An old-and-busted (but working!) DesignSpark project I made many years ago as PCB design practice. It's intended to convert a composite video baseband signal to a format that can be displayed on an analog oscilloscope, albeit in grayscale.
Like many existing versions of this project, the main functional component is a LM1881 IC, which provides the CSYNC and VSYNC pulse signals to some analog circuitry in order to form a raster (the X and Y outputs). The Z output is the video input passed through an AD8032 op-amp in an inverting amplifier configuration.
Some pictures of the design:
The project schematic.
The PCB layout.
- Connect the XY outputs to the oscilloscope using a 3.5mm audio jack to stereo RCA cable and RCA to BNC adapters. Red is X and white is Y.
- The Z output requires another adapter I didn't have on hand, but ideally would use another RCA cable and RCA to BNC adapter.
- Put the oscilloscope in XY mode and adjust the X scale, Y scale, and brightness to appropriate levels. 0.2 V/div is a good starting value in 1X mode, and adjust vernier scales for fine tuning once the picture is visible. AC coupling is necessary on both inputs as well.
- Connect any composite video source (I used my SNES with the 240p Test Suite) to the video input.
- Set the DC power supply's output to 9V, and connect it to the power inputs as shown below (red is +9V, black is ground).
The PCB fully connected.
Video test output (SMPTE color bars, albeit in grayscale).
Another test output (monoscope pattern shows distinct distortion across the field).
Bonus:
Some DOOM footage from my SNES.
Since I have moved on to other projects, I will not be updating this design. However, there are critical issues that are worth recording.
- The schematic shows D1 and D2 facing the wrong way.
- At the time, transistor arrays were convenient, but those parts are not kept in stock in a large quantity. A redesign using discrete components would be better.
- Power entry can be more clear. Some input protection would be nice as well, getting the inputs backwards will damage most components.
- Use more appropriate connectors for the outputs.
- There are issues with video output, as seen in the test screenshots.
- Contrast adjust doesn't do very much except on the very low end of the scale. A log scale potentiometer would be a better fit.
- Brightness adjust acts very strange and needs work.
- There's nonlinear distortion in the raster output effecting picture quality. This can probably be fixed by adjusting RC values and/or with better transistor selection.
- Probably more.
Feel free to use this design for any purpose you find useful.