Blinkentree

Revision as of 09:15, 18 February 2011

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Blinkentree
We built our own blinking X-mas tree for the market in Strassen.
Meetings:	none
Type:	hardware
Tracker:	http://source.hacker.lu/projects/blinkentree
Status:	concluded
Members:
Contact Person:	slopjong (mail), prometheus (mail)
Tools
QrCode:

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Introduction

What is this flashing green fir tree all about?

As creative hackers, we thought it would be great to support the Christmas market of the commune of Strassen with something tiny, but creative. Result? The Blinkentree. A green fir tree, adorned with flashing LEDs representing the ornaments of a 'real' tree.

A big thanks to all of you folks who purchsed a Blinkentree and thus supported syn₂cat Hackerspace.

Hacky Christmas!

Assembling the kit

If you didn't buy a kit but an already assembled Blinkentree, you can continue here.

Otherwise, follow the next instructions to assemble your kit. We recommend first soldering the resistors, then the chip socket, and finally the LEDs because it's easier to start with small devices and finish up with the biggest ones.

1. The resistors all have the same value, and as they don't have a polarity it doesn't matter what direction they're put on the board.
   

   

   Place the resistors as shown here.
2. The chip socket has an indentation which must be oriented downwards.
   

   

   Chip direction. The indentation points downwards.
   

   

   Chip direction. The indentation points downwards.
3. The LEDs have a polarity. The longer leg is positive (+) and the shorter one is negative (-). Moreover, the LEDs have a flat spot on the negative side. The current flows from the positive to the negative so you have to pay attention while you assemble the kit, or else the Blinkentree won't work! You have to mount the LEDs as shown on the second picture (click to resize).
   

   

How to program it on your own?

The goal of our Blinkentree project was to create a christmas tree that you can reprogram. You can change the flashing patterns as you wish.

Those who have never programmed before might start getting cold feet, but fear not! Nothing is hard when you want to learn something new. This howto is intended for everyone, even (and especially) by those who are new to programming. If you come across stuff that's too unclear, shoot us a quick email (electronics[at]hackerspace.lu) and we will be glad to help you .

If you're completely new to the microcontroller world, there are essentially four steps to be followed.

1. Get the compiler tools
2. Write the program
3. Compile the program (compiling means turning it from "human" language into "machine" language)
4. Get the compiled program into the microcontroller

Get the compiler toolchain

Before we start writing the program we must install the compiler. A compiler is a program which reads your program text (source code) and turns it into machine code which is a series of instructions that the controller will execute later. One instruction could be "set pin 3 of port B to high". Thus you could switch on an LED.

A very common compiler is the GCC compiler which is part of the WinAVR (Windows) and CrossPack-AVR (Mac). You might already have guessed it, we are using the C language here.

Windows users download WinAVR and mac users should download CrossPack AVR instead.

If you downloaded the windows version, the installer will ask you to make an entry in the PATH variable. Be sure that the checkbox in the dialog is checked.

echo $PATH

In addition, on the Mac /usr/local/CrossPack-AVR/bin should be present. If not execute this in order to add it:

echo -e " \n \n export PATH=/usr/local/CrossPack-AVR/bin:$PATH" >> ~/.profile

Coding

For both Windows and Mac chose a good editor like Notepad++ or Programmers Notepad for Windows and TextWrangler for Mac.

Defining new flashing patterns for your Blinkentree is easy. Here is a sample code:

Save this code in the file main.c . Briefly, this program powers on and off all the LEDs by setting all output pins to HIGH (255 as value) or LOW (0 as value).

In the first two lines, one library for input/output (I/O) operations and one library for delay operations are included.

In line 4 you define the main (primary) function that will be executed by the Blinkentree as soon as it's powered on. Every C program always include a 'main'

The DDRD and DDRB variables are defined to configure the ports (a grouping of pins on the microcontroller) D and B which could be either as input or as output. DDR stands for Data Direction Register and the following letter A, B, C or D defines the port. We initialize both, DDRD and DDRB, with 0b11111111 which are binary numbers where each 1 stands for one pin of the port. 1 means that the pin is set as an output wheras a 0 would be used to configure the pin as an input.

