PROTOTYPE:

Chair:
I used a stool from the shop. It isn't as awkward as it should be,
but for the purpose of testing the electronics and concept, it will do
just fine.

Communication:
I used an XPort combined with a PIC 18F252 for communication. The
XPort automatically logs into a JAVA-based chat server hosted on a
computer at ITP. The PIC program parses commands sent through the
chat program and relays sensor information back to the chat, all via
the XPort.

Sensing:
I had another PIC 18F252 hooked up to an audio preamp and a light
sensor. The light sensor was strapped onto the top of the chair to
sense occupancy. The preamp circuit utilizes a LM386 chip and a $3
radio-shack condenser microphone. This setup is capable of detecting
basic noise levels. I had to do a lot of coding to get an accurate
representation of the ambient noise levels in the room.

The code can be found here: Communication,
Sensing.
The preamp circuit can be found here.

Inter-PIC Communication:
One PIC handled sending and receiving commands from and to the XPort.
The other PIC analyzed information from the sensors. The sensor PIC
was constantly broadcasting its information serially. The
communication PIC would listen to the sensing PIC when it received a
request from the chat for sensor information. Getting the PICs to
talk to each other required only a few lines of code on each PIC:

On the Sensing PIC (Send):
serout2 picTx, non9600, ["P"]
serout2 picTx, non9600, [soundLevel]
serout2 picTx, non9600, [occupied]

On the Communication Pic (Receive):
SERIN2 adcPicRx, non9600, [WAIT("P"), adcPicByte, adcPicByte2]

Pictures:

1. Photocell
2. Audio preamp with microphone and PIC.
3. XPort with PIC

CONCLUSIONS:
A friend of mine thought this was a terrible business idea. I'd never
considered thinking about my project in a business sense, so his point
was interesting. My device benefits the consumer and not the coffee
shop. There is no reason for the coffee shop to purchase such a
chair. It would only keep people out of the café. My intentions with
this project were to realize an idea that would be well thought-out
and generally useful. However, I suppose that if I'm thinking in
practical terms, the next level might be to think on a business
level—apparently, looking at ideas economically can illuminate facets
that I otherwise overlook.