Open Hardware and Free Software: Teufel Mynd, a case study
The FSFE's volunteer and open hardware passionate, Nicole Faeber
read about the Teufel Mynd speaker announced as an "Open Source Project", so
she decided to put it to the test. We, the FSFE, bought
one and she dug in. Curious what she found? Read along with us!
Teufel Mynd Bluetooth speaker box
Open hardware and Free Software are about more than tinkering:
they give users the freedom to inspect, modify, and truly understand the
technology they rely on every day. Open hardware means the design of a
device is publicly available: anyone can study how it's built, improve
it, or manufacture it themselves. Free Software goes hand in hand with
this: it guarantees that the code running on your devices can be use,
study, share, and improve by anyone. Together, they ensure that whoever
owns a device gets to decide what runs on it, free from manufacturer lock-in or
hidden restrictions.
This article has not been sponsored by Teufel
in any way. We bought the device to test from our own money and
did all research on our own.
In May 2025 the German audio hardware maker company Teufel
announced a new product, the Mynd Bluetooth speaker box. The
speaker in itself is yet another Bluetooth speaker box, the remarkable
feature of it is that it was announced as an "Open Source Project" with
"high repairability and sustainability", with all mechanical and
electronics design files as well as the firmware source code published
as "open source". So they mean the Mynd to be a Free Software and open
hardware product.
So we wanted to put this to a test!
TL;DR - A Quick Summary
The Teufel Mynd project is a pretty impressive example of an Open
Source Hardware project. All the mechanical and electronics design files
are made public under a permissive license granting the four freedoms -
to study, to share, to modify and to distribute modified versions of it.
The data is complete enough to recreate the whole hardware, the
mechanical enclosure as well as the electronics PCBs.
There are only two caveats:
- The loudspeakers themselves are, at least very likely, Teufel
proprietary and Teufel does not sell them as spare parts.
- The firmware for the Bluetooth module along with some DSP and USB
type-C controller firmware are not Free Software. But at least the files
are provided as binary blobs so one can build a complete firmware update
file.
So the project fulfills the Open Source Hardware Definition.
Let's dive into the details!
Repairability
Many current consumer electronic devices these days are not repair
friendly. Cost pressure and ease of mass production make the
non-repairable options, like glue instead of screws, very appealing to
manufacturers.
The Mynd is very different in this regard. The case is held together
by screws, not glue. The parts are pieced together tightly with proper
rubber seals, not glue strips. The screws are clearly visible and
marked, not hidden away under some sticker label or warranty seal. The
different screw sizes and types are documented on the bottom of device
itself. Also the starting point to pry the casing parts apart after
taking out the screws is marked on the case. So opening the device is
really made as easy as possible, no guessing, the steps for dis- and
reassembly are clear and pretty much self explanatory.
Mynd opened
There is just one caveat, availability of spare parts. So far Teufel
only offers the battery pack and carrying belts as spare parts, not the
Printed Circuit Boards (PCBs) or speaker chassis themselves. Maybe it is
possible to convince the Teufel service center to buy these, but
Teufel's general policy for spare parts says: "Please note: We do not
ship circuit diagrams, toner, or electronic components such as circuit
boards, capacitors, and resistors". For the average customer, this limits repairability.
Open Hardware
As promised in the product announcement, Teufel made all hardware
design files publicly available on GitHub. All these files are,
where applicable, licensed under the Creative Commons
"Attribution-ShareAlike 4.0 International" license which allows the four
freedoms: Use, study and modify, redistribute the original and
modifications.
This is pretty remarkable!
3D CAD, the casing
All components of the case are split into separate 3D CAD files and
are available in 3DM, STL and STP format. In total there are 11
different parts that make up the case / chassis. Here we have the main
case STP file opened in FreeCAD:
Teufel Mynd speaker opened and dismantled
So yes, everything is there, the full case and all its parts! Can you
remake it, like 3D print? Well, let's see, here is the front grill STL
file opened in the Cura 3D printer slicer:
This is looking pretty good! Since the Mynd speaker box is quite big
you of course need a large 3D print room, the front grill is 26cmx18cm.
