Overview & Decision Tree

A scope clock tells the time by steering a single electron beam across the face of a cathode-ray tube, drawing the hands, digits, or characters as a vector image — line by line, the way an oscilloscope draws a Lissajous figure — rather than scanning a raster the way a television does. The result is a glowing, faintly humming green (or amber, or blue) display with the analog warmth of a 1950s lab instrument and none of the pixels of a modern screen. It is, for a certain kind of builder, the most satisfying clock there is to make: it combines high-voltage analog electronics, a microcontroller doing real-time waveform synthesis, a genuinely dangerous power supply, and a vacuum tube that you can watch think.

This twelve-volume reference covers the scope clock at depth — the physics of the display, the high-voltage and amplifier electronics that drive it, the firmware that paints the face, how to choose and source a CRT, the two designs the owner of this hub already has on the bench, the buy-it-finished options, the from-scratch open-source path, the enclosure and steampunk treatment, and the safety, calibration, and troubleshooting discipline that ties it all together. It is written for an experienced maker with an electronics bench, an oscilloscope, and a healthy respect for voltages that can stop a heart.

1.1 What a scope clock actually is

Strip away the romance and a scope clock is four subsystems wired together:

1. A cathode-ray tube (CRT) — specifically an electrostatic-deflection CRT, the small round kind used in oscilloscopes and radar indicators, not the magnetic-deflection kind from a television. The beam is steered by voltages on internal deflection plates, which makes it easy to drive from an amplifier instead of a deflection-coil yoke.
2. A high-voltage power supply — the tube needs a few hundred volts to several kilovolts on its anode to accelerate the beam, plus a focus voltage, a grid bias, and a low-voltage heater supply. Generating and taming those rails is the single hardest and most dangerous part of the build (covered in Vol 3).
3. Deflection and video amplifiers — the X and Y plates each need a pair of complementary high-voltage drive signals; the cathode or grid needs a fast “video” signal to blank the beam during retrace so you don’t see the lines connecting one stroke to the next (Vol 4).
4. A timebase and a vector generator — a microcontroller keeps the time and, many thousands of times per second, emits the X, Y, and Z (brightness/blanking) values that trace out the clock face through a pair of digital-to-analog converters (Vol 5).

The vector approach is what gives the scope clock its character. Because the beam goes only where it is told, the “face” can be anything the firmware can describe with line segments and points: analog hands, seven-segment digits, a sine-wave seconds sweep, scrolling text, even a playable game of Zork or a vector Asteroids. A raster display of the same resolution would need far more bandwidth and would look like a tiny television; the vector display looks like an instrument.

1.2 A one-paragraph history

The scope clock descends directly from the test equipment it imitates. Electrostatic CRTs were mass-produced from the 1930s through the 1970s for oscilloscopes, radar PPI displays, and vectorscopes. Hobbyists have been drawing clocks on surplus tubes for decades, but the modern microcontroller scope clock — a small PCB, a cheap CRT, and an AVR or PIC doing the vector math — was popularized in the late 2000s, most influentially by the Dutchtronix AVR Scope Clock (2008, designed by Jan Bart classically known online as “Dutchtronix”), which became the reference design that launched a hundred variants. The British Sgitheach “scope clock” project and Eric Schlaepfer’s (TubeTime) open-source electrostatic CRT driver carried the torch into the open-hardware era, and a healthy cottage industry of kits and finished clocks (Oscilloclock, various AliExpress controller boards) exists today. The history is told in full in Vol 2.

1.3 The six ways to get a scope clock

There is no single “the” scope clock — there is a spectrum of paths from “buy a finished one” to “machine the chassis and roll your own firmware.” This hub recognizes six first-class paths, and the rest of the series is organized so that whichever one you choose, there is a volume that goes deep on it.

#	Path	Effort	Cost	Covered in
1	Buy a finished clock (Oscilloclock-class)	none	$$$$	Vol 9
2	Buy an AliExpress controller board + supply your own CRT	low	$$	Vol 9
3	Build the Dutchtronix AVR Scope Clock from board + parts	medium	$$	Vol 7
4	Build the OSC4.4 from board + parts (the owner’s other unit)	medium	$$	Vol 8
5	Build from the open-source TubeTime crt-driver board set	high	$$	Vol 10
6	Design from scratch — your own PCB, your own firmware	very high	$	Vol 10

Paths 3 and 4 are the sweet spot for most builders and are exactly what the owner of this hub has done: both the Dutchtronix AVR Scope Clock and the OSC4.4 are owned and on the bench (flagged “I have this” in the source folders). Those two get a full build volume each.

1.4 Decision tree — which path is right for this build session

Work top-down; stop at the first “yes.”

• Do you want a clock on the shelf this week with zero electronics risk, and budget is no object? → Path 1, buy a finished Oscilloclock. Go to Vol 9.
• Are you comfortable wiring a CRT and a mains transformer but don’t want to assemble a through-hole board? → Path 2, an AliExpress controller board + a sourced CRT. Vol 9 for the board, Vol 6 to pick the tube, Vol 12 for the safety brief before you energize it.
• Do you want the canonical hobby build, with the deepest community support and the most documented firmware? → Path 3, the Dutchtronix. Vol 7.
• Do you want the build the owner can support directly from in-hand experience, with the most detailed step-by-step (HV → low-voltage → deflection → CRT bring-up) and built-in Wi-Fi/GPS time sync? → Path 4, the OSC4.4. Vol 8.
• Do you want maximum control of the analog electronics — a stiff 1 kV supply, true differential deflection amps, a 6 MHz video amplifier — and you are choosing an unusual or large CRT? → Path 5, the TubeTime open-source crt-driver. Vol 10, with Vol 6 for tube choice.
• Do you want to design your own board and write your own vector firmware? → Path 6. Vol 10 covers the architecture; Vols 3–5 are the engineering reference you will live in.

