DOCSLIB.ORG

Analyse Und Entwicklung Optischer Trackingverfahren Für Das Dreidimensionale Skizzieren in Der Virtuellen Produktentwicklung

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Analyse Und Entwicklung Optischer Trackingverfahren Für Das Dreidimensionale Skizzieren in Der Virtuellen Produktentwicklung Analyse und Entwicklung optischer Trackingverfahren für das dreidimensionale Skizzieren in der virtuellen Produktentwicklung Masterarbeit Vorgelegt an der Fachhochschule Köln Campus Gummersbach Im Studiengang Medieninformatik Ausgearbeitet von: Dipl.‐Ing.(FH) Patrick Tobias Fischer Erster Prüfer: Prof. Dr. rer. nat. Wolfgang Konen Zweiter Prüfer: Dipl.‐Inform. Johann Habakuk Israel Berlin, 17. April 2008 Inhaltsverzeichnis Inhaltsverzeichnis ........................................................................................................................................ 1 Kurzdarstellung der Arbeit ............................................................................................................................ 4 Abbildungsverzeichnis ................................................................................................................................... 5 Tabellenverzeichnis ....................................................................................................................................... 9 Akronyme und Glossar ................................................................................................................................ 10 1 Einleitung und Aufbau der Arbeit ....................................................................................................... 13 2 Einführung in das Thema..................................................................................................................... 16 3 Produktentwicklungsprozesse ............................................................................................................ 20 3.1 Der schöpferisch kreative Prozess in der Entwicklung .................................................................... 20 3.2 Kreativität und Innovation .............................................................................................................. 28 3.3 Die 3D‐Skizze und ihre weiteren Rollen im Entwicklungsprozess ................................................... 31 4 Stand der Wissenschaft und Technik .................................................................................................. 33 4.1 Virtuelle Realität .............................................................................................................................. 33 4.2 Interaktion in immersiven Umgebungen ........................................................................................ 36 4.2.1 3D Interfaces ....................................................................................................................... 39 4.2.2 3D Displays .......................................................................................................................... 40 4.3 Tangible User Interfaces und ihre Vorteile gegenüber herkömmlichen Benutzerschnittstellen ... 41 5 Methodik zum praktischen Teil der Arbeit ......................................................................................... 46 6 Dreidimensionales Skizzieren in der Cave mit SketchApp .................................................................. 48 6.1 Allgemeine Anforderungen zum 3D‐Skizzieren ............................................................................... 48 6.2 Funktionale Anforderungen an SketchApp ..................................................................................... 49 6.3 Interaktionsraum CAVE ................................................................................................................... 51 6.4 3D‐Skizzierwerkzeuge (TUIs) ........................................................................................................... 52 1 6.5 Schwächen des aktuellen Skizziersystems ...................................................................................... 54 7 Experimente (Analyse) ........................................................................................................................ 56 7.1 Maximale Handgeschwindigkeiten ................................................................................................. 56 7.2 Mittlere Handgeschwindigkeiten beim 3D‐Skizzieren .................................................................... 59 7.3 Betrachtung verschiedener Räume der Cave .................................................................................. 64 7.3.1 Wahrnehmungsraum des Anwenders in Bezug zur CAVE .................................................. 65 7.3.2 Analyse des tatsächlichen Interaktionsraum der CAVE ...................................................... 66 8 Ergänzung der 3D‐Skizzieranwendung durch optisches Tracking ....................................................... 69 8.1 Bestehende Systeme ....................................................................................................................... 69 8.2 Hardware ......................................................................................................................................... 71 8.2.1 Kamera, Objektiv und IR Setup ........................................................................................... 73 8.2.2 Der Marker (Target, Fiducial) .............................................................................................. 78 9 Allgemeine Schritte des Trackings ...................................................................................................... 86 9.1 Kamerakalibrierung ......................................................................................................................... 89 9.2 Entzerrung der Bildebene ............................................................................................................... 90 9.3 Kamerakalibrierung in Bezug auf Opti‐ und StereoTracker ............................................................ 92 9.4 Ermittlung und Tracking von distinkten Bildmerkmalen ................................................................. 92 9.4.1 Color Blob Tracking via Meanshift/Camshift ....................................................................... 93 9.4.2 Blobdetection ...................................................................................................................... 