Jjy sim r3

📡 JJY-SIM R4 (with R3 design references)

Build your own JJY time-signal simulator with an ESP32-C3 or ESP8684!
This compact simulator reproduces the 40 kHz / 60 kHz JJY radio time signal using PWM output,
based on accurate time obtained from NTP.
R2, R3 and R4 share an ESP-IDF firmware codebase.

R4 is the latest model. The older R3 design files are retained for reference.

The firmware version is 1.2.0.

👉 README 日本語版はこちら

R4 / R3 / R2 layout

R3 and R4 use PCB antennas. R4 stacks a main PCB and three antenna PCBs inside the case. R3 integrates the main circuitry and antenna on one PCB, with the antenna extending outside the case.

R2 has an exterior similar to R3, but uses an ESP32-C3 and solder jumpers for resonance selection. It can use the C3 build of the shared firmware. R2 hardware design files are not included in this repository.

The shared R2/R3/R4 firmware sources are in firmware/idf/jjy-sim. R4 is identified by the eFuse field USER_DATA_JJYSIM_HW_GENERATION set to 4. An unconfigured ESP32-C3 runs as R2. A self-built R4 requires this identification field to be programmed. eFuse writes are irreversible; verify the board and main/esp_efuse_custom_table.csv before programming.

See the USB flashing instructions (Japanese).

Board designs are in hardware/KiCad/r3, r4, r4.1 and r4_ant, with shared libraries in hardware/KiCad/lib. Each board has its own PLOT directory. Case models are in hardware/case_3d/r3 and r4.

hardware/KiCad/r4.1 contains an alternative component layout for the R4 PCB. The order of the L/C/R components in the resonant circuit has also been changed to accommodate the new layout.

🪛 Features

• Generates JJY 40 kHz / 60 kHz signals from time obtained via NTP
• Equipped with a PCB antenna (inside the case on R4)
• Shows the time and operating status on an OLED display
• Configures Wi-Fi and operating settings through a web browser
• Supports Hourly Mode, Night Mode and a screen saver
• Distributes time to devices on the LAN as an NTP server
• Supports firmware updates over Wi-Fi via OTA updates

R4 exterior

For reference: the older R3 model below

🛠 Build and Flash (ESP-IDF / CLI)

Use ESP-IDF v5.5.4 and run these commands from firmware/idf/jjy-sim. Arduino builds are not supported.

R3 (ESP8684 / ESP32-C2):

idf.py -B build-c2 -D IDF_TARGET=esp32c2 -D SDKCONFIG=sdkconfig.c2 build
idf.py -B build-c2 -D IDF_TARGET=esp32c2 -D SDKCONFIG=sdkconfig.c2 -p COMx flash monitor

R4 (ESP32-C3):

idf.py -B build -D IDF_TARGET=esp32c3 -D SDKCONFIG=sdkconfig.c3 build
idf.py -B build -D IDF_TARGET=esp32c3 -D SDKCONFIG=sdkconfig.c3 -p COMx flash monitor

Replace COMx with your serial port. partitions.csv defines the OTA partition layout. Migration from the old layout requires USB flashing including the partition table, not just the application image.

Program the R4 identification eFuse

The ESP32-C3 on a self-built R4 needs the identification value 4. Do not run this procedure on R3. eFuse programming is irreversible.

In an ESP-IDF environment, change to firmware/idf/jjy-sim and replace COMx with the port of the target R4. These commands use a USB connection.

First, check the current value:

espefuse --chip esp32c3 -p COMx --before usb_reset --extend-efuse-table main/esp_efuse_custom_table.csv summary

Confirm that USER_DATA_JJYSIM_HW_GENERATION is 0 (unprogrammed) before writing 4 with the command below. If it is already 4, no write is needed. For any other value, do not attempt to overwrite it using this procedure.

espefuse --chip esp32c3 -p COMx --before usb_reset --extend-efuse-table main/esp_efuse_custom_table.csv burn_efuse USER_DATA_JJYSIM_HW_GENERATION 4

Review the target and changes shown by the tool, then follow its confirmation prompt. After programming, run the summary command again and confirm that the value is 4. Restart the board so that the firmware identifies it as R4.

🛠 Build and Flash (VSCode / GUI)

You can also develop this project using VSCode + the ESP-IDF Extension.

■ Recommended Extension

• ESP-IDF Extension (Espressif)

By installing the extension in VSCode, you can perform the following from the GUI:

• Build
• Flash
• Serial monitor

■ Setup

Set up your environment according to the ESP-IDF Extension instructions.

Once the extension is installed, you can run actions such as:

• Build
• Flash
• Monitor

with a single click.

■ Workspace

When opening the project in VSCode, open JJY-SIM.code-workspace in the source-code folder then select your local ESP-IDF 5.5.4 installation and either C3 (R2 / R4) or C2 (R3) configuration.

⚙️ Usage

Refer to the model-specific manuals on the JJY-SIM support page for settings, screens and controls. R4 switches its resonance circuit automatically with the BAND setting. On R3, also set the on-board switch to match the selected BAND.

🔌 Pin Assignment (Main Signals)

🧾 File Structure

💻 Firmware

• The firmware source code is located in the firmware/idf folder.
• This firmware uses a rebuilt library, ported as an IDF component, based on the Arduino OLED driver library used in R2.
  This component is publicly available on GitHub.
  👉 SSD1306 OLED display driver
• storage_key.h contains placeholder values and can be used as-is.
  For better security, you may want to replace them with your own values before building.

🧰 Hardware

• The hardware design files are located in the hardware folder.

• The schematic and PCB design data are in hardware/KiCad.

  • Saved with KiCad 10 (R4 design files require KiCad 10 or later)
  • Gerber data is included in hardware/KiCad/<revision>/PLOT, so the board can be fabricated as-is

• The 3D case data is in hardware/case_3d.

🔧 DIY Assembly

R4 antenna

Building an R4 requires stacking three antenna PCBs. The antenna stack and main PCB fit inside the case.

PCB thickness: 1.6 mm for the main PCB and 0.8 mm for each antenna PCB.

OLED supports (R3 / R4)

Both R3 and R4 PCBs include tab-shaped sections for the OLED supports. Break these sections off during assembly and use them as supports for the OLED.

Case screws

Use hex M2 × 5 mm self-tapping screws to fasten the case.

📸 Appearance / Assembly Examples

The photos below show the R4 board and case.
The design uses a black PCB and a black case so that only the display appears to float visually.

R3 (for reference)

The photos below show the R3 board and case.

⚠️ Caution

The R4 antenna section becomes slightly warm during operation.

This device may radiate farther than expected.
Please make sure to comply with applicable radio regulations when experimenting with it.

🔗 Support / Documentation

For the latest information, setup guide, and detailed usage notes, please see the support page.
👉 JJY-SIM Support Page

Note: The support page is currently available in Japanese only.

📝 Attribution

JJY-SIM is released under the MIT License.
You are free to use, modify, and build upon this project.

When selling, distributing, or publicly releasing something based on JJY-SIM, please include attribution to Shachi-lab / JJY-SIM somewhere visible, such as the product page, documentation, README, package, or other accompanying materials.

Example:

• Designed by Shachi-lab
• Based on JJY-SIM by Shachi-lab
• Inspired by JJY-SIM by Shachi-lab