Whatever the path, Vol 12 (safety) is mandatory reading before the first power-up — every one of these paths involves voltages that can kill.

1.5 What the owner already has

Two designs are owned and serve as the worked examples throughout the series:

• Dutchtronix AVR Scope Clock (owned) — the classic ATmega-based design. The hub holds the full document set (assembly, schematics, operating manual, firmware-update guide, a function-generator mode, and a serial terminal interface) plus firmware hex images (ScopeClock4 V2 2015 and V3 2021) and the V4.3 source. Covered in Vol 7.
• OSC4.4 (owned) — a later through-hole design with a documented 300 V supply, a transistor wave-shaper, and optional Wi-Fi and GPS time-sync modules. The hub holds the full assembly instructions, parts list, CRT pinouts for the DG7-32 and 6Lo1i tubes, and the measured operating voltages. Covered in Vol 8.

FIGURE SLOT 1.2 — Side-by-side photos of the two owned units (Dutchtronix and OSC4.4), ideally powered and displaying a face. Build photos to be taken.

Both are electrostatic-CRT designs in the few-hundred-volt class, which makes them representative of the whole category — the engineering volumes (3, 4, 5) use them as running examples.

1.6 How this series is organized

The series moves from principle to practice to project to polish:

• Principle (Vols 2–6) — how the display works, then each subsystem in turn (HV supply, amplifiers, firmware), then how to choose a tube. Read these to understand any scope clock.
• Projects (Vols 7–10) — the two owned builds, the buy-it options, and the from-scratch open-source path. Read the one that matches your chosen path from § 1.4.
• Polish (Vols 11–12) — the enclosure and steampunk treatment, then the safety/calibration/ troubleshooting reference and the laminate cheatsheet.

1.6.1 Volume-by-volume index

Vol	Title	Read it for
1	Overview & Decision Tree	(this volume) — the map and the path choice
2	How a CRT Vector Display Works	the physics: gun, deflection, phosphor, vector vs raster
3	The High-Voltage Power Supply	generating and taming the anode/focus/bias/heater rails
4	Deflection & Video (Z) Amplifiers	X/Y differential drive and the cathode/grid video amp
5	Timebase & Vector-Drawing Firmware	the MCU, DACs, and how the face is actually drawn
6	CRT Selection & Sourcing	the compatibility list, bases, pinouts, where to buy
7	Build A — Dutchtronix AVR Scope Clock	building and operating the owned Dutchtronix
8	Build B — OSC4.4	the owned OSC4.4, step by step, with bring-up and modules
9	Buy a Kit or Finished Unit	Oscilloclock, AliExpress boards, kits — trade-offs
10	Build From Scratch (open-source)	the TubeTime crt-driver board set and rolling your own
11	Enclosure, Finishing & Steampunk	the chassis, HV clearances, brass, the steampunk look
12	Safety, Calibration, Troubleshooting	HV discipline, focus/centering, fault-finding, cheatsheet

1.7 What this series is — and is not

It is a build-and-understand reference for electrostatic-CRT vector clocks, grounded in two designs the owner has actually built and the open-source designs the community has published.

It is not a substitute for the original designers’ documentation when you build their boards — Vol 7 and Vol 8 point you at the canonical assembly instructions and reproduce the critical data (pinouts, voltages, setup sequences), but you should build with the original documents open alongside. Nor is it a magnetic-deflection (television/monitor) CRT reference — those tubes use deflection yokes and a very different drive architecture, and are out of scope.

1.8 Safety, stated once up front

Every path in this series involves a power supply that produces hundreds of volts to several kilovolts, often derived directly from the AC mains, behind capacitors that stay charged after the clock is unplugged. A CRT is an evacuated glass envelope that can implode if cracked. These are not hobby-electronics voltages; they are the voltages that the safety literature is written about. The full discipline — discharge procedure, one-hand rule, isolation transformer, bleeder resistors, eye protection — is in Vol 12 and the hub-wide _shared/safety.md. Read it before you energize anything. Throughout this series, a ⚠ marks a step where those rules are in force.

1.9 Photo policy

Photographs in this series come from three sources, credited in every caption: the owner’s own build photos and reference collection; license-clean images from Wikimedia Commons / Openverse fetched through the project’s Photo Helper (with the full attribution line reproduced verbatim); and, for non-photographic diagrams, hand-authored SVG. Where a figure is still to be sourced it appears as a FIGURE SLOT placeholder describing what should go there. No images are scraped from arbitrary copyrighted web pages.

1.10 References (Vol 1)

• Dutchtronix AVR Scope Clock — designer documentation set (assembly, schematics, operating, firmware update, function generator, terminal). Held in 02-inputs/A - Dutchtronix AVR Scope Clock/.
• OSC4.4 — assembly instructions, parts list, CRT pinouts and operating voltages. Held in 02-inputs/OSC4_4/.
• E. Schlaepfer (TubeTime), “Electrostatic CRT Driver Design,” tubetime.us/?p=183, and the crt-driver open-hardware repository. Held in 02-inputs/A - Open Source/.
• Sgitheach scope-clock project and open-source code, sgitheach.org.uk/scope2.html.
• NYC Resistor, “Vector Display” introduction, nycresistor.com/2012/09/03/vector-display/.
• “Oscilloscope Clocks” resource compilations. Held in 02-inputs/PDF Resources, Ideas, and Schematics/.