95 9.4.3 Ergebnis ............................................................................................................................... 96 9.5 Pose Estimation ............................................................................................................................... 98 9.5.1 Stereoskopische Pose Estimation ........................................................................................ 99 9.5.2 Monoskopische Pose Estimation ...................................................................................... 100 9.5.3 POSIT als mögliche Lösung zur Pose Estimation ............................................................... 101 9.5.4 SoftPOSIT ........................................................................................................................... 102 9.6 Identifikation der Marker .............................................................................................................. 103 9.6.1 3D‐2D‐3D Korrespondenz ................................................................................................. 103 2 9.6.2 Identifikation eines Multipunktmarkers ........................................................................... 103 10 Testimplementierungen für die Skizzieranwendung .................................................................... 105 10.1 Bild‐Akquisition ............................................................................................................................. 106 10.2 Stereoskopisches Tracking – StereoTracker .................................................................................. 107 10.2.1 Testimplementierung zur Epipolargeometrie ................................................................... 107 10.2.2 Triangulation ..................................................................................................................... 108 10.3 Monoskopisches Tracking – Optitrack .......................................................................................... 109 10.3.1 POSIT ................................................................................................................................. 109 10.3.2 SoftPOSIT ........................................................................................................................... 110 11 Ergebnisse und Diskussion ............................................................................................................ 111 12 Zukünftige Arbeit und Ausblick ..................................................................................................... 112 13 Schlusswort ................................................................................................................................... 113 3 Kurzdarstellung der Arbeit Das Entwerfen mit Stift und Papier ist nach wie vor eine weit verbreitete Methode in den frühen Phasen des Designs in den Domänen der Produktentwicklung, Konstruktion und Architektur; und dies, obwohl die digitale Technologie längst in allen anderen Arbeitsprozessen Einzug erhalten hat. Auch die frühen Phasen der Entwicklung sollen durch Informationstechnologien profitieren können. Neue Benutzerschnittstellen werden derzeit entwickelt, als eine Möglichkeit schnelle, intuitive Skizzen mit den Vorteilen der digitalen Technologie zu verbinden. Dazu gehört die Idee, das zweidimensionale Zeichenpapier um eine weitere
Load more

Recommended publications
  • A Review About Augmented Reality Tools and Developing a Virtual Reality Application
    Academic Journal of Science, CD-ROM. ISSN: 2165-6282 :: 03(02):139–146 (2014) $5(9,(:$%287$8*0(17('5($/,7<722/6$1' '(9(/23,1*$9,578$/5($/,7<$33/,&$7,21%$6('21 ('8&$7,21 0XVWDID8ODVDQG6DID0HUYH7DVFL )LUDW8QLYHULVLW\7XUNH\ Augmented Reality (AR) is a technology that gained popularity in recent years. It is defined as placement of virtual images over real view in real time. There are a lot of desktop applications which are using Augmented Reality. The rapid development of technology and easily portable mobile devices cause the increasing of the development of the applications on the mobile device. The elevation of the device technology leads to the applications and cause the generating of the new tools. There are a lot of AR Tool Kits. They differ in many ways such as used methods, Programming language, Used Operating Systems, etc. Firstly, a developer must find the most effective tool kits between them. This study is more of a guide to developers to find the best AR tool kit choice. The tool kit was examined under three main headings. The Parameters such as advantages, disadvantages, platform, and programming language were compared. In addition to the information is given about usage of them and a Virtual Reality application has developed which is based on Education. .H\ZRUGV Augmented reality, ARToolKit, Computer vision, Image processing. ,QWURGXFWLRQ Augmented reality is basically a snapshot of the real environment with virtual environment applications that are brought together. Basically it can be operated on every device which has a camera display and operation system.
    [Show full text]
  • Virtual and Augmented Reality
    Virtual and Augmented Reality Virtual and Augmented Reality: An Educational Handbook By Zeynep Tacgin Virtual and Augmented Reality: An Educational Handbook By Zeynep Tacgin This book first published 2020 Cambridge Scholars Publishing Lady Stephenson Library, Newcastle upon Tyne, NE6 2PA, UK British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Copyright © 2020 by Zeynep Tacgin All rights for this book reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the copyright owner. ISBN (10): 1-5275-4813-9 ISBN (13): 978-1-5275-4813-8 TABLE OF CONTENTS List of Illustrations ................................................................................... x List of Tables ......................................................................................... xiv Preface ..................................................................................................... xv What is this book about? .................................................... xv What is this book not about? ............................................ xvi Who is this book for? ........................................................ xvii How is this book used? .................................................. xviii The specific contribution of this book ............................. xix Acknowledgements ...........................................................
