Miniature power solar booster

I. Project Introduction
A 2x2 5V solar panel system was used as the power source (two panels in series, then connected in parallel with two more panels in series)
. The first panel outputs 5V, 9V, and 12V.
Under midday sunlight, it outputs approximately 12V. At 5V output, the short-circuit current is approximately 300mA.
Input voltage:
![afac2293495f541940566a7932d94f8.jpg] By changing the wiring caps, it can output approximately 5V, 9V, and 12V .
5V output:
![f607c46dcf43e569dd6888d63b5485c.jpg] 9V output: !
![51b8a3b40206a5d715157ed6353f238.jpg] Second board: After connecting to the 5V output voltage of the first board (or external power supply), it is stepped down to 3.3V through LDO or charged to

3.3V through TP4056
![db3db3cf96695727c24bde5c672dbab.jpg]
Lithium battery charging (charging current set to 120mA)
Charging voltage is around 4V
![3ed7d9d4f850269fc6734f570988b91.jpg] Charging indicator light
![e1e2d60efa1d6f8ab4c02dcfe066a45.jpg]
II. Precautions
1. Both boards are only used for voltages below 300mA. The first board's output voltage can be changed by adjusting the resistance ratio of R7, R6, R4, and R3 (refer to the chip datasheet for details). The second board's charging current can be changed by altering the resistance of R8 (the datasheet states that noticeable heat will occur when the current exceeds 0.5A).
2. The second board's PCB has a grounding DRC error; the 3.3V and charging modules are not grounded correctly. Ignore the DRC grounding error.
3. The solar panel should be used under sunlight; otherwise, the current will be too low, causing a voltage drop after connecting a load. The input voltage should be above 4V, with a certain voltage difference between it and the output voltage.
2. The board makes a sound when connected to a load, which may be due to improper selection of inductors and capacitors.