But the problem is in the details. The 3D CAD design has not been
optimised for 3D printing but rather for injection mold production so
this makes 3D printing difficult and we can see the issue when looking
at the print plate from underneath:
All the red parts are free floating, i.e. these do not touch the
print surface and will create issues while printing. With some luck and
a good printer these will still come out OK but they may also end up
quite ugly. Another a bit problematic part are the "knobs" on the top
side which hold the front grill tight in rubber gaskets of the speaker
fixture:
These little knobs also have some overhangs which can create issues
while printing.
So is the CAD design indeed "open hardware"? Yes! It is open licensed
and you can use Free Software tools like FreeCAD or Cura slicer to
tinker with it, even try to reproduce parts e.g. using 3D printing. The
3D printing limitations (overhangs etc.) are not a detriment to the open
hardware nature, nothing requires open hardware to be easily
reproducible.
Electronics, schematics and PCBs
Next let's have a look at the electronics design, also for this all
relevant files are available in the same hardware GitHub repository
under the same "Attribution-ShareAlike 4.0 International" license. Again
the files are made available in three file formats: Altium Designer,
KiCAD and PDF. The PDF files are PDF exports of the schematics and the
printed circuit board (PCB) layout. The Altium Designer and KiCAD
formats are the much more interesting ones since these contain the
editable schematics and PCB layout! Since we only use Free Software we
cannot use the Altium files, so we focus on the KiCAD version for now -
I assume that the original design was made using Altium and was then
exported to KiCAD.
Excursion: Electronics making
To design and finally make a piece of electronics, a number of pieces
are needed. First you need to have some idea what you are going to make,
of course. Based on this you need to start choosing components for your
design - which chips to use, which power supply these need, how this
needs to be designed with which parts etc. So from a very early stage
the component selection is a critical first step, we'll also come back
to this a little later.
Next you need to start to draft your electronics design, i.e. how all
the components are connected to each other. This is done in the so
called schematics. Every single connection of each of the components is
made here. The schematics usually does not look similar to the final
PCB, it is a rather abstracted view on the hardware and focuses on the
parts choice and the connection between the parts.
Once the schematics is somewhat ready the next phase is a real time
sink, creating a PCB layout from the schematics. Tools like Altium or
KiCAD assist with it, they know the physical sizes and constraints of
the components and visualize it for you. But in the end the engineer has
to properly place them on the virtual PCB. Placing is not only a matter
of just putting them somewhere but you also need to know electrical
constraints and keep routing the connections in mind. Creating a PCB
from known schematics can take days and weeks and needs a lot of
experience. Adding to that there may be mechanical constraints as well,
e.g. known maximum PCB sizes or shapes that need to be taken into
account.
Once the schematics and PCB layout is done the PCB can be ordered
from a PCB manufacturer and all electronic components can be ordered
from the various distributors. In many cases you need to order from more
than one distributor because not even the large ones carry all
components - and fingers crossed everything is in stock!
Once PCBs arrive and all parts are at hand you can finally start to
assemble the PCB and power it up for the first time: Good luck the
"magic smoke" stays within the parts!
The main board
So let's have a look at the main PCB as an example:
The Teufel engineers created a full KiCAD project for each PCB that
can be directly and completely opened in KiCAD with all parts -
schematics, footprints, 3D components and the full PCB design. Here is
one page of the main PCB schematics for the main microcontroller:
Schematics
The schematics only show a limited level of detail, some details
necessary for actually making a device are not shown. For example the
component with designator "C22C" right of the microcontroller unit
(MCU), in the schematics you can only see that it is a capacitor with
100nF capacity. But the actual specification needed contains a lot more
information, which is also contained in the KiCAD project:
Example component C2C
So here you can see that it is rated for maximum voltage of 50V, has
a temperature coefficient of X7R, a tolerance of +/-10% and that the
physical so called "footprint" is 0603, which means a surface mount
device (SMD) 6mil long and 3mil wide - 'mil' is 100th of an inch, a
common size in PCB design, so about 1.6mm in length and 0.8mm wide. A
pretty small component. Each and every component needs to be specified
this way.
