RONJA

From Wikipedia, the free encyclopedia
  (Redirected from Ronja Twister)
Jump to: navigation, search
Single high-brightness LED with a cheap loupe lens creates a bright narrow[1] beam that can stream DVD-quality video over neighbourhoods. A few steps aside and the narrow beam becomes invisible.
Twibright Ronja with 130 mm (5 in) diameter lenses, operating on a 1205 m (0.75 mi) link using visible red light, max. range 1300 m (0.81 mi), with HPWT-BD00-E4000 transmit LED. Installed on a rooftop, with its user, 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.[4] The bolt on the right side is a part of a rough adjustment mechanism which allows pointing the optical head in virtually any direction.
Artificially enhanced picture of a situation where a Ronja link stops working because of heavy fog

RONJA (Reasonable Optical Near Joint Access) is a free-space optical communication system originating in the Czech Republic, developed by Karel Kulhavý of Twibright Labs and released in 2001. It transmits data wirelessly using beams of light. Ronja can be used to create a 10 Mbit/s full duplex Ethernet point-to-point link. It has been estimated that 1000 to 2000 links have been built worldwide [5]

The range of the basic configuration is 1.4 km (0.87 mi). The device consists of a receiver and transmitter pipe (optical head) mounted on a sturdy adjustable holder. Two coaxial cables are used to connect the rooftop installation with a protocol translator installed in the house near a computer or switch. The range can be extended to 1.9 km (1.2 mi) by doubling or tripling the transmitter pipe.

Building instructions, blueprints, and schematics are published under the GNU Free Documentation Licence. Only free software tools are used in the development. The author calls this level of freedom "User Controlled Technology".[6] Ronja is a project of Twibright Labs.

Manufacture[edit]

The building instructions are written with an inexperienced builder in mind. Basic operations like drilling, soldering etc., are explained.[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 the fabhouse.[16][17] People with no previous experience with building electronics have reported on the mailing list that the device ran on the first try.

154 installations worldwide have been registered into a gallery with technical data and pictures.[18]

Range[edit]

With the brightest variant of Lumileds HPWT-BD00-F4000 LED and 130 mm diameter cheap Chinese magnifying glass lenses, the range is 1.4 km.[19][20] The less bright, but easier to buy E4000 variant of HPWT-BD00 yields 1.3 km.[21] The speed is always 10 Mbit/s full duplex regardless of the distance.

Models[edit]

  • Ronja Tetrapolis: Range of 1.4 km (0.87 mi), red visible light. Connect with 8P8C connector into a network card or switch.
  • Ronja 10M Metropolis: Range of 1.4 km (0.87 mi), red visible light. Connects to Attachment Unit Interface.
  • Ronja Inferno: Range of 1.25 km (0.78 mi), invisible infrared light.
  • Ronja Benchpress: A measurement device for developers for physical measurement of lens/LED combination gain and calculation of range from that
  • Ronja Lopipe: The original (discontinued) design using red visible light and a RS232 interface for a max 115 kbit/s PPP/SLIP link.[22]

Limitations[edit]

By definition, clear visibility between the transmitter and receiver is essential. If the beam is obscured in any way, the link will stop working. Typically, problems may occur during conditions of snow or dense fog.[23][24] One device weighs 15.5 kg[25] and requires 70 hours of building time.[26] It requires an ability to set full duplex manually on the network card or switch to take advantage of full duplex,[27] since it doesn't support autonegotiation.[28] Must be plugged directly into PC or switch using the integral 1 m Ethernet cable.[28]

Technology[edit]

Block diagram of a full duplex RONJA system.

A complete RONJA system is made up of 2 transceivers: 2 optical transmitters and 2 optical receivers. They are assembled individually or as a combination. The complete system layout is shown in the block diagram.