    [Show full text]
  • Augmented Reality, Virtual Reality, & Health
    University of Massachusetts Medical School eScholarship@UMMS National Network of Libraries of Medicine New National Network of Libraries of Medicine New England Region (NNLM NER) Repository England Region 2017-3 Augmented Reality, Virtual Reality, & Health Allison K. Herrera University of Massachusetts Medical School Et al. Let us know how access to this document benefits ou.y Follow this and additional works at: https://escholarship.umassmed.edu/ner Part of the Health Information Technology Commons, Library and Information Science Commons, and the Public Health Commons Repository Citation Herrera AK, Mathews FZ, Gugliucci MR, Bustillos C. (2017). Augmented Reality, Virtual Reality, & Health. National Network of Libraries of Medicine New England Region (NNLM NER) Repository. https://doi.org/ 10.13028/1pwx-hc92. Retrieved from https://escholarship.umassmed.edu/ner/42 Creative Commons License This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 4.0 License. This material is brought to you by eScholarship@UMMS. It has been accepted for inclusion in National Network of Libraries of Medicine New England Region (NNLM NER) Repository by an authorized administrator of eScholarship@UMMS. For more information, please contact [email protected]. Augmented Reality, Virtual Reality, & Health Zeb Mathews University of Tennessee Corina Bustillos Texas Tech University Allison Herrera University of Massachusetts Medical School Marilyn Gugliucci University of New England Outline Learning Objectives Introduction & Overview Objectives: • Explore AR & VR technologies and Augmented Reality & Health their impact on health sciences, Virtual Reality & Health with examples of projects & research Technology Funding Opportunities • Know how to apply for funding for your own AR/VR health project University of New England • Learn about one VR project funded VR Project by the NNLM Augmented Reality and Virtual Reality (AR/VR) & Health What is AR and VR? F.
    [Show full text]
  • Augmented Reality for Unity: the Artoolkit Package JM Vezien Jan
    Augmented reality for Unity: the ARToolkit package JM Vezien Jan 2016 ARToolkit provides an easy way to develop AR applications in Unity via the ARTookit package for Unity, available for download at: http://artoolkit.org/documentation/doku.php?id=6_Unity:unity_about The installation is covered in: http://artoolkit.org/documentation/doku.php?id=6_Unity:unity_getting_started Basically, you import the package via Assets--> Import Package--> custom Package Current version is 5.3.1 Once imported, the package provides assets in the ARToolkit5-Unity hierarchy. There is also an additional ARToolkit entry in the general menu of unity. A bunch of example scenes are available for trials in ARToolkit5-Unity-->Example scenes. The simplest is SimpleScene.unity, where a red cube is attached to a "Hiro" pattern, like the simpleTest example in the original ARToolkit tutorials. The way ARToolkit for Unity organises information is simple: • The mandatory component for ARToolkit is called a ARController. Aside from managing the camera parameters (for example, selecting the video input), it also records the complete list of markers your application will use, via ARMarker scripts (one per marker). • A "Scene Root" will contain everything you need to AR display. It is a standard (usually empty) object with a AR Origin script. the rest of the scene will be children of it. • The standard camera remains basically the same, but is now driven by a specific ARCamera script. By default, the camera is a video see-through (like a webcam). • Objects to be tracked are usually "empty" geomeries (GameObject--> Create empty) to which one attaches a special AR Tracked Object script.
