Transistor Audio Light

A little over a year ago, after my experience in our Introduction to Mechanical Engineering course, I started playing with electronics. I had a lot of random electrical components left over from the class and my robotics project in addition to the components included in the kit for the Introduction to Circuits class that my roommate had around (I had not yet taken the course). I didn’t want everything to go to waste, so I started thinking about what I could do with some of the components I had.

I came into college as a Chemistry nerd majoring in Chemical Engineering. I took Organic Chemistry my first semester Freshman year and quickly decided that ChemE was not the right field for me. I ended up changing my major to Mechanical Engineering. What I’m getting at here is that the world of mechanics and electronics was completely new to me. I was never involved in robotics teams and never felt the need to take things apart and tinker; I was more excited about lighting things on fire and watching chemicals react. Seeing how much some people knew and how much they could do with just motors and cheap electronics amazed me and ultimately inspired me to start this project.

I took it upon myself to learn a little more about electronics, even though this project wasn’t too complicated in the end. I thought about what kind of things I could make that would be able to be used around the apartment, and since my roommate had been playing a lot with LEDs at the time, I decided to make a bottle lamp where the LEDs pulsed with the music.

The first thing I did was figure out what components I would need to actually make the lights pulse — turns out the only thing I needed was a transistor. We had a TIP131 transistor, so that’s what I ended up using for the circuit. I did need to make a quick run to Axman for this project to pick up a battery pack (to hold 4 AA batteries) and some speaker wire.

The circuit diagram below is essentially how I wired the circuit, but the program I used to draw this schematic only has a limited selection of symbols so some components are not what their symbol suggests. The voltage is representative of the 4-AA battery pack, and the speaker symbol represents an audio jack. I only used three LEDs in this schematic, but the final light had 10–15 LEDs wired into speaker wire to provide more of a light source.

In the end, this didn’t turn out to be as complicated of a project as I had expected it to be. The hardest part was honestly jamming all of the LEDs into the speaker wire — it required some serious fine motor skills, and I kept messing up or breaking the “legs” of the LEDs. My final product did turn out and was really neat — it was a great conversation started when guests came to the apartment and I had many requests to make more as gifts!

The version I made requires that the audio jack is hooked into a media player (laptop, IPod, etc.) and needs external speakers to play music. In the future, I think I’d wire a speaker to the circuit so “less assembly is required” whenever I want to use the light — that way I only have to plug the jack in and press play (as opposed to hooking it up to the music source and using a splitter to hook in speakers).

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