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Author Topic: Turn your Uno into a VGA output device!  (Read 25918 times)
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After playing with the MicroVGA card, I was wondering if it was possible to simply output VGA video directly from the Uno?

And it turns out, yes it is ... see photo:



This is the result of quite a bit of research. It seems that a few other people have done something similar, which helps, because their research and examples were a big help.

However this is the first example, that I know of, that simply runs on an ordinary Uno, using the standard Arduino IDE (no assembler code).

The only additional hardware was:

  • 5 resistors
  • A DB15 socket to plug the VGA cable into
  • Wires to connect

There are some unavoidable limitations in trying to squeeze this sort of performance out of a small chip like this, such as:

  • Monochrome output
  • 20 characters wide by 30 characters deep (160 x 480 pixels)

But, hey, this is more data than you can show on a 2-line LCD screen, or even a 4-line one.

The chip is kept quite busy refreshing the screen ... there is a horizontal sync pulse every 32 uS, which means there isn't a heap of spare processing time. But I have set it up to receive "print" commands via I2C from another Uno. That way one can be doing the calculations, and the other the displays. You could have the one do the lot, but the screen might have to go blank, or flicker, if it was doing a lengthy computation. But still, for the cost of a $5 Atmega328 chip, this is still quite a cheap output device (assuming you have an old LCD monitor lying around).

I'm going to spend the next couple of days documenting how it works, posting code, and so on.
« Last Edit: April 21, 2012, 05:50:13 am by Nick Gammon » Logged


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For anyone keen to see the sketch, here it is:

http://gammon.com.au/Arduino/VGA_output.zip

You need the "timer helpers" library, available from here:

http://gammon.com.au/Arduino/TimerHelpers.zip
« Last Edit: April 20, 2012, 02:55:17 am by Nick Gammon » Logged


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Nice work Nick.

I'm very interested in this. I also found this: http://code.google.com/p/arduino-vgaout/ which has currently : 64x64 - 64colors
Maybe it can help you improve your code?

keep us informed.
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I didn't see any code in that link, but thanks for that!

(Edit) I spotted the code. smiley

His example of 64 x 64 pixels is a total of 4096. My screen shows 160 x 480 pixels which is a total of 76,800 pixels.

So there is a trade-off. For much fewer pixels you probably have time to output colour information.

I'll be documenting the design decisions, and how it all works. I found that time was extremely critical in trying to output even 20 characters (160 pixels) horizontally. For example, I had to restructure the font table in such a way as to save a single divide by 8 (or shift right 3 bits).

It's not even as if assembler would help. It takes 16 clock cycles to output 8 pixels, so you have a limited amount of time to work out what the next 8 pixels are going to be.
« Last Edit: April 20, 2012, 03:16:35 am by Nick Gammon » Logged


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Quote
His example of 64 x 64 pixels is a total of 4096. My screen shows 160 x 480 pixels which is a total of 76,800 pixels.

Yep I know, something in between would be nice ;-)

Would it be possible to blow up fonts, without the need of adding a bigger font? Let's say you have a 7x5 font could you make it 14x10? For my project I would need large fonts, but for now I had to change resolution to achieve this:
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Certainly you can make them larger. In my project I simply doubled the font vertically to make it look more reasonable because the horizontal drawing was a bit slow.
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Are you going to make a library? I would certainly use is. Right now I'm using SURE3208 dotmatrix panels and also a second ATMEGA just for rendering the displays. The first Arduino does all the other stuff and sends text buffers it to the second one over I2C, just as you are doing.

My CastDuino Shield (the second ATMEGA, use the same way you do, well sort of) has the code for connecting LCD, DOTMATRIX LED, VIDEO-out and needs VGA (microvga shield, doesn't play nice)
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Full description of this project with code, wiring, explanations, now here:

http://www.gammon.com.au/forum/?id=11608
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I managed to get colour output:



However memory is tight.

Sketch:

Code:
/*
 VGA colour video generation
 
 Author:   Nick Gammon
 Date:     22nd April 2012
 Version:  1.0
 
 Version 1.0: initial release

 Connections:
 
 D3 : Horizontal Sync (68 ohms in series) --> Pin 13 on DB15 socket
 D4 : Red pixel output (470 ohms in series) --> Pin 1 on DB15 socket
 D5 : Green pixel output (470 ohms in series) --> Pin 2 on DB15 socket
 D6 : Blue pixel output (470 ohms in series) --> Pin 3 on DB15 socket
 D10 : Vertical Sync (68 ohms in series) --> Pin 14 on DB15 socket
 
 Gnd : --> Pins 5, 6, 7, 8, 10 on DB15 socket


 Note: As written, this sketch has 34 bytes of free SRAM memory.
 
