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Conclusion

So, finally the end of the project was in sight: my hardware worked, the software was able to show graphics on the LCD in splendid dual-color monochromes (duochromes?) and didn't eat up the complete CPU in the process. As a finishing touch, I modified it to display the IP-address of the Raspberry Pi on startup, and after that use libvncclient as the source for the graphics it displays. Libvncclient starts up in listen mode, so you can use any random vnc server to connect to it, after which the LED-display will display a portion of what's on the monitor of the connecting computer. That way, I wouldn't have to invent something to do presentations for the LED-screen myself.

It works pretty well, as you can see here. Even video makes it over the VNC link fairly unscathed. Unfortunately, in this film the refresh rate of the display manages to interfere with the shutter speed of the camera; the flickering you see here isn't really visible in real life.

As usual, the software is downloadable and it is licensed under the GPLv2, because the servoblaster sources I used was GPLv2 too.

So, now the easy part is done, I still need to do the hard part: fix a nice housing for the display so it looks presentable... I'll save that for another time.

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11 comments

Jonathan Andrews wrote at 16 Nov 2013, 18.41:

Very nice job. Your code is better than mine, I guess I will have to read up on DMA :-) Thanks, Jon (jonshouse.co.uk)

rigid wrote at 7 May 2013, 14.23:

Cool hack! For you it might be too late but others may want to checkout the niftyled project at http://wiki.niftylight.de - You just have to adapt a bit of plugin code since all the nasty coding work is already done. Then you can combine your display with other LED hardware and you're not limited to VLC. You can feed pixels with other stuff like gStreamer, various fileformats, cat/netcat etc.

GCL wrote at 28 Apr 2013, 1.55:

Hello! Ah! A DX4. I knew of them turning up into the commercial world. I hadn't realized that they did make it to the embedded market. But then again I didn't completely follow the I486 series, in favor of the I386 activities, and then of course the Pentium activities. As for what happened earlier, with your box, yes of course.

Jas wrote at 27 Apr 2013, 19.55:

For more flexibility, you could make it use the PixelPusher protocol: https://github.com/hzeller/rpi-matrix-pixelpusher Then it'll plug into all the PixelPusher software, including Processing.

Zmaster wrote at 27 Apr 2013, 13.04:

I particularly like the DMA hack to drive GPIOs. Great job overall, led panels are cool :) I'm not sure the flickering we see in the last video is related to the frame rate, those pixels around the text in the shell are never supposed to light up.

dans34 wrote at 27 Apr 2013, 6.56:

would you consider selling the industrial pc gtom the sign

Sprite_tm wrote at 27 Apr 2013, 5.09:

GCL: According to the BIOS-screen (in one of the pictures on the 2nd page of the article) it's a DX4. I don't think it 'switches to' the LEDs; I actually managed to crash whatever graphical system disables the console by sending random data to some TCP-port and the LEDs still worked after that.

GCL wrote at 27 Apr 2013, 4.32:

Interesting. A system running QNX and an I486DX too boot. Can you tell me if the thing is an Intel 486DX or Intel 486DX2? The big difference is that the DX2 can run faster, and possibly cooler. Now the interesting one is that of, what transportation system used it? If I understand the way the system works, from your notes, the system screen blanks because it switched to the display board, and thought it wouldn't need the system screen.

Sprite_tm wrote at 27 Apr 2013, 4.27:

500 Internal Server Error: Ahrg, it's always been there. I plead a terminal case of stupid; it's been corrected.

500 Internal Server Error wrote at 27 Apr 2013, 3.23:

The "tip jar" link is actually on the right hand of the screen in this current version of the website.

My name wrote at 26 Apr 2013, 23.34:

So Beautiful

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