Optical receiver - Preamplifier stage[edit]

Map showing the distribution of the 153 registered installations of RONJA as of 1 October 2007. Based on data found at the official RONJA website

The usual approach in FSO (Free Space Optics) preamplifiers is to employ a transimpedance amplifier. A transimpedance amplifier is a very sensitive broadband high-speed device featuring a feedback loop. This fact means the layout is plagued with stability problems and special compensation of PIN diode capacitance 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[29] where the PIN has a high working electrical resistance (100 kilohms)[30] which together with the total input capacitance (roughly 8 pF, 5 pF PIN and 3 pF[31] input MOSFET cascode) makes the device operate with a passband on a 6 dB/oct slope of low pass formed by PIN working resistance and total input capacitance.[32][33] The signal is then immediately amplified to remove the danger of contamination by signal noise, and then a compensation of the 6 dB/oct slope is done by derivator element on the programming pins[34] of an NE592 video amplifier.[35][36] 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 to thermal noise from the 3 kΩ resistor.

Optical transmitter - Nebulus infrared LED driver[edit]

The HSDL4220 infrared LED is originally unsuitable for 10 Mbit/s operation. It has a bandwidth of 9 MHz,[37] where 10 Mbit/s Manchester-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.[38] 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[39] 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[edit]

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.[40]

The original design has been superseded with Twister2 but the logic circuit remained the same.[41]

Use in Education[edit]

1 doctoral dissertation,[42] 10 master's and bachelor's theses [43] [44] [45] [46] [47] [48] [49] [50] [51] ,[52] 3 high school graduation exams [53] [54] [55] and 1 high school vocational activity [56] are based largely or completely on Ronja. Some of them present substantial changes, like underwater[52] or FPGA.[57][46] Further 4 doctoral dissertations [58] [59] [60] [61] , 18 master's and bachelor's theses [62] [63] [64] [65] [66] [67] [68] [69] [70] [71] [72] [73] [74] [75] [76] [77] [78] [79] , and 1 university semester project[77] cite Ronja.[80] Czech Technical University has built a 120 m educational link between the buildings of two faculties for teaching the students practically about FSO.[81][82] One Czech private university dedicates over a page of their textbook to Ronja.[83]

Additional 12 journal, conference and university articles are based largely on Ronja [84] [85] [86] [87] [88] [89] [90] [91] [92] [93] [94] .[95]

Open source hardware approach[edit]

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."[96]

The whole toolchain is built strictly upon free tools[97] and the source files are provided, free, under the GPL.[98] 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.[99]

Examples of tools used in development:

See also[edit]

Notes[edit]

