tb.music_box

DIY Portable Spotify Music Box

Introduction and Goals

Main requirements

• Portable Spotify Music Player
• Speaker power >=3W
• SNES Button interface

Drivers and Constraints

• Easy to assemble

• Very robust -> Mechanics and software

• Children friendly

• Good sound quality

• Portability/Low power consumption

• Sound quality over Portability/Power consumption

• Costs: <200$

System Context

• In/Out:
  • Display
  • USB
• In:
  • Buttons (SNES-Style)
  • Power supply
  • Power switch
  • Volume control
• Out:
  • Speaker

Decisions

Amplifier

• Stereo 3.7W Class D Audio Amplifier - MAX98306 + Klinkenanschluss: https://www.adafruit.com/product/987, https://learn.adafruit.com/stereo-3-7w-class-d-audio-amplifier, https://learn.adafruit.com/stereo-3-7w-class-d-audio-amplifier/inputs-and-outputs, https://learn.adafruit.com/stereo-3-7w-class-d-audio-amplifier/build-a-portable-sound-system, https://cdn-shop.adafruit.com/datasheets/MAX98306schem.png
  • Cheapest solution: https://forums.adafruit.com/viewtopic.php?f=19&t=144892, https://www.adafruit.com/product/1700, https://forums.adafruit.com/download/file.php?id=63172&sid=0f47a811efd81ec87bd2b66c538b6e77, https://learn.adafruit.com/adafruit-tpa2016-2-8w-agc-stereo-audio-amplifier?view=all, https://www.adafruit.com/product/1699
  • Uses Raspberry Pi (poor?) PWM Audio Out, needs some wiring, but receives good reviews

Speaker

• Speaker: 8Ohm, 3 Watt

Battery

• Lithium Ion Polymer Battery - 1S3P, 3,7V, 7800mAh

Case

• Self-made (wood)

Spotify client

• https://github.com/tbrandenburg/musicbox-spotify-client

Building blocks

Main parts list

Part	Link	Cost	Amount
Raspberry Pi Model 3 A+	https://www.adafruit.com/product/4027	25$	1
PiTFT 3.5"	https://www.adafruit.com/product/2097	44.95$	1
PowerBoost 1000 Charger	https://www.adafruit.com/product/2465	19.95$	1
Amp	https://www.adafruit.com/product/987	9$	1
Speaker	tbd.	tbd.	2
Li 1S3P, 3,7V, 7800mAh	tbd.	30$	1
Case	self-made	self-made	1

Button circuit

• The buttons are connected to RPi via 10kOhm pull-up

Knowledge

Impedances

Input/Output Type	Typical Impedance Range	Typical Voltage Range (Nominal)
Mic Level Output	50 \Omega to 600 \Omega	-60 dBV (1 mVRMS) to -40 dBV (10 mVRMS)
Mic Level Input	1.5 to 15 k\Omega	-60 dBV (1 mVRMS) to -40 dBV (10 mVRMS)
Instrument (Hi-Z) Level Output	10 k\Omega to 100 k\Omega	-20 dBu (77.5 mVRMS)
Instrument (Hi-Z) Level Input	47 k\Omega to over 10 M\Omega	-20 dBu (77.5 mVRMS)
Line Level (Professional) Output	75 to 600 \Omega	+4 dBu (1.228 VRMS)
Line Level (Professional) Input	10 k\Omega to 50 k\Omega	+4 dBu (1.228 VRMS)
Line Level (Consumer) Output	75 to 600 \Omega	-10 dBV (316 mVRMS)
Line Level (Consumer) Input	10 k\Omega to 50 k\Omega	-10 dBV (316 mVRMS)
Speaker Level Output	<100 m\Omega	20 dBV to 40 dBV (10 VRMS to 100 VRMS)
Speaker Level Input	4 \Omega to 16 \Omega	20 dBV to 40 dBV (10 VRMS to 100 VRMS)
Aux Output	75\Omega to 150 \Omega	-10 dBV (0.300 VRMS)
Aux Input	>10 k\Omega	-10 dBV (0.300 VRMS)
Headphone Jack Output	0.1 \Omega to <24 \Omega	N/A
Headphone Amplifier Output	0.5 \Omega to >120 \Omega	N/A
Headphone Input	8 \Omega to 600 \Omega	N/A
Raspberry Pi (PWM) Audio Jack Output	See Line-Out and note below	See Line-Out

Note: https://hackaday.com/2018/07/13/behind-the-pin-how-the-raspberry-pi-gets-its-audio/

References

• https://learn.adafruit.com/touch-pi-portable-raspberry-pi
• https://learn.adafruit.com/adafruit-pitft-3-dot-5-touch-screen-for-raspberry-pi
• https://learn.adafruit.com/raspberry-pi-radio-player-with-touchscreen
• https://www.reichelt.de/magazin/how-to/kodi-internetradio/
• https://learn.adafruit.com/raspberry-pi-as-a-media-center
• https://www.circuitbasics.com/setup-lcd-touchscreen-raspberry-pi/
• https://www.reddit.com/r/raspberry_pi/comments/3belpg/adafruit_pitft_kodi/
• https://www.opendisplaycase.de/opendisplaycase.html
• https://www.opendisplaycase.de/tutorials/raspberry-pi-raspian-tft-displays.html
• https://www.opendisplaycase.de/opendisplaycase/up-board-kodi-mediaplayer-box.html
• https://en.wikipedia.org/wiki/Line_level
• Can You Use The Headphone Jack with the MAX98306 amp?: https://forums.adafruit.com/viewtopic.php?f=19&t=144892
• http://www.sengpielaudio.com/Rechner-EingangsAusgangsWiderstand.htm
• https://www.pcwelt.de/ratgeber/Digitalradio-mit-DAB-9733609.html