Telechron vintage logo
Master Clocks and
Time Distribution
Mitchell Janoff

Meter Clock with NTP Interface

Meter clock circuit diagram

About the Meter Clock

The meter clock is a unique timekeeping project that repurposes analog panel meters -- the type traditionally used to display voltage, current, or other electrical measurements -- to display the time. Instead of a conventional clock dial with hands, this clock uses meter movements with custom scales to show hours, minutes, and seconds.

Design Concept

The meter clock concept takes advantage of the fact that analog meter movements are inherently accurate analog display devices. A D'Arsonval meter movement converts a DC current into a proportional angular deflection of a pointer. By feeding the meter with a current proportional to the current time value, the pointer indicates the time on a custom-marked scale.

For example:

  • An hour meter is driven with a current that steps through 12 levels, one for each hour position.
  • A minute meter receives a continuously varying current proportional to the minutes past the hour (0-59).
  • A second meter similarly tracks seconds.

The NTP Interface

What makes this meter clock particularly interesting in the context of this collection is its Network Time Protocol (NTP) interface. NTP is the internet protocol used to synchronize computer clocks to Coordinated Universal Time (UTC) with millisecond-level accuracy. By incorporating an NTP client, the meter clock obtains its time directly from internet time servers, which are themselves synchronized to atomic clocks.

This represents the modern evolution of the same concept embodied by the Self Winding Clock Company's Western Union time service: obtaining accurate time from a remote authoritative source and distributing it locally. Where the SWCC system used telegraph lines and telephone modems, the meter clock uses Ethernet and the internet. Where the SWCC system achieved accuracy of a few seconds, NTP achieves accuracy of a few milliseconds.

Circuit Design

The schematic diagram above shows the circuit design for the meter clock. The key components include:

  • Microcontroller: Manages the NTP communication, time calculation, and meter drive signals.
  • Digital-to-analog converters (DACs): Convert the digital time values into analog currents to drive the meter movements.
  • NTP client firmware: Periodically queries internet time servers and adjusts the local time accordingly.
  • Meter movements: Standard analog panel meters with custom-printed scales.

Connection to the Collection

The meter clock bridges the gap between the historical mechanical timekeeping of the master clock collection and the modern digital precision of the GPS and cesium standards in the equipment rack. It demonstrates that the fundamental challenge -- obtaining accurate time from a remote source and displaying it locally -- remains the same regardless of the technology used to accomplish it.