šŸŽ‰We can now proudly present the winners of the TAPAS Community Challenge 2018! šŸŽ‰
Congratulations to Team "Wireless Charging" (idea 56). We are really excited for all finalists and a really big thank you to all participants for your interest in this challenge!

We got over 200 submissions! 65 ideas got one or more TAPAS boards, 10 submissions were presentation-ready.
And now we have 5 finalists! YEAH šŸ˜ƒ The finalist's idea numbers were 40, 56, 68, 212 and 213.
What's next?
We are now preparing the next steps for you, the community. Please stay tuned!
We are working on a forum and a separate webpage. If you have any question please don't hesitate to contact us via email!

Open-Source Software-Defined Magneto-Optical Modulator

Since the submission deadline has come, all further development will happen publicly on this GitLab page:




The goal of this project is to produce a device, which will be able to modulate the polarization of light, such as a laser beam, with a software-defined waveform.


Why is this useful?

This device will provide a powerful and versatile tool to perform a broad spectrum of measurements (e.g. polarimetry, ellipsometry, etc.) with with much higher precision compared to conventional methods. This enhancement of precision can be achieved, when combining the optical modulator with phase- and frequency-sensitive detectors, such as lock-in amplifiers, which can extract the relevant information even from extremely noisy measurement data.

Who would benefit from it?

Since this design will be Open-Source Hardware and Free Software, researchers of various disciplines (e.g. optics, chemistry, biology, etc.) in laboratories all over the world, especially where the research budgets are small, can benefit from this project. Since it can serve as a low-budget solution, laboratories, that do have the people to build things, but not the budget to buy expensive equipment, will get access to this technology.

Furthermore, the nature of Open-Source Hardware enables students, researchers, professionals or makers to innovate on top of this project, and develop customized versions and derivatives, specially adapted to a specific need.

Technical Setup

A Wi-Fi connected single-board computer, such as the Raspberry Pi, serves a browser-based graphical user interface for the web app that controls a stack of two TAPAS SDIs, whereas each TAPAS SDIs provides a synchronized software-defined current waveform, which will be fed into two solenoid electromagnet coils, as shown in FigureĀ 1. A crystal with large Verdet constant, such as terbium gallium garnet, is placed in the cores of the solenoid to provide the optical modulation, which corresponds to the current waveform as defined by the user within the GUI.

As a simple example application, the solenoid with the crystal inside is placed inside the optical path of a polarimeter setup, as shown in Figure 2.

However, for the full measurement of the polarization of an unknown light source, such as the light of a star or the light emitted during a physical or chemical process, two solenoids with crystals with 45Ā° rotation with respect to each other are placed before a linear polarizer with polarization direction of 22.5Ā° the crystal is placed inside the optical path of a polarimeter setup, as shown in Figure 3.


  • Chivintar Amenty
    Undergraduate student
    University of Crete, Physics Department

  • George Katsoprinakis, PhD
    Post-Doctoral Researcher
    Foundation for Research and Technology ā€“ Hellas, Institute of Electronic Structure and Laser

  • Dimitris Koukoulakis, Mres
    Research Director - Software Engineering
    CommonsLab Makerspace

  • Jann Kruse, PhD
    Research Director - Embedded Systems
    CommonsLab Makerspace
  • Jann Eike KRUSE
  • May 2 2018
  • Jul 6, 2018

    Admin Response

    This idea submission is among the finalists and will be presented at the CKI Conference in Erlangen.

  • Admin
    Nora Schille (TAPAS team) commented
    May 03, 2018 12:01

    Hi Jann,
    thanks for your submission. What a nice idea.
    We want to provide you and your team a TAPAS board. One of my colleagues will message you shortly.

    Nora @ TAPAS team

  • Jann Eike KRUSE commented
    May 25, 2018 15:59

    Hi Nora,

    Thanks for the feedback and for the TAPAS board, which arrived the last week at our lab and which we have already started working on.

    Anyhow, taking a closer look at the board, I realized, that the voltage outputs (P1_OUT, P2_OUT and P3_OUT) are only positive polarity, i.e. 0-48V. For our application we need to switch the direction of the current, so we need to connect the solenoid between two outputs (between P1_OUT and P2_OUT, where one will act as source and the other will act as current sink) rather than just between one output and ground.

    This means that we can connect only one solenoid per TAPAS board, and not three solenoids on one board as I assumed by mistake.

    In order to make a proper polarization measurement (full set of stokes parameters) of a given light source, we need two optical modulators, i.e. two solenoids, i.e. two TAPAS boards.

    Is it possible to send us a second TAPAS board?
    Then we could build and demonstrate a complete stokes polarimeter!
    (I updated also the project description accordingly.)

    Thank you very much and best greetings,

  • Susanne Forster commented
    May 29, 2018 08:51

    Hey Jann,

    we will provide you another board.

    A colleague will contact you shortly.

    Best regards,

    Susanne @ TAPAS team

  • Admin
    Nora Schille (TAPAS team) commented
    June 04, 2018 13:56

    Hi Jann,

    I hope the boards is arriving shortly. It was sent to you last week.
    How is it going? Do you need any help regarding the realization of your project?
    Here is just a friendly reminder that submission deadline for your presentation is on 24th of June. :-)Ā We are really excited to see your progress!Ā 
    Please post the progress within your idea board submission.

    PS: We want to do a community call with you! Please useĀ our doodle to find a date which fits best for you.Ā :-)

    Nora @ TAPAS Team

  • Jann Eike KRUSE commented
    June 12, 2018 09:45

    Thanks for the second TAPAS board!

