A unique digital clock project built by reverse-engineering a commercial VAF (Voltage, Amperage, Frequency) meter. This project repurposes the meter's enclosure and 7-segment display, driving them with an ESP32 and an RTC module for precise timekeeping.
This project was born from curiosity. Starting with a standard VAF meter, I used a multimeter to reverse-engineer the PCB traces and understand the display driver logic. The original mainboard was replaced (or bypassed) with a custom solution powered by an ESP32.
The result is a retro-industrial style clock that retains the rugged look of the original panel meter while running modern firmware.
The VAF meter's display is a classic example of multiplexing to control a large number of LEDs with limited pins.
- Segment Control: All segment signal pins (A-G, DP) are connected in parallel across the digits.
- Digit Selection: A 74LS145 (BCD-to-Decimal Decoder/Driver) is used to activate one digit (or group of segments) at a time.
- Persistence of Vision: The ESP32 switches between digits rapidly. This happens so fast that the human eye perceives all utilized segments as being lit simultaneously.
By tracing the connections with a multimeter in continuity mode, I mapped the pinout of the display board to the ESP32, allowing full control over the digits.
- Controller: ESP32 Development Board
- Timekeeping: RTC Module (DS3231 or similar)
- Driver: 74LS145 (BCD-to-Decimal Decoder)
- Enclosure/Display: Repurposed VAF Meter Case & 7-Segment Display
The schematic below illustrates how the ESP32 interfaces with the 74LS145 and the display segments.
General Pin Mapping Strategy:
- Segments: Connected directly to ESP32 GPIOs (via current limiting resistors).
- Digit Select: 4 GPIOs from ESP32 connected to the ABCD inputs of the 74LS145.
(Check the code for the exact GPIO pin definitions used in this build.)
| Internal Wiring | Side View |
|---|---|
 |
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- Arduino IDE
- ESP32 Board Manager installed in Arduino IDE.
- RTC Library (e.g.,
RTClibby Adafruit) installed via Library Manager.
- Clone or download this repository.
- Open the
.inofile in Arduino IDE. - Select your ESP32 board model under Tools > Board.
- Verify the pin definitions in the code match your specific wiring.
- Upload the code to your ESP32.
Feel free to fork this repository and submit pull requests. If you have a different model of VAF meter, pinouts may vary—contributions documenting other models are welcome!
This project is open-source. Please check the LICENSE file for details.