Laborlicht

Firmware for the Laborlicht from Das LABOR. The software presented here is just for the basic version of the Laborlicht without a CAN or RFM12 controller (those modifications are rarely seen outside of 'Das LABOR' anyway).

The Laborlicht is a small device featuring 18 ultra bright LEDs (6 for each primary color) to allow for atmospheric lighting. It is quite similar to the Fnordlicht, albeit smaller. It uses PWM on every color channel to approximate arbitrary colors given by the main program.

In its unmodified form, the firmware does a quick color test on startup, fading through all colors of the rainbow in 15 seconds. Subsequently, it slows down and fades to a color for two minutes and holds that color for one minute.

The colors are shown in the following order:

• red
• yellow
• green
• cyan
• blue
• purple
• white (well, sort of)

After reaching the white color, the Laborlicht fades to a random color (where each color channel has a minimum brightness of 25%) and starts over afterwards.

Build

Linux / UNIX

Package names are based on Debian/Ubuntu repositories. Please adapt the names according to your Linux distribution (or BSD for that matter).

• make (gmake on BSD)
• gcc-avr
• avr-libc
• binutils-avr
• avrdude

Windows

• AVR GCC toolchain for Windows, choose your poison:
  • WinAVR
    • already includes avrdude
    • straight forward download from SourceForge
    • project abandoned in 2010, therefore quite outdated (avr-gcc 4.3.3)
  • Atmel AVR Toolchain for Windows
    • avrdude is not included, so you need to get it elsewhere
    • homepage nags you with rather awkward registration process before download
    • actively maintained, therefore fairly up to date
• Cygwin(64)
  • please install the 'make' package within Cygwin
• libusb-win32 in case you want to use an USBasp programmer device with avrdude

Configure

Building the firmware should work out of the box. However, if you want to tune some compiler flags, just edit the 'Makefile' directly.

Compile

To build the actual image file, just type:

make

In case you build on BSD, just use 'gmake' instead of 'make'. This yields an 'image.hex' file which you can flash to your AVR device.

If you happen to use a USBasp programmer in conjunction with avrdude, you might want to try the make target 'flash'.

Your own fading effects

Implementing your own color fading effects should be straight forward. Just take a look at the 'main()' function. If you have at least some basic knowledge of C, you will get the idea.

To display an arbitrary color, just change the current brightness values of the three primary colors (e.g. dark yellow):

g_color[channel_red] = 127;
g_color[channel_green] = 127;
g_color[channel_blue] = 0;

There are eight predefined colors as well:

typedef enum color_preset_e {
    color_black,
    color_red,
    color_yellow,
    color_green,
    color_cyan,
    color_blue,
    color_purple,
    color_white,
    color_MAX /* not a color, just a boundary */
} color_preset_t;

You can set them with the 'set_color_preset()' function:

set_color_preset(color_preset_t preset);

You can also fade to a preset from the currently shown color using the following function:

color_fade_preset(color_preset_t preset, unsigned char steps, unsigned int t);

The value 'steps' is the number of intermediate steps between the current and the target color, the value 't' determines how long a step should last (in milliseconds). This example will cause the Laborlicht to fade to red in 255 steps over the course of one minute:

color_fade_preset(color_red, 255, 235);

To fade to a custom color, just fill up an array of three bytes and hand it over to this function:

color_fade(uint8_t *color, uint8_t steps, uint16_t delay);

Just like:

unsigned char my_color[] = {192 /*red*/, 64 /*green*/, 16 /*blue*/};
color_fade(my_color, 255, 235);

In case you're open for surprises, you can fade to a random color, too.

 color_fade_random(255, 235);

Implementation details

The Laborlicht is quite an old project with commits dating back to early 2006. After roughly ten years, the code was in a rather bad shape. It was not compatible with recent versions of avr-gcc and avr-libc anymore, because the way interrupt handlers are declared has changed over the years, amongst other things.

So here it is, a rewrite of the basic Laborlicht firmware. The PWM interrupts are now generated by the second 8 bit timer of the ATmega8, allowing for a tightly written interrupt handler. The latter is now implemented in AVR assembly and it is actually faster than the timing interrupt of the lowest brightness. The old code just conflated the first nine levels to the same brightness. With the new code, the refresh rate of the LEDs is roughly 80 Hz featuring 256 different brightness levels.

However, support for 8 MHz devices is gone (unless you can live with a refresh rate of 40 Hz), so you better resolder your board if you happen to have a different clock than 16 MHz.