Jukebox. Intro. Choosing components

 For last couple of month I'm working on a project which I call "Jukebox" - a portable player for my 2-year old daughter.

The project was inspired by Phonybox.de project but I decided to start from scratch to learn all the basics.

The idea is simple: kid can play songs by placing RFID-cards onto the box.
It is hot it works now:





 

That's the initial Idea for the project:


Components selection

Since I do such a project for a first time, choice of components is relatively random. Some are based on the availability, some on price, some on number of number of mentions in the Internet.

Main control unit

 I've decided to build system around Raspberry Pi:

  • I already had one, and have some experience with the platform
  • Bigger versions of raspberry pi (3B+, 4B) have audio-jack on board
  • has WiFi for remote access  (to upload content, update soft)
  • has GPIO (for buttons and hardware control)

RFID reader

There are many modules based on MFRC522 chip, often referred as RC-522. These ones are quite cheap an often are shipped with compatible cards. I've ordered a package of 3 modules, 3 cards, and 3 tokens. 



 


Speakers

Speakers and amplifier have to be selected together. What parameters to look at:

  • Impedance. Typically amplifiers have specification, what range of impedance they support. For speakers it's just a fixed number. Typical values here are 4Ohm or 8Ohm.
  • Power The amplifier output power shouldn't be higher than speakers one. Otherwise speakers can be damaged. If amplifier power is less than speakers, it means you can not use the whole "capacity" of speakers, but it won't harm anything. Note that with power more than 3W per channel, you may need more than 5V power supply.
  • Input voltage for amplifier. The raspberry pi is powered by 5V so it' would be handy to feed the amplifier from the same source.
  • Size speakers can vary in size. So, ensure they fit the housing you choose.
  • Frequency range there are  designed for producing sounds of only narrow sound range, they are intended to be used in the bigger sound systems, with different speakers for different ranges. For our needs we need a "Wide range" speaker, which will produce as large sound range as possible (we hear from 20Hz to 20kHz, but for our purposes something like 200Hz to 15kHz should be fine).
I've selected a pair of 5cm 2W speakers to make stereo device, and a DIY amplifier set.


Powerbank

The bigger the better. There is a couple of features to consider, but they are not typically mentioned in descriptions.

  • If power bank is connected to the power supply will it still provide electricity? For us is better if it would, then we can charge while the device is turned on.
  • Does it require to push some buttons to turn on output electricity. Some devices require to push the button to turn on the output. It doesn't suite well our needs. There are devices which turn on, once load is connected.


 

Hosing

The device should look at the end as a toy. So look up for something, what can fit all the components. Wooden boxes suite well this purposes. I had one as packaging for a present.

Other

Of cause to build everything together you will need some smaller components as well.

  • Wires
  • Audio jack 3.5mm you need 3-pole jack
  • Stereo Potentiometer

Result

That's how it looks everything together. The components are glued with hot glue or double sided tape. The photo is taken after a couple of iterations and improvements, which I hope to describe later.


 


Location: Munich, Germany

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