VGA to X-Y-Z scope converter

This is a fun project I found on Jon’s antique radios web-page. He has managed to convert the VGA output signal from PC to X Y X oscilloscope signal. Converting the VGA RGB signal to a synchronized oscilloscope input signal is pretty easy because VGA has two sync signals separate from RGB signals. Look at pin-out of VGA cable:

Sync signals make things much easier as there is no need for additional sync signal generators – thus circuit becomes pretty simple without any programmable components:

The sync signals are taken from the VGA cable trigger sweep tooth signal (555 timers) generators. These generators generate ram signals for oscilloscope, which enable the creation of a raster pattern. The vertical generator frequency is around 75Hz, and horizontal about 35kHz is used as horizontal sync pulses. Output sync (75Hz) is fed to oscilloscope Y-axis, and 35kHz sync signal is fed to the X-axis of the oscilloscope. The circuit is ready for 800 x 600 at a 75Hz refresh rate. For different configurations, you might need to adjust horizontal and vertical sync 555timers RC circuits.

The RGB signal is converted to a monochrome signal and fed to the Z-axis of the oscilloscope as intensity.

Inside the box:

Be sure that you turn the PC before switching the oscilloscope ON; otherwise, without a PC sync signal, you will get a bright dot on the Oscilloscope screen that can burn the phosphor. When turning off – turn the oscilloscope first before turning off the PC.

Circuit is sensitive to voltage swings. Be sure that you have stabile +5V.

PC desktop image:

The image on oscilloscope:

References: Jon’s antique radios.


  1. This is great project :-). I wouldn’t believe ordinary oscilloscope is capable of displaying fast VGA signal in XY mode.

    btw, you might be interested in some VGA Microcontroller projects at

  2. smirdiigs tev tas suuds sanaacis, es no govs suudiem labaaku vareetu uztaisiit

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