Music and Lights on a Bicycle I

Welcome! to my first blog post! One of my friends told me about this mass cycling musical event called the Bike Rave, where people decorate their bicycles in glowy things and simultaneously play a pre-selected mix on their bicycle speakers while riding around in the city. Sounds super fun! So I am planing to check it out this year.

So I decided to turn this into a project and build my own speaker and lights system. I found two 8Ω speakers around the house, which looked like they could produce some decent sound. Great! what’s next? I am planing to play the music from my phone. However, the audio output of the phone doesn’t produce even close to the amount of power required to drive the two speakers. I need an amp that can deliver around 10W to the speakers.

Searching around online I found a suitable candidate, the LM1875 IC. I went with the LM1875 because

  • It can produce up to 30W output power (more than enough for the speakers I got)
  • price & availability (it cost only $3 at the electronics store and was already stocked)

The most important thing to be aware of when using the LM1875 is to use a heat-sink, even when no load is connected to the output. It does have thermal shutdown, which is a good thing.

So my first step was to see if I could drive the speaker with this IC. So I picked one up and wired it out on my breadboard according to the schematic in the LM1875 datasheet for operation with a single power supply (see below). For powering the IC, the +12V supply I made in my Electronics class at school came in handy. Flip the switch, and connected it to the audio output of my phone and it worked beautifully!

LM1875 audio amplifier schematic for single supply operation. Schematic taken from the LM1875 datasheet.

The next step is to work out the lights! I will leave that for the next blog post!

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