  1. ^ Ronja Tetrapolis Specification - table row "Divergence cone half angle"
  2. ^ Gallery of Registered Installations line #7 Žďár nad Sázavou 1.205 km / 1.3 km
  3. ^ Ronja Installations gallery photo subdirectory - Czech Republic - Žďár nad Sázavou
  4. ^ Ronja Tetrapolis Specification - table row "Fine aiming gear ratio".
  5. ^ 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. doi:10.1177/0162243910368398. 
  6. ^ BRL-CAD: Ronja
  7. ^ Ronja: Fundamentals of Manufacturing Operations
  8. ^ All Ronja Drawings, showing many instances of drilling templates (with crosshairs and drill hole circles marked with drill diameter)
  9. ^ Building Ronja 10M Receiver - heading "Correctness check"
  10. ^ Building Ronja 10M Metropolis Transmitter - heading "Correctness checks"
  11. ^ Building Ronja Twister2 PCB - heading "Checking"
  12. ^ Building Ronja Nebulus - heading "Correctness check"
  13. ^ Testing Ronja Tetrapolis
  14. ^ Testing Ronja 10M Metropolis
  15. ^ Testing Ronja Inferno
  16. ^ Twister2 PCB
  17. ^ Ronja: Ordering TX PCB's
  18. ^ Registered Installations of Ronja
  19. ^ BRL-CAD: Ronja, mentioning the 1.4 km range
  20. ^ I. Rukovanský, M. Horváth, L. Solárik, P. Cícha: Computer Networks (in Czech), a university lecture textbook, European Polytechnic Institute - a Private University, 2015, mentioning the 1400 m range.
  21. ^ Ronja 10M Metropolis, Tetrapolis, Inferno, Rexlator distance issues - the official calculation graphs with source code, where the range of the individual LED and lens combinations can be looked up.
  22. ^ Linas Vepstas' Ronja mirror including the obsolete Ronja Loopipe building instructions
  23. ^ L Mustafa, B Thomsen (Department of Electronic & Electrical Engineering, University College London): Reintroducing Free-Space Optical Technology to Community Wireless Networks, Proceedings of the Nineteenth Americas Conference on Information Systems, Chicago, Illinois, USA, 2013.
  24. ^ Terence Bennett: Naval Applications for LiFi: The Transmitting Tool , Center for International Maritime Security, Maryland, USA, 2016.
  25. ^ Ronja Tetrapolis Specification, line "Weight"
  26. ^ How much does Ronja cost?
  27. ^ Ronja Tetrapolis: Requirements, heading "Software requirements"
  28. ^ a b Ronja Tetrapolis Technical Specification - table row "Data interface"
  29. ^ Building Ronja 10M Receiver - heading "Schematic", showing there is really no feedback in the signal path. The resistors and capacitors on the upper edge are power filter, they don't constitute a feedback.
  30. ^ Building Ronja 10M Receiver - heading "Schematic", R101 100k on the left edge of the schematic.
  31. ^ NXP Semiconductors: BF 908 Datasheet, page 2, table row "input capacitance at gate 1"
  32. ^ Phanumas Khumsat, Noppadol Wattanapisit, Karel Kulhavey, "Low-Cost Laser-Based Wireless Optical Transceiver for 10-Mbps Ethernet Link", Proceedings of IEEE Region 10 Conference (TENCON), Hong Kong, China (2006) (full text), pag 2 upper left, mention about "unwanted lossy integrator".
  33. ^ How does Ronja work? - heading "Photodiode".
  34. ^ Philips Semiconductors RF Communications Products: NE592 Product specification, page 1 lines 6-7 of the 1st paragraph and page 8, heading "FILTER NETWORKS".
  35. ^ Phanumas Khumsat, Noppadol Wattanapisit, Karel Kulhavey, "Low-Cost Laser-Based Wireless Optical Transceiver for 10-Mbps Ethernet Link", Proceedings of IEEE Region 10 Conference (TENCON), Hong Kong, China (2006) (full text)
  36. ^ Twibright Ronja: How does Ronja work?
  37. ^ HSDL-4220 Datasheet
  38. ^ Ronja Nebulus (infrared transmitter) schematic
  39. ^ Fairchild: 74AC04 Datasheet
  40. ^ Ronja Twister
  41. ^ Ronja Twister2
  42. ^ Johan Söderberg: Free software to open hardware: Critical theory on the frontiers of hacking, Doctoral Dissertation, University of Gothenburg, ISBN 9789197544276, Sweden, 2011.
