SDG #141 690 LED ESP32 WiFi Mini Megaclock - An NTP Wharton Electronics Style Clock

This episode follows the smaller sibling of the NTP Megaclock project: a 690 LED, ESP32 driven display styled after the classic Wharton Electronics studio clocks used in broadcast and industrial timing applications. Rather than buying a finished module, the whole thing is built up from a custom PCB, with the LED array, driver circuitry and the ESP32 development board mounted on a single assembly.

The interesting engineering problem in a clock like this is not timekeeping accuracy, since the ESP32 pulls time over WiFi from an NTP server and effectively never drifts. It is the display: 690 individual LEDs arranged as seven segment digits plus a ring of minute and second markers means a lot of multiplexing, a lot of current management, and a PCB layout where routing density matters more than component count. The build shows why hand assembly of that many parts is impractical and why solder paste, hot air and stencil style workflows, or outsourced SMT assembly, are the sensible route for anything above a few hundred LEDs.

For anyone thinking about replicating it, the takeaways are practical: plan brightness and multiplex duty cycle before committing to a driver scheme, keep the ESP32 on a socketed module so firmware and hardware can be debugged independently, and expect the mechanical side, spacing, diffusion and front panel finish, to influence how good the clock actually looks once lit. The mini version keeps the visual character of the full size Megaclock while being far more realistic to build and to fit on a desk or wall.