    As you can see in the attached image, we have 3D-Printed the bottom part of the "Tapas_housing_bottom.stl" as well as some simple spacers, in order to put the two TAPAS boards and the Raspberry Pi Zero W on top of one another with stackable headers.

    We are now in the progress of winding and testing the solenoid coils. We are also going to program the C2000 Piccolo LaunchPad (LAUNCHXL-F28069M), which has the same MCU on board (TMS320F28069). So it is roughly compatible with the TAPAS for the purposes of getting started easily with the Code Copmoser Studio. And later we'll program the two TAPAS through their JTAG ports.

  • Admin
    Nora Schille (TAPAS team) commented
    June 14, 2018 08:28

    Hey Jann,
    thank you for the feedback! Nice to hear that you get along with the things :)
    Keep doing great!

  • Jacqueline Hofmann commented
    June 20, 2018 12:37

    Hey Jann,

    Please keep in mind that the submission deadline for your presentation is on 24th of June! We are already looking forward to seeing how you brought the TAPAS board to life! :-) Remember that you still have time to work on the implementation of your idea after the submission!

    Please upload your presentation and everything you want to share with us in your idea board entry.

    Good luck :-)

    Jacqueline @ TAPAS Team

  • Jann Eike KRUSE commented
    June 24, 2018 20:40

    The C2000 Piccolo LaunchPad (LAUNCHXL-F28069M) arrived at our lab. We use it for software development, since it has the same chip as the TAPAS. Using the Energia IDE, we ran a simple "blink" example program to toggle two GPIOs which connect to two on-board LEDs on the LaunchPad. (See video.) The simple blink is a first step towards toggling the GAN FETs of the TAPAS' power stage, and thus changing the polarity of the current flowing through the coils and consequently the direction of the magnetic field in the solenoid.

  • Jann Eike KRUSE commented
    June 24, 2018 20:55

    After a few different approaches and tests, the free-standing test coil with length L=30mm, inner diameter ID=15mm and 347 turns of āŒ€1.2mm (~16AWG) wire has measured the expected 0.1 Tesla at 14 Ampere at the center of he coil. (See attached photo.) The total voltage drop was 8.6V, which results in 120 Watt of ohmic loss. This can be slightly improved towards about 95 Watt by using 1.6mm (~14AWG) wire and a few more turns. Anyhow, we will go for water cooling.

  • Jann Eike KRUSE commented
    June 25, 2018 12:05

    Our time-line for the next weeks:

  • Susanne Forster (TAPAS team) commented
    June 26, 2018 12:58

    Hey Jann,

    we really like your idea.

    It would be great if you could share a video of your project with us!


    Best regards,

    Susanne @TAPAS team

  • Jann Eike KRUSE commented
    June 26, 2018 15:40

    Ā Hi Susanne,

    Sure, I'll try upload a video clip tomorrow.


  • Jann Eike KRUSE commented
    June 28, 2018 10:07

    You can find a video showing our progress on YouTube:


  • Andreas Rom commented
    June 28, 2018 13:44

    Hi Jann -

    First of all I want to tell you, that I really like your approach starting programming with the C2000 Piccolo LaunchPad (LAUNCHXL-F28069M);
    I guess that this is the best thing you could do for software-development to make sure, that your TAPAS-board will stay healthy during implementing everything especially related to pwm....checking your produced waveform e.g. with an oscilloscopeĀ beforeĀ using the firmware with the TAPAS isĀ definitely necessary toĀ make sure your TAPAS stays okay during development phase. I wouldĀ recommend this way of development to everybody who isĀ working with TAPAS. Ā 

    We are all very interested in the outcome of your project!

    When you start going to the TAPAS-board, please make sure to use a high PWM-frequency ( >= 120kHz)Ā because of the filters that are onboard of TAPAS and also ensure using a proper deadtime (at least 10ns)Ā setting for the halfbridges.

    Those two points will be mandatory for your TAPAS board to survive

    Andreas @ TAPAS team

  • Jann Eike KRUSE commented
    July 16, 2018 11:35

    Hi Andreas,

    Thanks for you feedback and your hints regarding PWM and dead times!
    I'm still in the progress of getting to grips with the Code Composer Studio and the PWM / ePWM / HRPWM counter/timer settings and registers of the MCU. But I'll make sure to keep the necessary dead-times and to stay above 120kHz with the output frequency and test it on the LaunchPad before I upload any code to the TAPAS. Anyhow, I'm starting with some +/- DC tests (full HIGH, full LOW). Then I'll go for some PWM "steady-state" (constant duty cycle) tests. Later I'd like to implement PWM with current-feedback and finally I want to have arbitrary AC/DC current waveforms. So software-wise we still have a bit of a walk ahead of us.

    The hardware on the other hand has successfully passed the first tests last Friday, with just a green laser pointer a small TGG that we "borrowed" from an optical isolator. The results showed us that, even with this basic setup, we can easily achieve 30Ā° (peak-to-peak) optical rotation. Now we just need to attach the water cooling system, so we can run higher currents and achieve stronger magnetic fields and larger optical rotations. Then we box it properly and wait for the delivery of the larger TGG crystal.
    [See attached photo.]


  • Jann Eike KRUSE commented
    July 17, 2018 13:11

    Today we received all the parts for our water cooling system. [See attached image.] So now we can test the temperature response of the coil at different currents and magnetic fields.

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