VDM3 Is a CRT Vector-Drawn Space Game Built From Scratch

Almost all video graphics today are drawn line by line, so each row of pixels is rendered one after the other to complete the images that make up each frame of the video. That drawing process happens so quickly that it can’t be seen by the human eye, though artifacts like screen tearing sometimes become apparent. That isn’t, however, the only way to draw graphics. With cathode-ray tube (CRT) displays in particular, graphics can be drawn as vectors. One of the most well-known examples of vector graphics was on the Vectrex video game console. Mark Atherton created a similar machine from scratch, called the VDM3, along with a space game to play on it.

Cathode-ray tubes, like you’d find inside old TVs and monitors, produce an image by directing an electron beam onto a screen coated in a material, such as phosphor, that emits light for a brief amount of time when excited by the electrons. Electromagnets are used to deflect the electron beam in the X and Y axes in order to target specific coordinates on the screen. If the CRT is used in a TV, that beam is directed line by line and pulsed to render each frame. But vector graphics can be drawn by simply directing the electron beam along paths to draw lines. That is how an analog oscilloscope works, with voltage and time corresponding to the X and Y axes. In this case, as with the Vectrex console, the electron beam is directed to draw lines that make up the video game graphics.

It takes a high voltage to drive a CRT, so you shouldn’t attempt something like this unless you know what you’re doing. The CRT used for this project was a small D7-16G driven by a custom switching power supply that produces up to 240VDC on the primary side and 600V on the secondary. The deflection is controlled by a Microchip ATmega328P microcontroller through AD7302 DACs (Digital-to-Analog Converters). This is capable of drawing 10,000 vector pairs per second, which works out to 200 simultaneous vectors at a 50Hz refresh rate. Atherton programmed a game, which is similar to the classic Asteroids, to run on the hardware. All of the electronic components are housed within an enclosure made of laser-cut MDF. The only controls needed are a joystick and a few buttons, which three knobs used to adjust the CRT settings. Yes, this is a huge amount of work for such a simple game, but it’s awesome to see long-forgotten CRT vector graphics being used today.