A feature-rich DIY circuit for charging 3.7V Li-Ion batteries and visually monitoring their charge level with a 10-LED bar graph.
- Charging: Based on the BQ24075 standalone charger IC.
- Monitoring: Utilizes the LM3914 for a 10-segment LED voltage indicator.
- Power Input: USB-C connector for 5V input.
- Safety: Includes provisions for battery temperature monitoring (NTC).
- Professional Design: Double-sided PCB designed for easy assembly.
- IC1: BQ24075 - Battery Charger
- IC2: LM3914 - LED Driver
- Connectors: USB-C, 2mm JST for battery
- Indication: 10x LEDs (Color code: Red for low, Green for high)
- The schematic and PCB were designed in Altium Develop.
- Find the manufacturing-ready Gerber files in the
Fab Files/Gerber/directory.
- Stencil & Paste: Use the provided Gerbers to order a PCB and stencil. Apply solder paste using the stencil.
- Place Components: Refer to the schematic and component placement diagram.
- Reflow: Use a hot plate or reflow oven for the bottom side, and a hot air gun for the top side.
- Critical Note: The LM3914 requires a scaled-down voltage for the SIG pin. The correct voltage dividers are implemented in this design. (See Troubleshooting for the common mistake).
- Access Designe files online: Click Here to check
| Problem | Symptom | Solution |
|---|---|---|
| Incorrect LED Indication | All LEDs light up regardless of battery voltage. | This is caused by applying the full battery voltage directly to the LM3914's SIG pin. The input must be scaled down via a voltage divider to match the 1.25V reference. This design has the correct resistors. |
| Battery Not Charging | STAT LED does not indicate charging. | Check the input power and the BAT/TS pin connections. Ensure the battery is not deeply discharged. |
A full making-of video, covering the design, assembly, and troubleshooting in detail, is available on my YouTube channel: Click here to watch
This project is released under the MIT License. Feel free to use it for personal or commercial projects.
- Thanks to JLCPCB for manufacturing the PCBs.
- Datasheets provided by Texas Instruments (BQ24075) and Texas Instruments (LM3914).