Comments on: VGA Experiments 2

By: bod

bod — Mon, 10 Nov 2008 19:24:20 +0000

sweet mate! well done, i can’t wait to try it out!! i do however have a done of projects to finish, but i’ll see if i can give this a shot at the weekend.

yeah, the timer2 function will use 2 pwm outputs making them useless for other operations, but it is a small price to pay for nailing this!

congrats. ;O)

By: dwan

dwan — Mon, 10 Nov 2008 17:54:14 +0000

Hello bod,

I come back with good news ! I completely re-wrote my program. Now, it outputs very clean sync signals (with a tiny little bit of horizontal jitter, though). Pin 5 is HIGH when you can send video signal, so you can trig some other signal with it. All the sync thing is done in a timer interrupt, so you can put whatever you want in loop() without breaking the timing. On the other hand, I think that using timer2 may have broken the PWM on pins 11 & 3. The code is here : http://olb7.free.fr/arduino/syncInterrupt.pde

Have fun !

By: bod

bod — Sat, 08 Nov 2008 13:33:17 +0000

Hi Dwan,

i was just looking through your code, and to be honest my coding knowledge even in arduino is a little basic, but based on the timing standards for VGA you appear to be close! I’ve been trying to find the one i wrote, but have a nasty habit of not saving things with proper names, its there somewhere….

there is a russian guy who has VGA sync working with the atmega 168 chips, but he’s not using the arduino IDE. http://www.vga-avr.narod.ru/main.html
From what i understand the arduino system might not be able to handle the timing correctly. I tried to email him but never got a response, but i ended up butchering his code and came up with something that vaugely worked, so a step in the right direction at least.

let me know how you get on, i’d love to try it out with some circuits i have to avoid using the computers vga output.

cheers,

bod.

By: dwan

dwan — Sat, 08 Nov 2008 13:08:20 +0000

Hi again !
After some hours of sleep, i ‘m very close to my goal. Vsync is ok, the screen is slowly drifting upwards in 1 min cycle. Hsync was more tricky to debug, but its almost ok. I think I did not understood vga sync as well as i thought, as my Hsync was not running all the time. Thanks anyway for your great works on videosynths !

By: dwan

dwan — Tue, 04 Nov 2008 23:31:11 +0000

Oops, my comment seems too long… You can get my code here : http://olb7.free.fr/arduino/SyncPortManipulation.pde

By: dwan

dwan — Tue, 04 Nov 2008 23:22:49 +0000

Hi,
I’ve been reading your VGA experimentations with a lot of attention, since i’m trying to produce really simple graphics with my Arduino (plain colors, actually). I began with borrowing the sync signals from my computer and sending my own RGB signals via 3 PWM outputs. The result was what you described, scrolling lines of pulsing colors. The next try was sending a constant voltage, but it didn’t work : the color would only appear on the voltage’s rising edges. I then started to think about being more respectful of VGA timing, and I plan to dedicate another Arduino only to create sync signals, so below is my attempt. For some reasons, it doesn’t work. I checked my timing with an oscilloscope, and it seems to be pretty accurate. I get some jitter with the Hsync. Since I’ve read that you succeeded in writing a piece of code that works (more or less ), can you spot an error in mine, or can you show yours? Thanks !

// 640 * 480 @ 60Hz
// HSync : pin 7
// VSync : pin 6

//Vpulse, pin 6 à 0V
//Hold à 0V : théorique : 63,55 us
//Fin du Vpulse, pin 6 à 5V
//Front Porch V: théorique : 317,77 us
//Hpulse, pin 7 à 0V
//Hold a 0V : théorique : 3,81 us
//Fin du Hpulse, pin 7 à 5V
//Front Porch H : théorique : 635 ns
//Display Time : théorique : 25,422 us
//Back Porch H : théorique : 1,906 us
//Back Porch V : théorique : 1048 us

int i = 0; // count

void setup() // run once, when the sketch starts
{
DDRD |= B11000000; // it sets pins 2 to 7 as output without changing the value of pins 0 & 1, which are RX & TX
// 76543210