--- /dev/null
+#+TITLE: Portable stereo speaker
+#+AUTHOR: Svjatoslav Agejenko
+#+LANGUAGE: en
+
+* (document settings) :noexport:
+** use dark style for TWBS-HTML exporter
+#+HTML_HEAD: <link href="https://bootswatch.com/3/darkly/bootstrap.min.css" rel="stylesheet">
+#+HTML_HEAD: <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.min.js"></script>
+#+HTML_HEAD: <script src="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.5/js/bootstrap.min.js"></script>
+#+HTML_HEAD: <style type="text/css">
+#+HTML_HEAD: footer {background-color: #111 !important;}
+#+HTML_HEAD: pre {background-color: #111; color: #ccc;}
+#+HTML_HEAD: </style>
+
+* General
++ DISCLAIMER: I DO ELECTRONICS AND 3D DESIGN SOLELY AS A HOBBY. THERE
+ COULD BE ERRORS THAT CAN RESULT IN ALL KINDS OF DAMAGE. USE THESE
+ DESIGNS AT YOUR OWN RISK.
+
++ This design is released under Creative Commons Zero (CC0) license.
+
++ Author:
+ - Svjatoslav Agejenko
+ - Homepage: https://svjatoslav.eu
+ - Email: [[mailto://svjatoslav@svjatoslav.eu][svjatoslav@svjatoslav.eu]]
+
++ See also:
+ - [[../../index.html][Other physical projects in this repository]]
+ - [[https://www.svjatoslav.eu/projects/][Other projects hosted at svjatoslav.eu]]
+
+* Project description
+I had pair of good compact stereo speakers lying uselessly around as
+well as secondhand TDA2030 Chinese knockoff audio amplifier chips.
+Also I wanted to test modular construction approach: motherboard with
+shared bus and functionality realized via pluggable modules. So I
+built stereo speaker:
+
+[[file:make.png]]
+
+Indicator on the front panel shows available power within the
+system. Ideally it should be at the maximum. It drops when batteries
+run empty or when consumed power (too loud music) is greater than
+onboard power supply or batteries can handle. It has on/off switch and
+stereo audio input. Audio input impedance is about 100 ohms.
+
+[[file:make,%20side.png]]
+
+Idea for the holes on the top and smaller ones on the bottom back is
+to enable air flow for passive cooling.
+
+[[file:make,%20back.png]]
+
+Entire construction is made of parts, no larger than
+120x120x120mm. Maximum for my printer.
+
+* Battery holder
+Device is powered by 4 times AA NiMH batteries (1.2V each).
+
+[[file:battery%20holder/schematic.png]]
+
+I happened to have AA battery adapters lying around with different
+bottom hole configurations. Therefore this weird hole design:
+
+[[file:battery%20holder/battery%20holder.png]]
+
+Download:
++ [[file:battery%20holder/battery%20holder.FCStd][FreeCAD file]]
++ [[file:battery%20holder/battery%20holder.stl][STL file]]
+
+Result:
+[[file:battery%20holder/make.png]]
+
+Attaches to the back of the body:
+[[file:battery%20holder/mounted%20on%20the%20back.png]]
+
+* 20V up-step module
+Battery pack voltage is routed through main on/off switch on the front
+panel, and then it goes to the 20V up-step module.
+
+[[file:20V%20upstep%20module/schematic.png]]
+
+It uses ready made upstep module, but adds extra voltage filtering via
+inductor and capacitors.
+
+[[file:20V%20upstep%20module/make.png]]
+
+* Main board
+
+Voltage upstep above sits on top of main board (motherboard). It has
+uniform central bus that spans all connectors.
+
+[[file:main%20board/internal%20bus.png]]
+
+[[file:main%20board/bus%20on%20the%20bottom,%202.png]]
+
+First row of the main board is special IO terminal (for connecting
+speakers, front panel, etc..)
+
+[[file:main%20board/IO%20terminal.png]]
+
+Remaining rows are for connecting boards:
+
+[[file:main%20board/1.png]]
+
+To provide structural support, main board is attached to frame:
+
+[[file:main%20board/board%20fixator%20body.png]]
+
+Download:
++ [[file:main%20board/board%20fixator%20body.FCStd][FreeCAD file]]
++ [[file:main%20board/board%20fixator%20body.stl][STL file]]
+
+And boards plugged into main board are fixed at the top, using clip:
+
+[[file:main%20board/board%20fixator%20top%20clip.png]]
+
+Download:
++ [[file:main%20board/board%20fixator%20top%20clip.FCStd][FreeCAD file]]
++ [[file:main%20board/board%20fixator%20top%20clip.stl][STL file]]
+
+Result:
+
+[[file:main%20board/bus%20on%20the%20bottom,%201.png]]
+
+[[file:main%20board/board%20fixator.png]]
+
+* Mono audio amplifier module
+
+Design uses scavenged secondhand Chinese TDA2030 audio amp
+clones. Each chip is mono audio amplifier. Therefore 2 almost
+identical audio amp modules had to be built, one for left speaker, one
+for right.