 PERMISSION TO DISTRIBUTE
 
 Permission is hereby granted, free of charge, to any person obtaining a copy of this software
 and associated documentation files (the "Software"), to deal in the Software without restriction,
 including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense,
 and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so,
 subject to the following conditions:
 
 The above copyright notice and this permission notice shall be included in
 all copies or substantial portions of the Software.
 
 
 LIMITATION OF LIABILITY
 
 The software is provided "as is", without warranty of any kind, express or implied,
 including but not limited to the warranties of merchantability, fitness for a particular
 purpose and noninfringement. In no event shall the authors or copyright holders be liable
 for any claim, damages or other liability, whether in an action of contract,
 tort or otherwise, arising from, out of or in connection with the software
 or the use or other dealings in the software.

*/

#include <TimerHelpers.h>
#include <avr/pgmspace.h>
#include <avr/sleep.h>

const byte hSyncPin = 3;     // <------- HSYNC

const byte redPin = 4;       // <------- Red pixel data
const byte greenPin = 5;     // <------- Green pixel data
const byte bluePin = 6;      // <------- Blue pixel data

const byte vSyncPin = 10;    // <------- VSYNC

const int horizontalBytes = 60;  // 480 pixels wide
const int verticalPixels = 480;  // 480 pixels high

// Timer 1 - Vertical sync

// output    OC1B   pin 16  (D10) <------- VSYNC

//   Period: 16.64 mS (60 Hz)
//      1/60 * 1e6 = 16666.66 uS
//   Pulse for 64 uS  (2 x HSync width of 32 uS)
//    Sync pulse: 2 lines
//    Back porch: 33 lines
//    Active video: 480 lines
//    Front porch: 10 lines
//       Total: 525 lines

// Timer 2 - Horizontal sync

// output    OC2B   pin 5  (D3)   <------- HSYNC

//   Period: 32 uS (31.25 kHz)
//      (1/60) / 525 * 1e6 = 31.74 uS
//   Pulse for 4 uS (96 times 39.68 nS)
//    Sync pulse: 96 pixels
//    Back porch: 48 pixels
//    Active video: 640 pixels
//    Front porch: 16 pixels
//       Total: 800 pixels

// Pixel time =  ((1/60) / 525 * 1e9) / 800 = 39.68  nS
//  frequency =  1 / (((1/60) / 525 * 1e6) / 800) = 25.2 MHz

// However in practice, it we can only pump out pixels at 375 nS each because it
//  takes 6 clock cycles to read one in from RAM and send it out the port.

const int verticalLines = verticalPixels / 16; 
const int horizontalPixels = horizontalBytes * 8;

const byte verticalBackPorchLines = 35;  // includes sync pulse?
const byte verticalFrontPorchLines = 525 - verticalBackPorchLines;

volatile int vLine;
volatile int messageLine;
volatile byte backPorchLinesToGo;

#define nop asm volatile ("nop\n\t")

// bitmap - gets sent to PORTD
// For D4/D5/D6 bits need to be shifted left 4 bits
//  ie. 00BGR0000

char message [verticalLines]  [horizontalBytes];

// ISR: Vsync pulse
ISR (TIMER1_OVF_vect)
  {
  vLine = 0;
  messageLine = 0;
  backPorchLinesToGo = verticalBackPorchLines;
  } // end of TIMER1_OVF_vect
 
// ISR: Hsync pulse ... this interrupt merely wakes us up
ISR (TIMER2_OVF_vect)
  {
  } // end of TIMER2_OVF_vect


void setup()
  {
 
  // initial bitmap ... change to suit
  for (int y = 0; y < verticalLines; y++)
    for (int x = 0; x < horizontalBytes; x++)
      message [y] [x] = (x + y) << 4;
   
  // disable Timer 0
  TIMSK0 = 0;  // no interrupts on Timer 0
  OCR0A = 0;   // and turn it off
  OCR0B = 0;
 
  // Timer 1 - vertical sync pulses
  pinMode (vSyncPin, OUTPUT);
  Timer1::setMode (15, Timer1::PRESCALE_1024, Timer1::CLEAR_B_ON_COMPARE);
  OCR1A = 259;  // 16666 / 64 uS = 260 (less one)
  OCR1B = 0;    // 64 / 64 uS = 1 (less one)
  TIFR1 = _BV (TOV1);   // clear overflow flag
  TIMSK1 = _BV (TOIE1);  // interrupt on overflow on timer 1

