The BL4 tech-page
The sourcecode for BL4 beacons is still under development. A fully functional "beta" for AVR ATmega88 can be downloaded here below. The sourcecode will later be modified to fit the cheapest and physically smallest ATtiny MCU´s. The sourcecode is written for the Imagecraft C-compiler. Everything needed have been put in a single textfile. For those who don´t want to edit the project, compile it themselves or simply don´t know how to do it, there´s also a standard HEX-file that can be programmed directly into the ATmega88.
The most recent version (V1.3, Jan 8, 2013) measures the ambient light by reverse-biasing the LED and then transmits "WWW.BL4.EU" repetedly only when it´s dark enough to be clearly seen. The message is repeated every five seconds. Some effort have been spent on reducing the power consumption by using power reduction registers, sleep-modes and timer based delays with interrupts. In this version, the average current consumption at 3V is only about 100-200uA, the LED included. The AVR runs on it´s internal 1MHz RC-clock. All you need to get it running is a programmer, an ATmega48/88/168 or ATtiny24/44/84 AVR-chip, a 3-4.5V battery and an LED. Depending on type of LED it can be connected directly to the AVR without a series resistor. A "super-green" LED at aprox 625nm gives the highest efficiency due to eye sensitivity spectra. (it also looks very nice :-)
It´s my intention to port/optimize the sourcecode for the much smaller 8-pin ATtinys that cost about 0,5€. (the 6-pin AVR´s are a bit different creatures to program) Since there are also realy cheap PIC´s from Microchip it would be nice if one of the BL4-fans could help porting the code to PIC-assembler.
Text and concept by John Ahlberg, Stockholm, Sweden 2012