HP2VGA: Project Write Up

Introduction

This project started about two and half years ago when I took an FPGA class at MIT and the professor happened to give me an HP1662AS logic analyser that MIT were throwing out. Despite the fact that I lived in the UK and this thing is massive and weighs 20kg I took it anyway. I thought it would be a cool project to replace the cathode ray tube with a larger, LCD display. I thought I would get this done before I left the US three months later… Little did I know it was going to take me another two years (although not of continuous work). Now I am nearly done, and just in time to ship it back to the US when I move back for work.

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The HP1662AS on the desk where it was left for me in MIT

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Project: CRT Oscilloscope LCD Mod – Choosing the replacement LCD

I’m replacing the screen on the logic analyser for a few reasons:  The CRT is heavy and bulky – replacing it would make the whole thing lighter, an LCD could be brighter and I can add colour to the monochrome display, and on top of this it’s just an interesting project. The most important thing is that the replacement screen is not worse than the old one!

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Project: CRT Oscilloscope LCD Mod – Simulating signals

After putting this project on the back burner, I am focusing on it once again. Brian HG on the EEVblog forums suggested that a simple line doubler would make the signal compatible with most modern VGA displays. What that means is that each line in the frame needs to be repeated twice, at double the speed.

Currently we get a new line every 40 microseconds, but this is too slow for most displays to be happy about. Therefore, if we record each line and output it twice at 20 microseconds each most VGA displays will be ok with it.

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Project: CRT Oscilloscope LCD Mod – Motivation

Last semester I was given a decommissioned HP 1662As Logic Analyzer/Oscilloscope from MIT. This is quite a nice piece of test equipment, if not a little bit old (made in the early ’90s). 68 channels of 250MHz logic analyser and a 2 channel 250MHz oscilloscope are nice specs but a grey-scale CRT display and floppy drive show it’s age.

The trouble is that it is huge. At 442x218x330mm it is far to big to fly back to the UK with me. Considering the CRT takes up about 50% of the space inside I thought it would be an interesting project to try and replace the CRT display with an LCD monitor and shrink the whole package.

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Pretty big

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