HP2VGA: I’ve Been Making Progress

I haven’t posted in a long time. For one thing, work has been busy. Also I have been making progress here and there in a number of ways, none of which directly merit an article. My solution is to briefly sum up all of my progress here.

Renaming the Project

Up to this point the project as been called “CRT Ocilloscope LCD Mod” or “Oscilloscope Mod” which is a bad name because a) It’s primarily a logic analyser with an Oscilloscope option b) It doesn’t actually describe the project. I have now chosen to call the project HP2VGA.

FPGA Development

The last article showed that I decoded a frame in matlab. This has developed and I now have the FPGA in the loop, converting frames in real time to VGA and driving the display. This is currently handled by the Digilent Nexys 4 DDR board which has a massive Xilinx FPGA on it. This will be replaced by my own board with a smaller, cheaper FPGA.

PCB Development

Due to the requirements of the FPGA, I’ve had to use a 0.8mm BGA package which means I’ve had to move to a four layer board – this will be my first four layer board for a personal project and my first BGA design. Overall I think my design has worked out quite nicely at under 4 square inches.

Screenshot from 2018-07-22 22-49-48.png

Driving VGA Signal

I have settled on the ADV7125 as my VGA driver of choice. It has 24-bit RGB output which is probably overkill but will allow me to do grey-scale to RGB conversion if I get round to it.

Removing the CRT

The HP1662AS has a Cathode Ray Tube display that need removing (I also want to use it in a future project). It was a pain to get to, but at least there was a service manual. After removing almost every component from the body I was able to get to the one torque bolt and three 7mm hex-nuts (which required a me to buy a set of box spanners!).

Mounting New Hardware

The new display actually fits pretty nicely, however the display isn’t quite the right aspect ratio so I am going to have to 3D print some parts to cover this up.


The new display fits nicely


The new display fits nicely

I will also print parts to mount the new PCB in the HP1662AS.

3 thoughts on “HP2VGA: I’ve Been Making Progress

  1. Hi, Your project is very interesting. I hope you keep updating us.

    I have an old hp 54201a, and the screen is becoming pale and fuzzy. Do you think it is possible to convert to lcd?

    1. Hi Riccardo. I’m hoping to have this stuff mostly working by the end of the month if everything goes well. I have had a quick look at the service manual for the 54201a and it looks similar to the 1662a so I definitely think it’s possible (you could reuse my design mostly). If you’re interested in talking more, let me know and we can talk on email or something.

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