  43. ^ David Němec: Cableless optical transmission (in Czech), Master diploma thesis, Institute of Telecommunications, Faculty of Electrical Engineering and Communication, Brno, Czech Republic, 2012.
  44. ^ Santi Phasuk (สันติ ผาสุข): Design and Implementation of a Data Transceiver via Visible Light Beam (in Thai with English abstract), Master Thesis, Kasetsart University, Bangkok, Thailand, 2011.
  45. ^ B. Bakala: Realization of Optical Link, Bachelor project, Department of Telecommunication Engineering, Czech Technical University, Prague, Czech Republic, 2011.
  46. ^ a b Jan Matyáš: FPGA-Based Ronja Twister (full text), Bachelor's Thesis, Department of Computer Systems, Faculty of Information Technology, Brno University of Technology, Czech Republic, 2011.
  47. ^ Bc. Lukáš Chobot: Wireless data transfer via optical modules (in Czech), Diploma Thesis, Faculty of Applied Computer Science, Tomas Bata University, Zlín, Czech Republic, 2011.
  48. ^ Bc. Filip Němec: Optical Cableless Transmittion (in Czech), Master's Thesis, Department of Telecommunications, Faculty of Electrical Engineering and Communication, Brno University of Technology, Czech Republic, 2010.
  49. ^ T. Szabo: Design and realization of wireless optical connection RONJA (mentioned in annual report), Master thesis, Department of Telecommunications, Faculty of Electrical Engineering and Information, Slovak University Of Technology in Bratislava, Slovakia, 2007.
  50. ^ Bc. Ľubomír Adámek: Wireless Data Transmission (in Czech), Diploma Thesis, Faculty of Applied Computer Science, Tomas Bata University, Zlín, Czech Republic, 2006.
  51. ^ Libor Štěpán: Wireless Optical Link for LAN Ethernet (in Czech), Bachelor Thesis, Faculty of Applied Computer Science, Tomas Bata University, Zlín, Czech Republic, 2006.
  52. ^ a b M. A. Chancey: Short Range Underwater Optical Communication Links (full text), Master Thesis, North Carolina State University, USA, 2005.
  53. ^ Petr Sádecký: High School Practical Graduation Exam: An Optical Datalink (in Czech), Electrotechnical Vocational High School SPŠE/VOŠ Karla IV. 13, Pardubice, Czech Republic, 2005,
  54. ^ Filip Němec: High School Practical Graduation Exam: An Optical Datalink Between Two Computers „RONJA 10Mb/s“ (in Czech), Electrotechnical Vocational High School SPŠE/VOŠ Karla IV. 13, Pardubice, Czech Republic, 2005,
  55. ^ Vojtěch Čižinský: Optical datalink transmitting 10 Mb/s (in Czech), High School Graduation Exam Technical Documentation, Electrotechnical Vocational High School SPŠE/VOŠ, Pardubice, Czech Republic, 2004.
  56. ^ Antonín Slováček, Petr Severa: RONJA – an optical datalink (in Czech, listing, result listing), High School Vocational Activity, Electrotechnical Vocational High School SPŠE Kounicova 16, Brno, Czech Republic, 2007.
  57. ^ Jan Matyáš (Faculty of Information Technology Brno University of Technology, Czech Republic): FPGA-Based RONJA Twister, ACM Student Project of the Year 2011 Competition, Information Sciences and Technologies Bulletin of the ACM Slovakia, Special Section on the ACM Student Project of the Year 2011 Competition, Vol. 3, No. 4, pp. 43-44, 2011.
  58. ^ Julio Francisco Rufo Torres: Contribution to the study of Services Supported on VLC (Visible Ligth Communications) Networks (in Spanish), Doctoral Thesis, Doctoral Program Cybernetics and Telecommunication, University of Las Palmas de Gran Canaria, University Institute for Technological Development and Innovation in Communications, 2015.
  59. ^ Stefan Jeu Sjraar Verhaegh: How Community Innovation Works - a Material-Semiotic Analysis of the Wireless Leiden Wi-Fi Network Doctoral Dissertation, University of Twente, Netherlands, 2010.
  60. ^ Charoen Tangtrongbenchasil, " Ubiquitous Optical Wireless Communication Using Optical Micro-Cell System ", Doctoral dissertation, Kochi University of Technology, Japan, 2008.
