Wristwatch

Wristwatch Devlog 1
I’m making a wristwatch that can be charged with a USB-C cable. I wanted to challenge myself and make it a bit different from the normal digital wristwatches that’s why I decided to add a built-in MP3 player. I also wanted to add an MP3 player, as I don’t really like carrying my phone everywhere as I listen to music.  Other than the MP3 player the watch will have an Oled screen and three buttons, which I can use to control the screen. 

Before starting the main schema for the connection between the electronic parts like the oled screen and the microcontroller, I designed a circuit to charge two pouch Li-ion 3.7V batteries. For the circuit I used a MCP73831 and a BMS card to safely charge the batteries and I added a USB-C type c breakout so I can charge the batteries safely. I’m using two batteries because I decided to add an MP3 player and the mp3 port uses 3.7V to 5V. So I decided to divide 7.4V with two adjustable regulators (LM2596).

To get 3.7V and 5V from the adjustable regulators I used this equation:
Output Volt= Vout=1.23(1+R1/R2)
R1 is the resistance on the VCC side and R2 is the resistance on the ground side.

For the main circuit I first researched the components to decide which specific models I wanted to use. I decided to use the ESP32 wroom 32 d as my microcontroller, GC9A01 round oled screen, PJ-392 3.5mm as my aux cable port and a small mp3 port. Then I first sketched the schematic in Excalidraw, sorted through my mistakes, and did a double check to make sure I’m not connecting anything wrongly before I made the schematics in KiCad.  

For now the full material list is this (with explanation):
1-For the charge circuit:
Lİ-İON POUCH BATTERY x2
Type C breakout board
A lithium-ion charging IC (MCP73831 is the one I chose)
A BMS card (If you don’t want to have the MP3 you can use one Li-ion battery and no BMS card will be neded)
2 4.7-microfarad polarized fixed capacitors
1 4.7-microfarad nonpolar fixed capacitor
1k, 22k and 5k resistancesyellow and red leds

2-For the main circuit:
2 LM2596 adjustable regulators (if you decide to make the mp3)
GC9A01 oled screen (Adafruit’s OLED screens are great too)
ESP 32 Wroom 32d (you can use another microcontroller but I want to somehow use wifi later in the project.) 
MP3 module
Aux cable port
2 small speakers
A 1.6k and 1k resistor to get 3.3v from the adjustable regulator
A 1k and 3k resistor to get 5V from the adjustable regulator
A 1k resistor to go between the RST pin and VCC pin of the OLED screen

I haven’t yet decided on what else there could be in the watch, and I’m open to suggestions, and this is my first solo hardware project, so if you have any suggestions or spot a mistake, feel free to correct me. My next step will be designing a PCB for this version.