A Converted Nixie Tube Frequency Counter Makes for an Awesome Clock
Scoops found a beautiful vintage frequency counter in a pile of e-waste and used an ESP8266 to transform it into a terrific timepiece.
Most time-keeping devices are really just counters, with intervals between counts as regular as possible. A grandfather clock keeps the count regular through the motion of a swinging pendulum, while an atomic clock keeps extraordinarily regular count intervals by detecting the radio waves emitted by a moving atom like cesium. The frequency of the radio wave emissions, which can be more than nine billion cycles per second, is incredibly precise. With this concept in mind, Scoops came to the conclusion that a frequency counter would make for a perfect clock. He found a vintage Nixie tube General Radio frequency counter from 1972 and was able to convert it into an awesome clock.
A frequency counter is an electronic instrument that has the sole purpose of measuring the number of cycles of an oscillating electrical signal. Modern frequency counters come in the form of tiny IC (Integrated Circuit) chips, but they were quite large analog devices in the days before digital instruments became commonplace. Because precision is important and many signals have a very high frequency, these counters have readouts with several digits. This particular model, a General Radio 1192-B, has six digits, which makes it great for use as a clock that displays the current time in hours, minutes, and seconds. Each digit is displayed in the beautiful orange glow that only a Nixie tube can provide.
As a counter, this device is designed to roll over each digit from 9 to 0. But, of course, we don’t measure time like that. Seconds and minutes need to roll over from 9 to 0 until reaching 60, at which point it rolls back over to 0. Similarly, hours need to roll over at either 12 or 24 counts. This meant that Scoops couldn’t just use a constant frequency, because that would cause the time to go from 12:59:59 to 12:59:60 instead of 01:00:00 as it should. To get around that, he had to increase the frequency at the proper times to quickly roll the digits forward to where they should be. That is handled by an ESP8266 NodeMCU board.
The ESP8266 pulls the current time using NTP (Network Time Protocol). The board’s built-in DAC (Digital-to-Analog Converter) is used to generate an analog signal with the proper frequency, which is increased when the digits need to be rolled forward from 6 to 0 or 12 to 1. The counter has to be reset every 12 or 24 hours (demonstrated here at 12 hours) and a 5V signal is required to perform that reset. A simple 2n3904 transistor and a pair of resistors are used as a level shifter to produce that 5V reset signal when needed. The result is a beautiful retro clock built using an upcycled piece of obsolete equipment.