    [Show full text]
  • Application of Augmented Reality and Robotic Technology in Broadcasting: a Survey
    Review Application of Augmented Reality and Robotic Technology in Broadcasting: A Survey Dingtian Yan * and Huosheng Hu School of Computer Science and Electronic Engineering, University of Essex, Wivenhoe Park, Colchester CO4 3SQ, UK; [email protected] * Correspondence: [email protected]; Tel.: +44-1206-874092 Received: 26 May 2017; Accepted: 7 August 2017; Published: 17 August 2017 Abstract: As an innovation technique, Augmented Reality (AR) has been gradually deployed in the broadcast, videography and cinematography industries. Virtual graphics generated by AR are dynamic and overlap on the surface of the environment so that the original appearance can be greatly enhanced in comparison with traditional broadcasting. In addition, AR enables broadcasters to interact with augmented virtual 3D models on a broadcasting scene in order to enhance the performance of broadcasting. Recently, advanced robotic technologies have been deployed in a camera shooting system to create a robotic cameraman so that the performance of AR broadcasting could be further improved, which is highlighted in the paper. Keyword: Augmented Reality (AR); AR broadcasting; AR display; AR tracking; Robotic Cameraman 1. Introduction Recently, there is an optimistic prospect on installing Augmented Reality (AR) contents in broadcasting, which is customizable, dynamic and interactive. AR aims at changing the appearance of a real environment by merging virtual contents with real-world objects. Through attaching virtual content on a real-world environment, broadcasting industries avoid physically changing the appearance of a broadcasting studio. In addition, broadcasters can tell a much more detailed and compelling story through interacting with 3D virtual models rather than with verbal descriptions only.
    [Show full text]
  • Calar: a C++ Engine for Augmented Reality Applications on Android Mobile Devices
    CalAR: A C++ Engine for Augmented Reality Applications on Android Mobile Devices Menghe Zhang, Karen Lucknavalai, Weichen Liu, J ¨urgen P. Schulze; University of California San Diego, La Jolla, CA, USA Abstract With the development of Apple’s ARKit and Google’s AR- Core, mobile augmented reality (AR) applications have become much more popular. For Android devices, ARCore provides ba- sic motion tracking and environmental understanding. However, with current software frameworks it can be difficult to create an AR application from the ground up. Our solution is CalAR, which is a lightweight, open-source software environment to develop AR applications for Android devices, while giving the programmer full control over the phone’s resources. With CalAR, the pro- grammer can create marker-less AR applications which run at 60 Figure 1: CalAR’s software structure and dependencies frames per second on Android smartphones. These applications can include more complex environment understanding, physical accessed through the smartphone’s touch screen. simulation, user interaction with virtual objects, and interaction This article describes each component of the software system between virtual objects and objects in the physical environment. we built, and summarizes our experiences with two demonstration With CalAR being based on CalVR, which is our multi-platform applications we created with CalAR. virtual reality software engine, it is possible to port CalVR ap- plications to an AR environment on Android phones with minimal Related Work effort. We demonstrate this with the example of a spatial visual- In the early days of augmented reality applications on smart ization application. phones, fiducial markers located in the physical environment were used to estimate the phone’s 3D pose with respect to the envi- Introduction ronment.
    [Show full text]
  • Augmented Reality and Its Aspects: a Case Study for Heating Systems
    Augmented Reality and its aspects: a case study for heating systems. Lucas Cavalcanti Viveiros Dissertation presented to the School of Technology and Management of Bragança to obtain a Master’s Degree in Information Systems. Under the double diploma course with the Federal Technological University of Paraná Work oriented by: Prof. Paulo Jorge Teixeira Matos Prof. Jorge Aikes Junior Bragança 2018-2019 ii Augmented Reality and its aspects: a case study for heating systems. Lucas Cavalcanti Viveiros Dissertation presented to the School of Technology and Management of Bragança to obtain a Master’s Degree in Information Systems. Under the double diploma course with the Federal Technological University of Paraná Work oriented by: Prof. Paulo Jorge Teixeira Matos Prof. Jorge Aikes Junior Bragança 2018-2019 iv Dedication I dedicate this work to my friends and my family, especially to my parents Tadeu José Viveiros and Vera Neide Cavalcanti, who have always supported me to continue my stud- ies, despite the physical distance has been a demand factor from the beginning of the studies by the change of state and country. v Acknowledgment First of all, I thank God for the opportunity. All the teachers who helped me throughout my journey. Especially, the mentors Paulo Matos and Jorge Aikes Junior, who not only provided the necessary support but also the opportunity to explore a recent area that is still under development. Moreover, the professors Paulo Leitão and Leonel Deusdado from CeDRI’s laboratory for allowing me to make use of the HoloLens device from Microsoft. vi Abstract Thanks to the advances of technology in various domains, and the mixing between real and virtual worlds.