  61. ^ Christian Herzog, "K1-yNayTa1-xNbxO3 Thin Films for Integrated Electro-Optics" , Doctoral Dissertation No. 17275, Swiss Federal Institute of Technology in Zurich, Switzerland, 2007.
  62. ^ Stefano Truzzi: Visible Light Communication, Master Thesis, University of Turin, Italy, 2016.
  63. ^ Md Arifur Rahman: Routing on Resource Allocation in Free Space Optical Network, Diploma Thesis, Department of Science and Technology, Linköping University, Sweden, 2016.
  64. ^ Philip McGillis Bain: "Alternative Models of Connectivity: Reclaiming Networked Spaces", Master Thesis, University of Denver, Colorado, USA, 2015.
  65. ^ S. Ambady, M. Bredes, C. Nguyen: Visible Light Communication, A Major Qualifying Project Report completed in partial fulfillment of the requirements for the degree of Bachelor of Science, Worcester Polytechnic Institute, Worcester, Massachusetts, USA, 2015.
  66. ^ Marko Čaljkušić: Visible light communications (in Croatian), Undergraduate dissertation, Faculty of Electrical Engineering, Mechanical Engineering and Naval Architecture, University of Split, Croatia, 2015.
  67. ^ Pekka Kamsula: Design and Implementation of a Bi-directional Visible Light Communication Testbed, Master’s Thesis, Department of Electrical and Information Engineering, University of Oulu, Finland, 2015.
  68. ^ Michele Pittoni: Advanced Topology Analysis in Three Wireless Community Networks, Final Thesis Degree Course in Computer Science University of Trento Italy, 2014.
  69. ^ Jiří Haňka: Wireless Optical Link (in Czech), Bachelor's Thesis, Department of Radio Electronics, Faculty of Electrical Engineering and Communication, Brno University of Technology, Czech Republic, 2013.
  70. ^ Ondřej Vitvar: Analysis and Modification of a High School Network (in Czech), Bachelor Thesis, Faculty of Computer Science, Masaryk university, Brno, Czech Republic, 2013.
  71. ^ Frederik Scheire, David Schouppe: Design of a NRZ gigabit optical receiver with qualization for PCS fiber, Master Dissertation submitted to obtain the academic degree of Master of Science in Electrical Engineering, Department of Information Technology, Faculty of Engineering and Architecture, Ghent University, Belgium, 2012.
  72. ^ Rysakis Ioannis: Implementation of a Free Space Optics transceiver (in Greek), Bachelor Thesis, Department of Electronics, Technological Educational Institute of Crete, Greece, 2012.
  73. ^ Radek Janečka: Using Light for Communication and Measurement, Bachelor's Thesis, Pardubice University, Faculty of Electrical Engineering and Computer Science, Czech Republic, 2012.
  74. ^ Bc. Leoš Kaňa: Indoor Optical Wireless Link Design, Master's thesis, Brno University of Technology, Faculty of Electrical Engineering and Communication, Department of Radio Electronics, Brno, Czech Republic, 2011.
  75. ^ Bc. Jaroslav Horák: Optical Connection (In Czech language) , Master's Thesis in Department of Telecommunications, Faculty of Electrical Engineering and Communication, Brno University of Technology, Brno, Czech Republic, 2009
  76. ^ Filip Roth: Methods of optical Communication for Embedded Systems, Bachelor Thesis, Faculty of Informatics, Masaryk University, Brno, Czech Republic, 2008.
  77. ^ a b Pedro López Estepa: Underwater Optical Communication, Semester Project, Swiss Federal Institute of Technology in Lausanne, Switzerland, 2008.
  78. ^ J. A. Simpson: A 1 Mbps underwater communications system using LEDs and photodiodes with signal processing capability, Master's Thesis, Graduate Faculty of North Carolina State University , North Carolina, USA, 2007.
  79. ^ Lubomír Buben: A Simple GIS, Bachelor's Thesis, Czech Technical University, Faculty of Electrical Engineering, Prague, Czech Republic, 2007.
  80. ^ Ronja: Publications coauthored and citations citing Ronja
