ED BENNETT: I'm Ed Bennett, and I'm the research specialist in the Art and Technology Department, and we're going to look at the context and tools that we used to develop the ArtBus project and explain like why it's here and what it does.

These are little photo cells and they talk to a PD patch, and I think there may be another piece of software in there. Ben has an X description of it, but the photo cells talk to PD, and PD does this granular synthesis and it's sensitive to which way you're walking down the hallway, so if I go this way then I get -- the thing responds to me, and it has all these different kinds of moods and behaviors, rather different characters but it always has the characteristic of the granular synth. It's making that one sound right now but it has all kinds of ideas of about what it should be doing.

GRETCHEN HASSE: And it's also reacting to me, walking by it too.

ED BENNETT: Sure. So, this is the ArtBus board. There's one nmore of these panels but there's 16 channels of input and they are reading -- catch that as I walk down the hallway, and you can see that's what's PD is taking for input as I go down the hallway, so that's the data input to PD.

A quick tour of the hardware. So, this is the USB cable coming out of the laptop, and this is an FTDI development module, and this is the serial protocol that we use the hardware level. It's called the RS485, and this chip converts the FTDI to RS485. There's four wires on this connector; it's ArtBus in and out here. Two of the wires carry 5 volts that are running the board. That five volts is borrowed off of the USB bus. The other two wires, the middle pair, actually carry the data, and it's bidirectional. So, technically it's a single master half duplex protocol, so the line carries input and output but only one device can speak at a time, and there's one device that controls who can speak and that's the bus master. So, whatever is on the other side of this cable right here is the bus master, so anything that plugs in here.

So we have Processing, Flash, Max, and PD right now that can be the bus master, but the bus master is actually a hardware concept. So this is not an in and out; it's a bus so these wires just run straight through it. Al four wres here just run straight through, so you can flip the plugs if you want; it works the same way.

So, the initial idea behind this was to have a long run of wire in a large installation space, and so I'm playing with that idea right here by having a long cable that just shows the fact that that's part of the intent. When we package these up as kits for the classroom, we include little short cables, but this is just for fun right now. The boards can get their 5 volts from anywhere, so the outside pair is the 5 volts. If you wanted to, you can make a two-conductor arc bus cable and power the board locally so that as you want from board to board you can have kind of wall-warts throughout your space and not have to drag your USB power line all over the gallery space.

The maximum -- I don't know how many boards would ever want to hook up but you know, eventually you run out of power from USB so you'd want to supply 5 volts anyway. So, this is the bus going from this board to this board. If you have a really long run of wire, there's a terminating resistor behind there, and you put a jumper in that hole, and you get termination, but this is fairly short and you don't have to do that. RS485 is supposed to be good up to like 3,000 feet or something like that although I haven't done -- I haven't pushed it to see where it breaks

This is a PIC16F690, and it's clocked at 20 Mhz. This is the RS485 conversion. So I guess that is the extent of the hardware.