By setting the port B to HIGH (255 = 0b11111111) in line 12 we turn on all the LEDs of that port. If you want to turn on only certain LEDs you have to set other values from the range 0 to 255 (0b00000000 to 0b11111111). For some more advanced pin settings ,read this tutorial. You can use the decimal-binary converter to convert decimal numbers into binary numbers and vice versa.

The 'while' loop is necessary in order to continue executing the flashing pattern. Otherwise the microcontroller would stop at the end of the main function. In other words the flashing pattern would be executed only one time. (In fact, a microcontroller must NEVER completely terminate the main loop, but that's a topic for another day.)

On Suhas's blog you find more information about the I/O operations.

The code the Blinkentree is shipped with can be found here.

Compiling and linking

When the coding is done, translate it into machine code by opening your terminal (shell, command line or also known as cmd on Windows) and changing into the directory where your code file is.

There you type:

avr-gcc -Wall -Os -std=c99 -DF_CPU=1000000 -mmcu=attiny2313 -c main.c -o main.o 
avr-gcc -Wall -Os -std=c99 -DF_CPU=1000000 -mmcu=attiny2313 -o main.elf main.o 
avr-objcopy -O ihex -R .eeprom main.elf main.hex 

These commands are the same for Mac and Windows. We assume that you are not (yet) interested in what those lines mean exactly, so don't worry about them now. You can read this tutorial later when you're more familiar with compiling.

If nothing went wrong you should have main.hex which is the translated code. If something did go wrong, it's almost certainly because of a small typo that you made. Go back and check very carefully everything you've typed. There's not that much to check, so don't lose heart now, you're almost done!

The generated hex file will be loaded into your microcontroller in the next step.

Flashing the microcontroller

Congratulations! You're not yet bored about this stuff :-)

Now it's getting a bit tricky. You need a programmer device to upload your code to the controller. We used the USBasp programmer which you can buy here. As the USBasp programmer is an open source project you can also build it yourself.

Important: If you buy the ATMega chip somewhere else it might be missing the required firmware. In this case you need another programmer to get the programmer firmware into yours so you'll probably run into the chicken-and-egg dilemma.

Mac and Linux users don't need any driver for the programmer but Windows users do. Download it here.

When you finally got a programmer, you need to solder a pin header on your board. Have a look at your tree, there are six holes that are reserved for this purpose. You can get such a pin header in any electronics store, for just a couple cents. In Luxembourg there are S.A.M., Secto and Schaller, and perhaps others we didn't think to mention. In Germany Reichelt and Conrad are well-known.

The pins from left to right are:

1. MOSI | 2. MISO | 3. SCK | 4. GND | 5. VTG | 6. RST

On the USBasp you have this connector:

Connect all the pins with the same name. On the programmer device there are three jumpers.

VERY IMPORTANT: If VTG of the programmer is connected with VTG of your Blinkentree and JP1 is set then your Blinkentree is powered by USB. Be sure there are no batteries in the battery holder and/or the switch is turned to off. If you don't connect it, you have to switch it on. JP2 is used to update the programmer firmware. Don't set it in the normal mode. JP3 slows down the programming clock. This allows to flash targets with an internal clock less than 1.5 MHz. As the Blinkentree uses the internal 1 MHz clock JP3 must not be set.

Go into your shell / command line and execute this

avrdude -c USBasp -p t2313 -U flash:w:main.hex -v -F

On a mac-- and probably under linux too-- you must execute it with sudo.

sudo avrdude -c USBasp -p t2313 -U flash:w:main.hex -v -F

Footnotes

1. ↑ /usr/local/CrossPack-AVR is just a symbolic link to /usr/local/CrossPack-AVR-20100115 or something like that.