Crt Clock Schematic

A CRT clock schematic is more complex than a digital clock, but far more rewarding. The glow of real phosphors tracing the time in vector form is a piece of functional art.

If you’re new to high voltage, build the deflection and Z-axis first and test using an oscilloscope in XY mode. Then add the HV supply. And always – one hand in pocket when probing live circuits.

Have you built a CRT clock? Share your schematic and photos in the comments below.

The following is a technical narrative describing the design and logic of a discrete logic CRT Clock, a device that turns the ephemeral nature of time into a physical dance of electrons. Crt Clock Schematic

At the input side of the schematic, one finds a conventional timekeeping source. This is typically a microcontroller (like an Arduino or PIC) or a dedicated real-time clock (RTC) chip connected to a 32.768 kHz crystal oscillator. This low-voltage digital section generates the raw data: hours, minutes, and seconds.

However, a CRT cannot display numbers natively. Therefore, the schematic includes a character generator—historically a ROM chip like the 2513, but in modern designs, part of the microcontroller’s code. This logic translates the binary time data into vector or raster coordinates. For a vector CRT clock, the microcontroller outputs analog voltage levels (via digital-to-analog converters or resistor ladders) corresponding to the lines that form each digit.

In an age dominated by silent, flat-panel displays and voice-activated smart devices, the warm, glowing flicker of a cathode ray tube (CRT) seems like a relic from a bygone era. Yet, for a niche community of engineers, hobbyists, and retro-computing enthusiasts, the CRT remains a medium of fascination. One of the most compelling projects that bridges the gap between obsolete hardware and functional art is the CRT Clock. Examining the schematic of a CRT clock reveals not just a method of telling time, but a masterclass in analog circuit design, high-voltage safety, and the innovative repurposing of electrostatic deflection. A CRT clock schematic is more complex than

// Lookup table for digit '0'
int zero[5][2] = 0,0, 10,0, 10,20, 0,20, 0,0;

void drawVector(int x, int y, bool draw) 
digitalWrite(Z_AXIS, draw); // Turn beam on/off
delayMicroseconds(2);       // Settling time
analogWrite(X_DAC, x);
analogWrite(Y_DAC, y);
delayMicroseconds(20);      // Deflection speed

Refer to Figure 1 (Conceptual Schematic): The MCU outputs a 0-3.3V signal. The CRT needs approximately ±20V to move the beam edge-to-edge. Have you built a CRT clock

Formula for Deflection: $$ D = \fracL \cdot V_d2 \cdot d \cdot V_a $$ Where ( D ) is deflection (mm), ( L ) is plate length, ( d ) is plate gap, ( V_d ) is deflection voltage, and ( V_a ) is anode voltage.

Before we read the schematic, let’s visualize the signal flow. A typical vector-based CRT clock (e.g., the infamous "Vyzkum" or "Joule" designs) consists of five core subsystems:

Back to the Movies