LED average current (100mA) varies with temperature and component tolerances, an AC-bypassed current sense resistor is put in series with the LED. A feedback loop measures voltage on this resistor and keeps it at a preset level by varying supply voltage of the 74AC04 gates. Therefore, the nominally digital 74AC04 is operating as a structured power CMOS switch completely in analog mode. This way the LED junction is flooded and cleared of carriers as quickly as possible, basically by short circuit discharge. This pushes the speed of the LED to maximum, which makes the output optical signal fast enough so that the range/power ratio is the same as with the faster red HPWT-BD00-F4000 LED. The side effects of this brutal driving technique are: 1) the LED overshoots at the beginning of longer (5 MHz/1 MHz) impulses to about 2x brightness. This was measured to have no adverse effect on range. 2) A blocking ceramic capacitor bank backing up the 74AC04 switching array is crucial for correct operation, because charging and discharging the LED is done by short circuit. Under dimensioning this bank causes the leading and trailing edges of the optical output to grow longer. Transceiver – Ronja Twister Ronja Twister is an electronic interface for free space optical datalink based on counter and shift register chips. It is a part of the Ronja design. It is effectively an optical Ethernet transceiver without the optical drive part. The original design has been superseded with Twister2 but the logic circuit remained the same. Open source hardware approach Soderberg, studying Ronja sociologically, writes: "Arguably, the first project that vindicated the methods and licensing schemes of free software development, applied those practices to open hardware development, and pulled off a state-of-the-art technology without any backing from universities or firms, was the Ronja project." The whole toolchain is built strictly upon free tools and the source files are provided, free, under the GPL. This allows anyone to enter the development, start manufacture or invest into the technology without entry costs. Such costs normally can include software licence costs, time investment into resolution of compatibility issues between proprietary applications, or costs of intellectual property licence negotiations. The decision to conceive the project this way was inspired by observed organizational efficiency of Free Software. On Christmas 2001, Ronja became the world's first 10 Mbit/s Free Space Optics device with free sources. Examples of tools used in