep‑out zone under the ESP32 antenna while still fitting the entire design on the board. 

• Positioning the boost converter components tightly to reduce switching noise, while keeping digital traces isolated. 

• Managing ground planes and vias to avoid interference between analog measurements and switching converters.

Soldering

• Soldering the BQ24075 (QFN) and TPS61023 (tiny SOT package) was difficult because the pads were extremely small. 

• The ESP32‑S3 module required careful placement to avoid solder bridges, especially on the underside pads. Making sure every connection, especially the USB‑C pins and test points, was fully soldered with no hidden cold joints was challenging. 

• Some boards became unresponsive due to small soldering mistakes like shorts, incomplete joints, or lifted pads, which took time to diagnose.

Future Improvements

In the future, this project can be improved by using a more efficient solar panel to increase charging speed and overall energy output. A larger battery or support for multiple batteries could extend usage time, especially in emergencies. Adding USB-C with fast-charging support would make the system more compatible with modern devices. The design could also be made more weather-resistant for reliable outdoor use. Wireless charging and a more advanced display or mobile app could improve user experience. Finally, optimizing power management and adding data logging would help reduce energy loss and track system performance over time.

Conclusion

In conclusion, our solar charging station shows how renewable energy, smart power control, and embedded computing can work together in a practical way. By combining a solar panel, a Li-Po battery, a charger IC, voltage regulators, and an ESP32 microcontroller, we created a portable system that delivers reliable 5V power. The system also monitors battery health, solar input, and device charging status in real time. This project highlights how careful circuit design and programming can turn simple components into a useful, self-sustaining solution that supports clean energy and everyday use.

Thank you For an Amazing Semester!