    [Show full text]
  • Security and Privacy Approaches in Mixed Reality:A Literature Survey
    0 Security and Privacy Approaches in Mixed Reality: A Literature Survey JAYBIE A. DE GUZMAN, University of New South Wales and Data 61, CSIRO KANCHANA THILAKARATHNA, University of Sydney and Data 61, CSIRO ARUNA SENEVIRATNE, University of New South Wales and Data 61, CSIRO Mixed reality (MR) technology development is now gaining momentum due to advances in computer vision, sensor fusion, and realistic display technologies. With most of the research and development focused on delivering the promise of MR, there is only barely a few working on the privacy and security implications of this technology. is survey paper aims to put in to light these risks, and to look into the latest security and privacy work on MR. Specically, we list and review the dierent protection approaches that have been proposed to ensure user and data security and privacy in MR. We extend the scope to include work on related technologies such as augmented reality (AR), virtual reality (VR), and human-computer interaction (HCI) as crucial components, if not the origins, of MR, as well as numerous related work from the larger area of mobile devices, wearables, and Internet-of-ings (IoT). We highlight the lack of investigation, implementation, and evaluation of data protection approaches in MR. Further challenges and directions on MR security and privacy are also discussed. CCS Concepts: •Human-centered computing ! Mixed / augmented reality; •Security and privacy ! Privacy protections; Usability in security and privacy; •General and reference ! Surveys and overviews; Additional Key Words and Phrases: Mixed Reality, Augmented Reality, Privacy, Security 1 INTRODUCTION Mixed reality (MR) was used to pertain to the various devices – specically, displays – that encompass the reality-virtuality continuum as seen in Figure1(Milgram et al .
    [Show full text]
  • Calar: a C++ Engine for Augmented Reality Applications on Android Mobile Devices
    https://doi.org/10.2352/ISSN.2470-1173.2020.13.ERVR-364 © 2020, Society for Imaging Science and Technology CalAR: A C++ Engine for Augmented Reality Applications on Android Mobile Devices Menghe Zhang, Karen Lucknavalai, Weichen Liu, J ¨urgen P. Schulze; University of California San Diego, La Jolla, CA, USA Abstract With the development of Apple’s ARKit and Google’s AR- Core, mobile augmented reality (AR) applications have become much more popular. For Android devices, ARCore provides ba- sic motion tracking and environmental understanding. However, with current software frameworks it can be difficult to create an AR application from the ground up. Our solution is CalAR, which is a lightweight, open-source software environment to develop AR applications for Android devices, while giving the programmer full control over the phone’s resources. With CalAR, the pro- grammer can create marker-less AR applications which run at 60 Figure 1: CalAR’s software structure and dependencies frames per second on Android smartphones. These applications can include more complex environment understanding, physical accessed through the smartphone’s touch screen. simulation, user interaction with virtual objects, and interaction This article describes each component of the software system between virtual objects and objects in the physical environment. we built, and summarizes our experiences with two demonstration With CalAR being based on CalVR, which is our multi-platform applications we created with CalAR. virtual reality software engine, it is possible to port CalVR ap- plications to an AR environment on Android phones with minimal Related Work effort. We demonstrate this with the example of a spatial visual- In the early days of augmented reality applications on smart ization application.
