// Main loop running at 50kHz DAC update rate Vector points[100]; // List of X,Y,Z for clock face
Cathode-Ray Tube (CRT) clocks merge mid-century display technology with modern digital timekeeping. Unlike standard LED or LCD screens, a CRT clock uses an electron gun to draw time directly onto a phosphor-coated glass screen.
The high voltage connects to a resistor string to safely drop voltages for the internal elements:
This paper presents a complete schematic design for a Cathode Ray Tube (CRT) clock. Unlike raster-scan televisions, this design utilizes (similar to an oscilloscope or Vectrex gaming system) to draw analog clock hands and digital text using a microcontroller, Digital-to-Analog Converters (DACs), and analog deflection amplifiers. The paper discusses the theory of electrostatic deflection, the Z-axis (intensity) control, and the software necessary to convert Unix epoch time into geometric vectors. Crt Clock Schematic
Designing a CRT clock schematic requires balancing complex analog deflection circuits with precise digital timing. Essential Components of a CRT Clock Schematic
Mixes of digital high-frequency signals and analog high voltages create immense noise. Connect all ground paths to one single physical point near the power supply.
module for high accuracy, or sync via Wi-Fi (NTP) if using an ESP32. Signal Generation (X-Y Deflection) // Main loop running at 50kHz DAC update
The raw output from a DAC is usually 0V to 3.3V or 5V. A CRT requires much larger voltage swings to bend the electron beam across the entire screen face. Electrostatic vs. Magnetic Deflection
Cathode-Ray Tube (CRT) clocks represent a fascinating intersection of mid-century display technology and modern digital timekeeping. While commercial production of CRTs has ceased, building a clock using these glowing glass tubes remains a highly popular project for electronics hobbyists.
If an electron beam stays stationary on a single point of a CRT screen for too long, it will permanently burn the phosphor. Implement a "beam blanking" or shutdown circuit in your schematic. If the microcontroller crashes or stops sending DAC updates, a hardware transistor should instantly pull the control grid ( G1cap G sub 1 ) highly negative to shut down the electron gun. Essential Components of a CRT Clock Schematic Mixes
MCU Blanking Pin (0V/5V) ---> [ 1k Resistor ] ---> Base of 2N2222 Transistor Emitter to GND Collector to Optocoupler (H11G1) Optocoupler Output ------------> Pulls Control Grid more negative than Cathode (Shuts off electron beam)
The schematic had a notation she could not at first decipher: "Observe for ghosts." It was a joke, she thought. Engineers have a dry humor. But as days passed, she noticed small oddities. Once, at three in the morning, the brass dial clicked forward though no electrical pulse had been sent. The beam traced a path that did not match any of the vectors on her diagrams—a loop that spelled, to her startled imagination, an initial. She began to leave a pencil nearby and, in the morning, found tiny graphite marks where the beam’s arc had crossed the paper, as if the light itself had insisted on making a note.