Sunday, November 13, 2016

External Speaker

I don't intend to write a whole how-to about this project, but I still want to share a bit more than just a few pictures.

The Plan

What I made is an external speaker with built-in amplifier to use with your laptop, smartphone, mp3 player, etc.
This project started out differently. I actually was thinking of building my own internet radio. Just by pressing power on I would get my favorite radio stations that I can't hear on FM because they are too far away. Since I already had a Raspberry Pi 2 laying around I thought of using that. I also had some decent old speakers. All I needed was a proper amplifier to get the sound out louder and then I would try and cram everything inside of the speakers, with buttons and knobs on the outside.

This is when I bought the Adafruit Class D Amplifier which only requires some soldering to get it to work. I put the amplifier together and tested it worked properly. In the meantime I was thinking what else I would need for this project. This was really a project where I hadn't thought everything through before hand. The more I was thinking about it the more I came to the conclusion that the internet radio and the speaker with amplifier should be separate things. I would rather have the amplifier for more than just the internet radio.

The finished speaker

So I made that decision, only the amplifier inside the speaker.
To make this possible I needed do some more shopping:
  • variable resistor 1kOhm
  • a knob to fit on the resistor
  • audio input plug
  • power input for my 9V power adapter
  • connectors
  • on/off switch
  • power on LED
  • audio connectors for a second speaker

Not so difficult, but messy IRL

Everything worked fine when connected, but I still needed to get it inside the speaker.
My speaker had no clear way of removing the wooden outside so instead I removed the front cover and screwed out the speaker itself. That gave we a large hole the access the inside, but it's wasn't ideal to say the least. I wanted to place the volume control and audio input on the side and the on/off switch+LED on top. The power input went in the back together with the connector for a second speaker.


Drilling holes from the outside is easy, but... the side panel turned out the give me some headaches. The wire on the variable resistor and on the audio input are both very short and that meant that around the hole I had drilled I needed extra space on the inside. I don't have proper tools for that so I had use a wood drill bit by hand until the elements stuck out far enough so they could be tightened with a bolt. That work costed me a lot of time and made me wanna quit the whole project all together at certain points. But at last everything worked out and on the outside it looks quite good.

Variable without knob and audio input

I made sure I had pretty long wires on every component. What I should have done was mark what every wire was. I now had to place all the components in their position and then reconnect all the wires again. So sometimes I had the feel where a wire was coming from to make sure if I was connecting the switch or the LED (big difference). When I had tested the system still worked pushed everything back in gently and used some hot glue to attach the amplifier to the bottom.

So this must actually be the most usefull thing I have ever built :) The sound is pretty good and the volume is good enough for me. We use it to listen to music and when watching a movie. Worst complaint I have is that it hums when a YouTube video ends on my phone. Also some laptops output a weird balans making movie sound as if it's covered in pillows. We needed to shut of the Dolby Surround to solve that.

Anyway, I'm glad how the project worked out. Any questions are always welcome.

Some pictures

Power input and audio connector for the second speaker