Single high-brightnessLED with a cheaploupe lens creates a bright narrow[1] beam that can streamDVD-quality video over neighbourhoods. The red beam is invisible when observed outside of its unobstructed path.Twibright Ronja with 130-millimetre (5.1 in) diameter lenses, operating on a 1,205-metre (1,318 yd) link using visible red light, max. range 1,300 metres (1,400 yd), with HPWT-BD00-E4000 transmitter LED. Installed on a rooftop, with its user posing to the right, in Czech Republic.[2][3]Three bolts preloaded with pink rubber blocks facilitate fine adjustment of the optical head direction with a gear ratio 1:300.[1] The bolt on the right side is a part of a rough adjustment mechanism which allows pointing the optical head in needed direction.Artificially enhanced picture of fog interfering with a RONJA beam, compromising the connection by introducinginterference
The basic configuration has a range of 1.4 km (0.87 mi). The device consists of a receiver andtransmitter pipe (optical head) mounted on a sturdy adjustable holder. Twocoaxial cables are used to connect the rooftop installation with a protocol translator installed in the house near acomputer orswitch. By increasing the diameter of thelens and transmitter pipe diameter, the range can be extended to 1.9 km (1.2 mi)[5].
Building instructions, blueprints, and schematics are published under theGNU Free Documentation License, with development using onlyfree software tools. The author calls this approach "User Controlled Technology", emphasising their view on the importance of open-source and user-driven software and innovation[6]
The building instructions are very detailed, guiding the builder along the setup. Basic operations likedrilling,soldering etc., are explained, along with all technical terms used.[7] Several techniques – drilling templates,[8] detailed checks after soldering,[9][10][11][12] testing procedures[13][14][15] – are employed to minimize errors at critical places and help to speed up work.Printed circuit boards are downloadable ready for manufacture, with instructions for afabrication house (PCB manufacturer).[16][17]
154 installations, located in multiple European countries and Brazil in South America have been registered into a gallery with partial descriptions, pictures and extra data.[2]
With the brightest variant ofLumileds HPWT-BD00-F4000 LED and 130 mm diameter cheap magnifying glass lenses, the range is 1.4 km (0.87 mi).[6][18] The dimmer but more affordable E4000 variant of HPWT-BD00 yields 1.3 kilometres (0.81 mi).[19] The speed is always 10 Mbit/s full duplex regardless of the distance.
As anFSO system it requires clearvisibility between the transmitter and receiver. If the beam is obscured in a way that introduces too muchnoise or fully obstructs it, the link will stop working. Typically, problems may occur during conditions ofsnow or densefog.[21][22] One device weighs 15.5 kg (34 lb)[1] and requires 70 hours of building time.[23] It requires an ability to set full duplex manually on the network card or switch to take advantage of full duplex,[24] since it doesn't supportautonegotiation.[1] Must be plugged directly into PC or switch using the integral 1 metre (3 ft 3 in) Ethernet cable.[1]
A complete RONJA system is made up of 2transceivers: 2 opticaltransmitters and 2 opticalreceivers. They are assembled individually or as a combination. The complete system layout is shown in theblock diagram.
Map showing the distribution of the 153 registered installations of RONJA as of 1 October 2007. Based on data found at theofficial RONJA website
The usual approach in FSO (Free Space Optics)preamplifiers is to employ atransimpedance amplifier. A transimpedance amplifier is a very sensitivebroadband high-speed device featuring afeedback loop. This fact means the layout is plagued with stability problems and special compensation ofPIN diodecapacitance must be performed, therefore this doesn't allow selection of a wide range of cheap PIN photodiodes with varying capacitances.
Ronja however uses a feedbackless design[9] where the PIN has a high workingelectrical resistance (100kilohms)[9] which together with the total input capacitance (roughly 8 pF, 5 pF PIN and 3 pF[25] inputMOSFETcascode) makes the device operate with apassband on a 6 dB/oct slope of low pass formed by PIN working resistance and total input capacitance.[26][27] The signal is then immediately amplified to remove the danger of contamination bysignal noise, and then a compensation of the 6 dB/oct slope is done by derivator element on the programming pins[28] of an NE592 video amplifier.[29][27] A surprisingly flat characteristic is obtained. If the PIN diode is equipped with 3 kΩ working resistor to operate in flat band mode, the range is reduced to about 30% due tothermal noise from the 3 kΩ resistor.
The HSDL4220infraredLED is originally unsuitable for 10 Mbit/s operation. It has abandwidth of 9 MHz,[30] where 10 Mbit/sManchester-modulated systems need bandwidth of around 16 MHz. Operation in a usual circuit with current drive would lead to substantial signal corruption and range reduction. Therefore, Twibright Labs developed a special driving technique consisting of driving the LED directly with 15-fold 74AC04 gate output in parallel with RF voltage applied current-unlimited directly to the LED through large capacitors.[31] As the voltage to keep the nominal 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[32] 74AC04 is operating as a structured powerCMOS switch completely in analog mode.
This way the LEDjunction is flooded and cleared ofcarriers as quickly as possible, basically byshort 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 drivingtechnique 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 blockingceramic 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.
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.[33]
The original design has been superseded with Twister2 but the logic circuit remained the same.[34]
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."[35]
The wholetoolchain is built strictly upon free tools[36] and thesource files are provided, free, under theGPL.[37] This allows anyone to enter the development, start manufacture or invest into the technology withoutentry costs. Such costs normally can includesoftware licence costs, time investment into resolution of compatibility issues between proprietary applications, or costs ofintellectual property licence negotiations. The decision to conceive the project this way was inspired by observed organizational efficiency ofFree Software.
On Christmas 2001, Ronja became the world's first 10 Mbit/s Free Space Optics device with free sources.[38]
^Soderberg, J. (2010). "Free Space Optics in the Czech Wireless Community: Shedding Some Light on the Role of Normativity for User-Initiated Innovations".Science, Technology, & Human Values.36 (4):423–450.doi:10.1177/0162243910368398.S2CID145786449.