For a capacitor one usually can find components with the same
specification from different manufacturers which makes component
sourcing a bit easier. Some distributors allow importing a Bill Of
Material (BOM) into their shop system and will offer best matches. For
some other components there can be a variety of choices with very
similar specifications which can make picking the right one complicated.
In this case an exact manufacturer part number comes to the rescue:
Example MCU
In this example there is the main PCBs microntroller unit, specified
with its exact manufacturer and the manufacturer's part number, ready
for ordering.
Speaking of ordering, it is also quite common, especially for
commercial projects, to also specify an ordering source within the
project, so that later on a BOM can be exported and handed over to e.g.
a purchasing person or department for ordering all the components. In
the KiCAD Mynd project there are no ordering sources.
So, are the electronics design schematics open hardware? Yes! It is
licensed under an open license providing the four freedoms. All
necessary information to understand the schematics is included as well
as all information to make a PCB from the schematics.
PCB layout
And now to the real fun part, the PCB layout. I won't go into the
details here because there would be too much to cover. Just to give an
idea here is the main PCB view in KiCAD's PCB editor:
Main PCB layout, KiCAD
This is a 4-layer PCB, i.e. it has four layers of copper traces, top,
bottom and two in between. This PCB alone carries 561 components! Many
of them small SMD components, the smallest being some 0402 resistors
(4mil x 2mil = ~1mm x ~0.5mm). And to make things even worse, there are
components placed on both sides of the PCB which makes soldering even
more complicated. In KiCAD there is an awesome feature to create an
interactive 3D view of the designed PCB, here is the Mynd Main PCB front
and back:
KiCAD 3D Mynd PCB front
KiCAD 3D Mynd PCB back
In total there are nine (9) PCBs in the Mynd speaker box, the main
and amplifier PCBs being the largest and most complex. In total there
are 1047 components on these 9 PCBs, about 87 different types of
components. Just managing the supply and stock of 87 different component
types is, I can tell from experience, a major effort.
Is the PCB layout open hardware? Yes! You have the four freedoms and
the hardware design details are complete enough to rebuild the whole
thing! From parts specification to PCB specification (so called "stack
up") everything is there. The only issue one might run into trouble with
is finding ordering sources for all the components, but that's probably
outside of the scope of open hardware anyway.
Make it yourself?
Well, I have not tried, but looking at the design files, mechanical
and electronics, I think building the Mynd speaker hardware from scratch
should be possible. I have not found any information missing, except
maybe ordering sources for the components. Placing and soldering all
over 1000 components on the nine PCBs will be a major effort and with
components down to 0402 will be difficult to place by hand, some pick
& place setup would be very helpful along with proper SMD reflow
soldering equipment. But the important part here is that there is no
information missing in the design files, it's all there.
3D printing the case could be possible as well, with some additional
effort to accommodate for 3D printing instead of injection molding. The
result will very likely look and feel differently, but it could
work.
What will definitely become a problem are the Teufel specific custom
parts, i.e. the speaker chassis themselves. Other parts like the rubber
gaskets and rubber seals these are also in the 3D design files but will
be hard to e.g. 3D print properly.
The firmware
And now to the final part, there is also some software involved! The
main MCU, a STM32 microcontroller, runs some software as well as is the
module used for the Bluetooth connectivity and sound generation. The source
code and build scripts were also made available by Teufel. The parts
created by Teufel, i.e. the application software running on that STM32
MCU, are licensed under the MIT license. But for building it, some more
dependencies are needed, like some software development kit (SDK) bits
from ST-Micro (Apache 2.0, BSD 3-clause, MIT, proprietary ST SLA), bits
and pieces of FreeRTOS (MIT) and some more proprietary binary only
parts for the Bluetooth module, the audio DSP and, last but not least,
the USB type-C port controller - yes, also these things have their own
firmware these days.
So apart from the blobs everything is Free Software, which is pretty
cool! The blobs though are a bit of a bummer. But is this Teufel's
fault? Or does this make the whole project less "open hardware"?
