The amplifiers must feature a fast slew rate to prevent the drawn vectors from blurring or lagging. High-Voltage Power Supply (HVPS)
The attic was cleared out, and Mira returned to her device with new understanding. The schematic had been less an instruction manual than an invitation: to assemble a machine, yes, but also to become a keeper. She put aside some of her modern habits; she stopped syncing the time on her phone every hour and let the CRT set the cadence for her evenings. She cataloged the objects people left, wrote down the images the beam sketched, and mailed small notes back to neighbors with a line or two about what had appeared that night.
The MJE340 (NPN) and MJE350 (PNP) complement each other to handle up to 300V transitions without overheating. Crt Clock Schematic
| Section | Critical Parts | Value/Rating | | :--- | :--- | :--- | | | Ferrite core (EE25), IRF740 MOSFET, UF4007 diodes | 1.2kV out, 30kHz | | Focus/Bias | High voltage resistor chain (10MΩ + 5MΩ trimpot) | 1W, 3kV rating | | Deflection | APEX PA94 or discrete (BF869/BF870) | +/- 100V @ 50mA | | DAC | MCP4922 (12-bit, dual) | SPI interface | | MCU | Teensy 4.0 or STM32F103 | 72MHz+ for vector speed | | Power | 6.3V AC transformer (for heater) + 24V DC supply | Galvanic isolation |
: Advanced designs integrate Wi-Fi (ESP32) or GPS modules to automatically synchronize time via the internet or satellites, eliminating the need for manual adjustment. Common Components in CRT Clock Kits The amplifiers must feature a fast slew rate
A 12V or 15V DC input power supply feeds the microcontroller and the op-amps.
The Z-axis controls the brightness of the electron beam. Its primary role is : turning the beam off while it moves between drawing positions, preventing unwanted lines on the screen. The Z-axis circuit is often a high-speed amplifier that takes a logic-level signal from the microcontroller and uses it to drive the CRT's control grid. For the smoothest vector drawings, many builders include this feature. She put aside some of her modern habits;
module for high accuracy, or sync via Wi-Fi (NTP) if using an ESP32. Signal Generation (X-Y Deflection)
-1000V Rail ---> [ 1M Ohm Resistor ] ---> To Cathode ---> [ 500k Potentiometer ] -> To Focus Grid ---> [ 500k Potentiometer ] -> To Control Grid (Brightness) 4. Z-Axis Blanking Circuit
Keep the high-voltage generation entirely separate from the low-voltage logic side. Use optocouplers for the Z-axis blanking signal to protect your microcontroller and programming computer from high-voltage spikes.