  81. ^ root.cz: Blue Twibright Ronja: an educational link installation on the Czech Technical University (in Czech)
  82. ^ Bakala, Lafata, CTU: Improving the Functionality of Free-Space Optical Link (in Czech with English abstract).
  83. ^ I. Rukovanský, M. Horváth, L. Solárik, P. Cícha: Computer Networks (in Czech), a university lecture textbook, European Polytechnic Institute - a Private University, 2015, pages 66-67
  84. ^ Sung Yub Yu, Se Bong Jang, Suk Chan Kim: Implementation of Visible Light Communication system for Real Time Video Transmission, Pusan National University, South Korea, 2016.
  85. ^ Johan Söderberg: Users in the Dark: The Development of a User-Controlled Technology in the Czech Wireless Network Community , in: Hacking Europe: From Computer Cultures to Demoscenes, pages 219-239, Springer London, DOI 10.1007/978-1-4471-5493-8_10, ISBN 978-1-4471-5493-8, 2014.
  86. ^ P. Lafata, B. Bakala: Designing and realization of free-space optical link and its diagnostic, Mechatronika, 2012 15th International Symposium, Czech Republic, ISBN 978-1-4673-0979-0, 2012.
  87. ^ P. Lafata, B. Bakala: Diagnostic and Remote Monitoring of FSO Link (in Czech), Czech Technical University, Faculty of Electrical Engineering, Department of Telecommunication Engineering, Czech Republic, 2011.
  88. ^ P. Lafata, B. Bakala: Improving the Functionality of Free-Space Optical Link., Czech Technical University, Faculty of Electrical Engineering, Department of Telecommunication Engineering, Czech Republic, 2010.
  89. ^ Filip Němec, Miloslav Filka: Optical Wireless Transmission in Laboratory , Department of Telecommunications, Brno University of Technology, Brno, Czech Republic, 2011.
  90. ^ P. Mišenčík, J. Turán, Ľ. Ovseník: Experimental FSO system RONJA for 625 nm (Experimentálny systém FSO pre 625nm RONJA, in Czech), page 22, Proceeding of the Faculty of Electrical Engineering and Informatics of the Technical University Košice, Technical University Košice, Slovak Republic, 2011.
  91. ^ Johan Söderberg (University of Gothenburg, Department of Sociology and work science): Free Space Optics in the Czech Wireless Community: Shedding Some Light on the Role of Normativity for User-Initiated Innovations, in Science, Technology & Human Values 36, ISSN 0162-2439, Sweden, 2011.
  92. ^ P. Lafata, B. Bakala: Low Cost Free-Space Optical System and Its Application , 23rd Conference and Exhibition on Optical Communications 2011-Scientific Section Proceedings, p. 48-51. Agentura Action M, Czech Republic, 2011.
  93. ^ J. Vodrážka, J. Hrad: Experiment with Simple Prototype for Visible Light Communication , 23rd Conference and Exhibition on Optical Communications 2011-Scientific Section Proceedings, p. 59-61. Agentura Action M, Czech Republic, 2011.
  94. ^ Jan Matyáš (Faculty of Information Technology Brno University of Technology, Czech Republic): FPGA-Based RONJA Twister , ACM Student Project of the Year 2011 Competition, Information Sciences and Technologies Bulletin of the ACM Slovakia, Special Section on the ACM Student Project of the Year 2011 Competition, Vol. 3, No. 4, pp. 43-44, 2011.
  95. ^ Johan Söderberg (University of Gothenburg, Department of Sociology and work science): Reconstructivism versus critical theory of technology: Alternative perspectives on activism and entrepreneurship in the Czech wireless community , in Social Epistemology, 24: 4, 239 — 262, Sweden, 2010.
  96. ^ Söderberg, Johan. 2013. "How open hardware drives digital fabrication tools such as the 3D printer". Internet Policy Review 2 (2). DOI: 10.14763/2013.2.138.
  97. ^ Twibright Ronja: Software used for Ronja development
  98. ^ Ronja: All Schematics
  99. ^ Slashdot Dec 22, 2001: Build Your Own 10Mbit /sec Optical Data Link
  100. ^ Schematic capture 
  101. ^ PCB, gEDA Project 

References[edit]

External links[edit]