    [Show full text]
  • Artoolkit 6/Open Source
    DAQRI ARToolKit 6/Open Source Introduction to ARToolKit Phil Oxford Brookes University 2017-01 DAQRI by the numbers DAQRI Smart Helmet Wearable Human-Machine Interface Hazloc-certified PPE helmet Sensor package: Logic board: • Intel R200 stereo colour/depth cameras Stereo holographic- Intel Core M7 CPU @ 2.1GHZ • Lepton 3.0 Thermal Camera waveguide full colour 8GB RAM • DAQRI VisionCube™ integrated see-through display Wireless radio IMU/wide FOV optical tracking system DAQRI’s approach to AR The DAQRI Ecosystem 4D Studio Services Analytics MDM, Remote Expert Operating System Software Core apps Advanced computer vision External framework plugins } Hardware Smart Helmet, In-vehicle display Physics Realtime holographics ARToolKit: A collection of software tools to help solve some of the fundamental problems in augmented reality, including geometric and photometric registration • geometric registration: aligning the position of the virtual environment with the actual • photometric registration: matching the appearance of objects in the virtual environment to the actual ARToolKit - History • 2004 - v.2 released open source (Sourceforge) • 1999 - first demonstrated publicly • 2008/2012 - open source innovation • 2001- v.1 released open source (Washington) • 2012/2014 - extending platform support • 2001 - ARToolworks incorporated with dual licensing model • 2015 - acquired by DAQRI - pro versions open sourced 1999 2009 2015 SIGGRAPH 1999 ARToolKit Shared Space demo VR2009: Kato award ARToolworks becomes part of DAQRI (Lamb, Vaughan, Furness, Billinghurst, Kato) 6 Goals • Open-source a high-quality texture-tracker. • Modernise target platforms and reduce need for legacy support. • Create SDK suitable for full spectrum of expertise • high-level low-complexity API for novices • expose underlying CV APIs for experts while simplifying ancillary tasks ARToolKit 6: Computer vision ⁕ On-device image recogniser ⁕ Multiple textured-surface tracker ⁕ Planar surface tracker .
    [Show full text]
  • Flightsim Community Survey 2019
    FlightSim Community Survey 2019 Final Report 1 Copyright Notice © 2020 Navigraph By licensing our work with the CC BY-SA 4.0 license it means that you are more than welcome to copy, remix, transform and build upon the results of this survey and then redistribute it to whomever you want in any way. You only have to give credit back to Navigraph and keep the same license. https://creativecommons.org/licenses/by-sa/4.0/ 2 Preamble This is the annual flightsim community survey, a collaborative effort between partners – developers, companies and organizations in the flightsim domain – coordinated and compiled by Navigraph. This survey is freely distributed for the common good of the flightsim community to guide future projects and attract new pilots. This flightsim community survey is the largest and most comprehensive of its kind. This year 17,800 respondents participated in the survey. This is an 18.6% increase from last year when 15,000 participated. This year’s survey consisted of 93 questions, compared to last year’s 77 questions. However, this year many more of the questions were conditional, allowing us to add new sections and ask in-depth questions only to those respondents for whom it was relevant. New sections this year contained questions specifically aimed at pilots using flight simulator software on mobile devices and helicopter flight simulators. We also added questions on combat simulators, air traffic control and flight planning. Finally, because of the upcoming release of the new Microsoft Flight Simulator 2020, we added questions on this topic as well. Our main objective this year was to recruit more and diverse partners to broaden the reach of the survey to get an even more representative sample of the community.
    [Show full text]
  • Freetrack Manual
    FREETRACK MANUAL June 2007 by Babasior. With the participation of The_target. English Translation by Gweeds. Manual Version 1.2. 1. Introduction 2. Materials and Equipment necessary to the operation of FreeTrack 3. Head gear Construction 4. Installation of FreeTrack 5. Setting up and tweaking FreeTrack 6. FreeTrack.ini 7. Mouse Emulation 8. Joystick Emulation 9. Keyboard Emulation 10.Profile Creation 11.List of Games and their possible movements Note: TrackIR is a registered trademark of Natural Point Inc. Windows XP and Windows Vista are trademarks of Microsoft Corporation. 1. Introduction: FreeTrack is software which simulates movements of your head within a game hence increasing realism and the pleasure of game play. To achieve this, FreeTrack uses a standard Webcam and head mounted markers which consist of four Infrared LED (light emitting diodes) mounted on a standard baseball cap. FreeTrack uses the Webcam to “see” the LED's and so it can calculate the position and movement of your head and feed this information to your game. FreeTrack functions in the same way TrackIR does and is compatible with the majority of games using head tracking technology. The latest version of FreeTrack is available at this address: http://n.camil.chez-alice.fr/index.php Or on the site of Didja at this address: http://freetrack.online.fr/ 2. Materials and Equipment necessary to the operation of FreeTrack: – a PC running Microsoft Windows XP SP2 or Windows VISTA – DirectX 9.0c installed – Processor with SE instruction set – Webcam – 4 diodes IR (ref. OSRAM SFH485P or equivalent), failing this, 4 bright red or orange diffused LED's can be used.
    [Show full text]