My personal take on such blobs is this: While I dislike proprietary
blobs in general, because they limit our freedoms to use the hardware as
we like, I can at least accept certain blobs, e.g. in the case where
chip+blob form a kind of union so that I can basically view the two
together as just a single piece of hardware. I still don't like it,
because it is hidden software, but at least I can somewhat accept it. We
have this kind of situation in many cases and are somewhat OK with it -
the WiFi firmware in our WiFi cards, the firmware in the touchpad
controller of our laptops etc. The list is long, very long. How to
properly address and fix this is another story we need to come back to
another time.
The firmware package can be built using the free GNU GCC cross
compiler for ARM and build the firmware for the STM32 MCU. The firmware
blobs for the DSP, Bluetooth module and the USB type-C controller do not
get built and it is also not documented how to program these. But at
least the binaries are there.
So is the firmware Free Software? Concerning the MCU firmware, yes,
it is. All firmware? No, there are certain blobs.
Especially sad is that the Bluetooth part is completely binary only
in the Bluetooth firmware blob, so all pairing, Bluetooth audio protocol
(A2DP with SBC) etc. is hidden in that blob and can not be changed - I
would have been curious if SBC-XQ (higher quality audio codec) or TWS
(True Wireless Stereo) could be added to that Bluetooth firmware.
Final verdict
So, is it open hardware?
Mechanical design / parts: Yes! Everything is documented properly,
some special components are not available off the shelf and need
alternative sources, especially the speakers. It would be great if
Teufel would also supply these through their spare parts shop.
Electronics design: Yes! The KiCAD files contain everything one needs
to completely recreate and especially repair the electronics. Some
components may be difficult to source though (like the Bluetooth
module).
Firmware: The Teufel made parts are Free Software, some third party
firmware parts are not (USB type-C controller, DSP, Bluetooth
module).
With all that it also qualifies nicely for the Open Source Hardware
Definition by the Open Source Hardware Association (OSHWA).
Overall I think the Teufel engineers did an extremely good job here!
They definitely set the bar and have given a great example of how one
can make open and sustainable consumer hardware. For some first hand
insights there is a nice interview
with the engineers published on the
Prototype Fund website (in German).
Will the openness detriment their business? I am fairly sure it
won't. Yes, maybe competitors can learn a bit about high quality
engineering, but on the other hand this isn't rocket science either.
Will they loose business because people will now rather build it
themselves instead of buying a ready made device from Teufel? I doubt
that. While I am quite convinced that one could build a complete Mynd
device from the open specifications, it would take many many work hours
- the logistics for the over 1000 electronic components, populating the
PCBs, 3D printing or otherwise making the enclosure etc. - this is a
serious undertaking and will take weeks along with dozens of person
hours. A good hacking experience, for sure! But economically definitely
not worth it, better go and support the company that made it with a
purchase.
Outlook
Open Hardware not only means better repairability and with it better
sustainability. It also means possible enhancements too! For example the
Bluetooth module in the factory Mynd only supports the rather mediocre
SBC audio codec. But since the electronics are made modular and the rest
of the system is documented so well, why not think about replacing this
limiting Bluetooth module by something else? By something more
capable?
Why not replace it with an ESP32 based module plus high quality audio
codec chip? Would not be the first ESP32 based audio device.
Why stop at an ESP32? There is a
discussion going on in the GitHub
Mynd hardware repository about replacing the proprietary Bluetooth
module with a Raspberry Pi Zero 2 W based module! This would not only
enable other Bluetooth audio codecs but then you would also get a
complete Linux system into your Mynd, with its own media playback
capabilities! Prototypes already seem to exist.
This is the brilliance of Free Software and open hardware, the limit
is your imagination, it is in your hands.
Happy hacking!
Do you care about sustainability, repairability and Free Software?
Did you do research about which products work best with Free Software?
Have you ever tried to tinker with them? We would love to hear your
experiences. Please, share your knowledge with us. We want to know
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devices! Moreover, if you are a skilled Free Software enthusiasts
who would like to volunteer to also analyse devices, please get in touch with us, so we can work
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