  // Timer 2 - horizontal sync pulses
  pinMode (hSyncPin, OUTPUT);
  Timer2::setMode (7, Timer2::PRESCALE_8, Timer2::CLEAR_B_ON_COMPARE);
  OCR2A = 63;   // 32 / 0.5 uS = 64 (less one)
  OCR2B = 7;    // 4 / 0.5 uS = 8 (less one)
  TIFR2 = _BV (TOV2);   // clear overflow flag
  TIMSK2 = _BV (TOIE2);  // interrupt on overflow on timer 2
 
  // prepare to sleep between horizontal sync pulses 
  set_sleep_mode (SLEEP_MODE_IDLE); 
 
  // pins for outputting the colour information
  pinMode (redPin, OUTPUT);
  pinMode (greenPin, OUTPUT);
  pinMode (bluePin, OUTPUT);
 
}  // end of setup

// draw a single scan line
void doOneScanLine ()
  {
   
  // after vsync we do the back porch
  if (backPorchLinesToGo)
    {
    backPorchLinesToGo--;
    return;   
    }  // end still doing back porch
   
  // if all lines done, do the front porch
  if (vLine >= verticalPixels)
    return;
   
  // pre-load pointer for speed
  register char * messagePtr =  & (message [messageLine] [0] );

  delayMicroseconds (1);
 
  // how many pixels to send
  register byte i = horizontalBytes;

  // blit pixel data to screen   
  while (i--)
    PORTD = * messagePtr++;

  // stretch final pixel
  nop; nop; nop;
 
  PORTD = 0;  // back to black
  // finished this line
  vLine++;

  // every 16 pixels it is time to move to a new line in our text
  if ((vLine & 0xF) == 0)
    messageLine++;
   
  }  // end of doOneScanLine

void loop()
  {
  // sleep to ensure we start up in a predictable way
  sleep_mode ();
  doOneScanLine ();
 }  // end of loop

Circuit:



(edit) Amended sketch slightly to add three "nop" instructions (no operation) after drawing the last pixel on the line. Without them, the final pixel is a bit narrow, as you can see in the photo.
« Last Edit: April 21, 2012, 09:06:36 pm by Nick Gammon » Logged


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Are you going to make a library?

You don't really need a library. Just load the "display VGA" text onto one processor, and do all the other work on the other one. A have a sample sketch on my web page that shows how you might send text from one to the other.
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Wow!

Well done, and very well explained! Although I don't quite yet understand it, but that's not your fault!

I have one question / bug report (maybe). I just had a look at the color VGA example. I haven't connected anything to an Arduino yet, just looked at it in the IDE. It compiles just fine (and at 1116 bytes!)

Of course from you screen photo and all it seems to work, but did you do some trick with this part (line 96-97)?
Code:
const byte verticalBackPorchLines = 35;  // includes sync pulse?
const byte verticalFrontPorchLines = 525 - verticalBackPorchLines;
It would seem that the byte "verticalFrontPorchLines" is truncated or wrapped around?
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Well spotted! You are right, that was an error on my part. In my defence however, that variable is never used ... it was just there for documentation (and being const, it doesn't use any memory). That's why it worked. smiley
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Do keep us updated on this...Wicked stuff, no doubt !!
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10 LET Loop=Infinite
20 GO TO 10

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Quote
I'm very interested in this. I also found this: http://code.google.com/p/arduino-vgaout/ which has currently : 64x64 - 64colors
I'm Nabe.
I'm glad that you were interested in my work.

That work started from here.
http://arduino.cc/forum/index.php/topic,76020.15.html
Sorry, I have been very busy so that project has been stopped.
I have not to do programing for several month.  smiley-cry
http://arduino.cc/forum/index.php/topic,76020.45.html

one clock resolition soft timer - it was able to achieve.
So, I drwew  "sine wave".
I had upped last version video before.
Sorry, the sound is too loud.


I have made some video signals with Arduino and registers.
http://www.youtube.com/user/MeowJapan/videos?sort=da&view=0
http://www.youtube.com/user/NabeRMC/videos?sort=da&view=0
To realize that it has a variety of techniques.
Many pepole generate many ways.
So It's intersting!
Limit the ability of Arduino seems to be beyond more than we think.

Let's enjoy with Arduino!

Thanks!
sorry I'm poor in English.




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Thanks for that! (I had to turn the music off, sorry).

I haven't done "moving" graphics yet but I thought a "pong" game would be interesting.

Quote
one clock resolition soft timer - it was able to achieve.

How did you do that?
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