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#42
Arduino generated VGA (color) signal - Complete!
Hey guys,
By the picture above we can notice that the problem with the black area was solved, and now, the entire screen is filled, so we can print on any corner (640x480 @ 60Hz). The problem was the interrupt function, the time of calling and returning was taking so much time for an ATmega328, I replace the functio call for an "if", checking the timer register all the time. When the timer gets a defined value (31.3KHz), the "if condition" is true and the line is printed. This way the program is not wasting time calling and coming back from the interrupt function.
Another problem was that only CRT monitors were understanding my signal. The problem was the voltage level, now I am using a resistor in series with a diode for R, B and G, forcing my TTL (5V) signal to become 0.7V, as VGA standards says, and any VGA monitor (including LCD and LEDs) can print the signal.
So, everything is solved now, and we can generate color VGA sinal.
Now, I will try to create a library intelligent enough to design shapes and letters, and maybe generate more colors.
Everything using just an Arduino UNO. :))
Here is the code I wrote. Enjoy! We are here to share.
If you are going to try this, you must know this too:
And this:
"VGA industry standard" 640x480 pixel mode
General characteristics
Clock frequency 25.175 MHz
Line frequency 31469 Hz
Field frequency 59.94 Hz
One line
8 pixels front porch
96 pixels horizontal sync
40 pixels back porch
8 pixels left border
640 pixels video
8 pixels right border
---
800 pixels total per line
One field
2 lines front porch
2 lines vertical sync
25 lines back porch
8 lines top border
480 lines video
8 lines bottom border
---
525 lines total per field
Be aware of turning your RGB signal off when sync pulsing.
And open your eyes for what the compiler is doing (or trying to do) when reading your code. A lot of time is wasted in many situations, and the non-repetitive ones are the most dangerous.
If your signal is not in perfect sync, the monitor will reject your signal.
Use the osciloscope to monitor all this things.
Good luck and count on me if you need help!
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Comment by Marcelo Rodrigues on April 4, 2012 at 3:11pm -
Guys,
The code was wrong because Ning had cut some characters, so I change it to a link: http://pastebin.com/F5Gnewm8
Now it is ok. :)
Enjoy!
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Comment by Simon Schvartzman on July 27, 2012 at 10:51am -
Marcelo, Congratulations, this is really awesome!
Have you made any progress with the library? I would really like to try the whole stuff..
Best! Simon
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Comment by Marcelo Rodrigues on July 27, 2012 at 11:21am
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Hello Simon!
Thank you! Yes, Ive made some progress. Take a look at the images bellow:
With the same code (few adaptations) I could print images in a TFT LCD too:
Unfortunatly, I didn't have time to write the library yet. As soon as I do it I will post here. But the max quality (pixels) I could do with VGA was like the image above.
The TFT is still slow. We can see a line running on the screen. But putting the entire image in the flash memory it become fast enough for a good image.
Soon I post more info. Ok?
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Comment by Simon Schvartzman on July 27, 2012 at 11:59am
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Thanks for your prompt answer. Well done job!
Any hint regarding the best/cheapest way to connect an Arduino to an HDMI enabled monitor/Tv? Just to show text and simple graphics...
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Comment by Marcelo Rodrigues on July 27, 2012 at 1:19pm
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Comment by Simon Schvartzman on July 28, 2012 at 8:47am
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Marcelo, thanks again for getting back to me. Unfortunatky this is not really what I'm looking for. The HDMI CEC let's you control a device but I want to use the monitor as the output device for the Arduino. I other words I want to use a Monitor instead od an LCD display as the output device.. Anyway many thanks...will keep searching (I have seen some solutions by connecting an Arduino to a Rapsbery PI)
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Comment by Marcelo Rodrigues on July 30, 2012 at 7:19am
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MMmmmmm... I understood. This is a very interesting chalenge.
Keep us informed about your progress. I will try to make some research here too, maybe I can help.
Good luck!
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Comment by Mark Lewental on August 29, 2012 at 6:29am
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Marcelo,
Awesome! I'm interested in trying what you've done and was wondering if you had posted a schematic for DB15 interface to the Arduino. Many thanks!
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Comment by Marcelo Rodrigues on August 29, 2012 at 7:04am
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Mark,
I will find time to design it using Eagle. Until there, take a look at the table in the beggining of this post, there you will find the pins names. You could connect it directly to the Arduino, but the problem is the RGB signal must be 0.7V, so you have to reduce the voltage level from 5V to 0.7V. You can do this using 2 resistors as resistive dividers.
Let me know if you still have questions. :)
Good luck!
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Comment by Mark Lewental on August 29, 2012 at 7:59am
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Marcelo,
Thank you for the fast response! I noticed in your pictures you used diodes as well as resistors. Any specific ones? Thanks again!!!
Mark
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