Tag Archive | "COM-09032"

Tutorial: Video output from your Arduino

Create video output from your Arduino in chapter 35 of tutorials about the Arduino universe. The first chapter is here, the complete series is detailed here.

[Updated 10/01/2013]

In this chapter we will examine something different – the ability of our Arduino and compatible boards to create composite video output. In other words, displaying stuff from the Arduino on a TV. A lot of people were unaware of the ability to do this, however the process is very simple and not difficult to implement from a hardware perspective. Within this chapter we will learn to construct the minimum hardware required and demonstrate basic functions to get started.

To whet your appetite, here is a quick video demonstration of what is possible:

You can’t expect too much from a 16 MHz microcontroller without a video card… but the price is right, and with some imagination and the right functions you can do quite well. To make this happen we need to knock out some hardware of our own. Connection is very easy. First we need to locate three pins on our Arduino board. They will be used to output Sync, Video and also GND. For those with Arduino Uno/Freetronics Eleven etc Sync is digital 9, video is digital 7 and GND is … GND. If you have a Mega/Mega2560 Sync is digital 11 and video is A7. There is also the ability to generate audio with the methods in this article, and if you want to do this the Uno (etc.) pin is digital 11 or 10 on the Mega.

The monitor or television used needs to have a composite video-in socket (jack). For those with older televisions that have a VCR connected, you could use the video-in socket on the VCR. The schematic for video out is very simple, you only need two normal 0.25W resistors and a video lead:

If you’re not up for soldering into an RCA plug, a simple way is to chop up a standard video lead as such:

Then just wire the termination of the two resistors to the centre core (“pin”) and GND to the shield. For the purpose of this article I have made a quick TV-out shield that also includes a thumb joystick (as reviewed here).

A real triumph of engineering… however it solves the problem. The vertical trimmer is connected to A0;  the horizontal to A1; the button to digital 8 via a 10k0 pull-up resistor. Next, you will need to download and install the arduino-tvout library. It can be found here. We will use the TVoutBeta1.zip version.  Those of you who may have a nootropic design Hackvision – please note your library is different.

Now to see how to integrate TV-out into our sketch. We will run through the basic functions which integrated with your imagination should see some interesting results…  So let’s go!

For every project, place these two lines at the top of your sketch:

The first brings in the library, and the second line creates an instance of TV to use with the library functions. Next, we need to activate TVout and select the appropriate broadcast standard (PAL or NTSC). In void setup() use either

Now for the main functions. The first one of interest will be:

which … clears the screen. Or if you would like to fill the screen with white, use

Moving on – to write some text. First we need to select a font. There are three basic fonts to choose from:

  • font4x6 (each character being 4 pixels by 6 pixels, etc.)
  • font6x8
  • font8x8

Well there is four, but it wouldn’t display for me. Working on it! To choose a font use:

Then to write the text, choose the screen location with:

then display the text with:

You can also use TV.println(); to add a carriage return as expected. Display single characters with a position in the one function using:

So let’s have a look at the various fonts in action with the following sketch:

 

Now to move into the 1970s with some basic graphical functions. We have a screen resolution of 128 by 96 pixels to work with. When planning your display, you need to ensure that the sketch never attempts to display a pixel outside of the 128 x 96 screen area. Doing so generally causes the Arduino to reboot.

First let’s start with basic pixels. To draw a pixel, use:

where x and y are the coordinates of the pixel, and z is the colour (1 = white, 0 = black, 2 = inverse of current pixel’s colour). You want more than a pixel? How about a line:

Draws a line from x1, y1 to x2, y2 of colour colour. (1 = white, 0 = black, 2 = inverse of current pixel’s colour).

Rectangles? Easy:

Draws a rectangle with the top-left corner at x,y; width w, height h, colour and optional fill colour. Circles are just as simple:

Draws a circle with centre at x,y; radius r pixels, edge colour, optional fill colour.

Now to see these functions in action with the following sketch:

And for the video demonstration:

So there you have it, a start with Arduino and TV-out. Furthermore, a big thanks to http://code.google.com/u/mdmetzle/ for the arduino-tvout library.

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Have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, subscribe  for email updates or RSS using the links on the right-hand column, or join our Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

Posted in arduino, COM-09032, education, lesson, tutorial, tv out, videoComments (42)

Part review – Sparkfun Thumb Joystick

Hello readers

Today we examine an inexpensive yet fascinating little input device – the thumb joystick. Many people would recognise this as similar to the joystick in various types of gaming consoles, and they would be right. Let’s have a look:

joysticksmall

In the image above the joystick has been soldered into the matching breakout board. Unless you are making your own PCBs, you will want the breakout board:

bboard

The joystick consists of two 10k variable resistors, spring-loaded with centre return; also a SPST button that is activated by pushing down on the joystick:

joysticksidesmall

In order to use this joystick, we need an idea of the values that it can return. I have done this in three ways:

First of all, I connected a multimeter and measured the resistance of each axis. For the vertical axis, dead centre was 3.77k ohms, maximum up was 4.7k, with a maximum of 5.9k between centre and maximum – very odd. The vertical minimum was 83 ohms. For the horizontal, dead centre was  around 3.73k ohms, full left was 4.78k, via 5.38k; full right was 180 ohms without any odd high values in between. However, those values didn’t feel right.

Secondly,  I have recorded a visual representation of the horizontal and vertical axes’ effect on the supply voltage, using my little oscilloscope. With regards to the following two video clips, the supply voltage is 5V; the ‘scope display is set to 1V/division, with 0V at the bottom of the screen.

The horizontal axis:

and the vertical axis:

Finally, I connected the horizontal and vertical output to  analog inputs on my Arduino, and used analogRead() to see how the joystick returned analogRead() values. The following video clip demonstrates this using an LCD to display the values. Furthermore, here is the sketch used for the following demonstration: demo sketch.pdf

It would seem that there is a lot of ‘dead area’… postions where there is no change in reading, where one would assume there to be a change. Again, this can be programmed out in your sketch by a little calibration and measurement.

Now we know what values it returns, we can start to understand how to control things. When it comes to use the joystick in your own projects, it would pay to recreate a measurement circuit and note down the values your joystick returns; in order to be able to calibrate your software to use the joystick appropriately you may need to compensate for the hardware irregularities of the joystick.

Overall however, it is an interesting and easy product to integrate into your projects. This post today is just an introduction, later on the joysticks will be used in other projects and so on. High resolution photos are available on flickr. And if you enjoy my tutorials, or want to introduce someone else to the interesting world of Arduino – check out my new book “Arduino Workshop” from No Starch Press.

In the meanwhile have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, subscribe  for email updates or RSS using the links on the right-hand column? And join our friendly Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

Posted in arduino, BOB-09110, COM-09032, lesson, part review, thumb joystick, tutorialComments (11)


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