Currently I’m working on hacking a VFD display from a late 80s calculator (Monroe 3190). It has 6x standard UCN5812A Drivers with the 5V to 50V boost circuit all compactly mounted on the back of the display which is 2 rows by 40 digits with each digit being a 5x7 matrix. A very nice vacuum tube display that I would like to use on some other hobbyist projects.
There are 4 data inputs to the board, serial, blanking, strobe and the clock (around 3Mhz).
I’m looking for a device that will save the four data inputs as the calculator boots up (to start), so then I can analyze the data and try to control the display, replacing the calculator motherboard with a modern SBC.
I was looking at getting a digital O’scope, but I’m starting to think one of the Saleae devices could be a better fit. I’m assuming the protocol used by the Monroe calculator is not standard so I would need to ‘figure it out on my own’.
Does it sound like I’m on the right path? Which Saleae product would you recommend for this sort of project?
Yes, our products are a great fit for this kind of work. I was even recently debugging a parallel character LCD driver interface just a few weeks ago as a side project.
These old interfaces are slow and easy to record. The main question is just how many signals you need to record. You can likely get away with 8 signals, if it’s using one of the 4 bit standard modes (which were designed to be directly compatible with the Intel 4004 bus). These interfaces tend to have a LOT of signals, but generally you don’t need to record all the signals to completely capture the protocol.
It sounds like you have already identified 8 signals of interest. All of our products can record this number of signals. I would recommend Logic 8.
We also have discounts for students, hobbyists, contractors, and startups. You can learn more and find out if you qualify here: Saleae Discounts
For decoding in our software, there are two main options:
If you’re very lucky, this might use the HD44780 protocol, in which case we have a built in decoder.
You can use our “simple parallel” decoder, which allows you to select a clock channel and one or more data channels, and it will compute the parallel word for each clock edge.
Good luck with the project, and we would love to see photos when you get it working!