ESP32 radio clock signal repeater

Radio-controlled clocks can automatically receive low-frequency time code signals for precise time synchronization, but they may fail to receive signals in areas with weak signal strength. This project utilizes an ESP32-C3 to synchronize with NTP via Wi-Fi and uses GPIO to simulate radio wave transmission. Testing showed successful time synchronization within a short distance (20cm). A
5-turn coil is drawn on the PCB copper foil for signal transmission .
The design uses a lithium battery for power, with the ESP32 operating at 3.0V. A higher current LDO is recommended; testing with an XC6206-3.0
battery holder showed a 4-pin design, with the middle two pins used for TX and RX
signals. Since the voltage was slightly low, power was drawn directly from the battery, ranging from 3.3V to 4.2V. Higher voltages would require a boost converter, but this would increase power consumption.
The Type-C port serves as both a charging and programming port. Testing showed that it automatically enters download mode on an Arduino and automatically restarts after programming, which is very convenient.
There are many similar programs on GH. I chose a simplified version: GitHub - shuji009/ESP32_jjy_40kHz: ESP32-WROOM-DAを使用したJJYエミュレータ（超简易版）.
The SSID and password need to be set. The
default is JJY40. If JJY60 is changed to 60000,
there is also Shangqiu BPC code. However, I did not have the corresponding equipment and did not test it. GitHub - tarohs/nisejjy: ESP32 fake radio clock station.
After compilation and burning, GPIO emits a wave. It can be received
after soldering the board (the flying wire in the picture has been modified to the circuit and PCB).
This project only uses 1 GPIO port. In order not to waste resources, an e-ink screen driver is included. It can be put into the original price tag box and is intended to display a perpetual calendar, which is updated once a day.
If there is no such need, the relevant components can be left unsoldered.