CDU export with 4" display and Raspberry PI. How to? - ED Forums
 


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Old 07-09-2019, 05:36 PM   #1
760mm
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Default CDU export with 4" display and Raspberry PI. How to?

Is there a way to export a CDU to a 4" display via a Raspberry PI? I need a detailed guide or practical advice.
Or the only way to export a CDU to the screen is to use an HDMI display connected to PC using Helios or Icarus. I'm afraid that the use of additional display (except for the two MFD) connected via HDMI will lead to a drop in FPS.
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Old 07-10-2019, 01:31 AM   #2
y2kiah
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my CDU is built this way, some information here:
https://github.com/y2kiah/A-10C-CDU-Display

pictures of the build are posted in my thread here.
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Old 07-10-2019, 05:40 AM   #3
lesthegrngo
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That's really impressive, I'm certainly interested in more details of that - as it happens I had started a similar thread about TFT LCD screens with this very type of thing in mind.

If you have schematics you can share I would love to see them. I think I get it about the button matrix, I imagine it's similar to the LED matrix panel I am making for the CWP, but how that then connects into the Raspberry Pi is the mystery for me. I know I have one from a little TV box I bought for the wife to watch Netflix on a TV that didn't have network capability so I have some of the hardware already.

You also say that you made the buttons, which is another point I'd like to find out about. You can get square and round button caps on fleabay, but the smaller rectangular ones and the rocker type caps are ones I have so far been unsuccessful in finding. You have obviously managed to find a solution and despite your protestations I think they look great.

So, please do share, you've done a great job and I would love to be able to follow suit

Cheers

Les
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Old 07-11-2019, 12:22 PM   #4
y2kiah
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@lesthegrngo the button matrix connects to the Pi through a chip called the MCP23017, breakout boards for this chip can be found on ebay for under a dollar (U.S.). This connects to the Pi through the I2C bus, so it only takes a couple pins to run the whole matrix. The MCP chip gives you 16 inputs in 2 groups of 8, so that's 8 rows and 8 columns for 64 buttons. The other 3 buttons on the CDU are handled separately with direct input to RPi pins. The code for controlling the MCP chip and scanning the key matrix on the Pi is in this file, mostly right in the "main" function.

Regarding the buttons, I made them myself on my laser cutter out of several layers of acrylic sandwiched together and bonded by solvent. The problem with doing buttons this way is it's very laborious, and the results aren't very good. Laser cutters don't make a perfectly vertical cut through the material, so there can be a visible ridge between layers even if they are aligned perfectly. I try to mitigate that by alternating the pieces so wide edges meet other wide edges, and narrow edges meet narrow edges, but it is still a challenge to align them perfectly when bonding. The last challenge I found was that painting them to look good with back-lighting is actually a huge pain, you need to go much thicker with the paint than you might think, and there is no way to tell if your coverage is good without testing. I ended up making hundreds of touch-ups to all of my buttons with a brush and not-quite-perfectly-matching paint. In the end it looks good to the naked eye, and I am fine with the results, but when you get nice close-ups with a camera, you can really start to see all of the flaws in the buttons.

The next time around, I may try cutting over-sized pieces and then sanding them down to size. I will try painting the buttons by dipping them in paint instead of spraying.

Last edited by y2kiah; 07-11-2019 at 11:43 PM. Reason: edit
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Old 07-12-2019, 05:43 AM   #5
lesthegrngo
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Thanks. Interesting way of making the buttons, certainly food for thought for me. There are some off the shelf ones for the square and circular but they don't accommodate backlighting, but I think realistically in this case I have to look at the big picture and accept that while it may be nice, it would take too much time from other parts of it. Nonetheless it does help me with my project as it gives me some alternative ideas

Cheers

Les
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