Starting on the audio system

I received a pair of computer speakers from Jan and Shannon to use on the project. I took them apart, removed the electronics, put some expanding foam in the tuned ports (to help waterproof them) and painted the speaker cones (again for waterproofing.)

I took a look at the parts I have and figure I can just make a daughter-board for the MP3 player which would control its operation, provide power, and contain the audio amplifier. I decided to use a comparator to detect when there's a signal: compare against some small positive voltage and send the output to charge a capacitor through a diode which would discharge with a high R-C time constant. When the capacitor voltage drops below a set level, a second comparator would trigger the play button to be pressed.

I got back to working on the amplifier and started looking at the TDA1520A because I have several lying around — they're a 20-watt mono audio amplifier chip that requires very few external components. Unfortunately, the designers decided to neglect the car-audio market and it's rated to work as low as 15 volts. I figured I'd try it with 12 volts … I wired it all up and found that it just wouldn't function right. Darn.

It dawned on me that I should just use the amplifier from the computer speakers — it's already wired up, it's designed to work with the specific speakers, and it originally ran off 9 VAC so I can get about the same using 12 volts into the AC input … admittedly with some superfluous components, but who cares?

I decided to use telephone jacks to connect the speakers to the main control box as they seem to be easy to make water resistant I sealed up the holes on the speaker cabinets and prepared them for a phone-wire connection.

I took apart the MP3 player and connected wires to the play button and to the data activity light. The activity light pulses around 1 volt whenever the unit is playing, and that should be easier than detecting audio output. I set it up with a connector to plug into a board and I set up a metal bracket to hold the amplifier board, the MP3 player, and the auto-start board. I added DC-blocking capacitors between the MP3 player's output and the amplifier input as the DC levels are likely to be different and the system wasn't designed with a common ground in mind.


Upholstering 101

I had picked up a couple futon mattresses from the trash. One of them was red on one side and black on the other. I separated the two sides and pulled all the stuffing out — it's cotton batting that wraps around three layers of urethane foam. I cleaned the pieces of fabric.

I used plywood for the seat bottoms and back, cut to fit the mounting holes. I cut pieces of foam and wrapped each in batting then cut sheets of red fabric, wrapped them around the seat-side of the seats and stapled it all in place. I just kept finding where the fabric was slack, pulled it tight, and stuck in another staple.

In my mind I wanted something like lips which is why I picked red. I decided to cut notches in the seat back to imply lips. I want to maintain the industrial-organic appearance and very fluffy, organic-looking lips would seem out of place so I gave the "suggestion" of lips. I haven't had a chance to put it together to see how it looks.