+
+[[file:mono%20audio%20amp%20module/schematic.png]]
+
+I like to build on top of prototype PCBs. Gives results much faster
+for one-off projects. Before soldering, I solve component layout on
+paper:
+
+[[file:mono%20audio%20amp%20module/PCB%20layout.png]]
+
+Result - front:
+
+[[file:mono%20audio%20amp%20module/assembled%20front.png]]
+
+Result - back:
+
+[[file:mono%20audio%20amp%20module/assembled%20back.png]]
+
+Here copper tape is used as improvised heatsink.
+
+* Speakers
+
+High frequency small speaker and medium frequency bigger speaker are
+combined.
+
+[[file:speakers/schematic.png]]
+
+Capacitor acts as high-pass filter on top of tiny PCB:
+
+[[file:speakers/PCB%20layout.png]]
+
+Speaker enclosure:
+
+[[file:speakers/speaker%20enclosure.png]]
+
+Download:
++ [[file:speakers/speaker%20enclosure.FCStd][FreeCAD file]]
++ [[file:speakers/speaker%20enclosure.stl][STL file]]
+
+Speaker enclosure cover:
+
+[[file:speakers/speaker%20enclosure%20cover.png]]
+
+Download:
++ [[file:speakers/speaker%20enclosure%20cover.FCStd][FreeCAD file]]
++ [[file:speakers/speaker%20enclosure%20cover.stl][STL file]]
+
+Result:
+
+[[file:speakers/make.png]]
+
+* Front panel
+
+Initial idea was really simple panel:
++ on/off switch
++ system power indicator
++ stereo audio input
+
+But, since I'm using "agile" approach, during load-testing, it become
+clear that active fan based cooling would be nice (when playing loud
+music). I found tiny cooler fan that needs 5 volts to operate. Also I
+need to power backlight for power indicator. For both of these cases,
+I decided to add another voltage up-step module (target voltage output
+set to 6V). This time directly on the front panel.
+
+[[file:front%20panel/schematic.png]]
+
+Front panel case:
+
+[[file:front%20panel/front%20panel,%20front.png]]
+
+[[file:front%20panel/front%20panel,%20back.png]]
+
+Electronics fits inside:
+
+[[file:front%20panel/front%20panel,%20back,%20make.png]]
+
+Front view:
+
+[[file:front%20panel/front%20panel,%20front,%20make.png]]
+
+And attaches to the remaining components:
+
+[[file:front%20panel/attachment.png]]
+
+
+* Extra capacitors
+Another thing that become clear during load-testing: output
+power/volume can be further enhanced by adding high power capacitors
+to even out load on primary 20V up-step module.
+
+[[file:extra%20capacitors/extra%20caps.png]]
+
+Download:
++ [[file:extra%20capacitors/extra%20caps.FCStd][FreeCAD project]]
++ [[file:extra%20capacitors/extra%20caps.stl][STL file]]
+
+Extra caps are mounted on top of the speaker and electrically attached
+to the main board.
+
+[[file:extra%20capacitors/make.png]]
+
+* Center box
+
+Last physical part, to attach it all together: central body.
+
+Front:
+[[file:center%20box/front.png]]
+
+Back:
+[[file:center%20box/back.png]]
+
+Download:
++ [[file:center%20box/center%20box.FCStd][FreeCAD file]]
++ [[file:center%20box/center%20box.stl][STL file]]
+
+
+* Conclusions / TODO
+
+These things could be done better:
+
++ Instead of using undersized heatsinks on the audio amplifiers and
+ need for active cooling as a consequence, it would be better to try
+ to mount audio amplifier chip on top of speaker metallic body. It
+ would provide plenty of cooling and reduces power losses within
+ cable, since amplifier would be as close to the speaker as possible.
+
++ I used agile design. That is, implemented functionality ad-hoc. If I
+ had done design in advance, then I could have had smarter connector
+ layout between main board and front panel. That is: Instead of
+ multiple smaller cables, one wide (multi connector) cable.
+
++ Screw holes are too close to the edges on the front panel.
+
++ It would be better if screw heads were slightly buried within
+ construction body.
+
+
+Overall, it was good learning experience and I was able to test
+various ideas on it. Will add cooler later :)
+
+
+Photo of initial PSU + audio amp test:
+
+[[file:initial%20test.png]]
projects / physical.git / blobdiff