Motorola Bluetooth And Texas Instruments And Audio Blimps
In this installment, Casey walks us through how they created the whole setup; including directing the audio and controlling the blimps. The tupperware blimp gondolas don't necessarily look all that impressive at first, but they're filled with hacked hardware. Each blimp has a Motorola bluetooth receiver, and a Texas Instruments Class D amplifier. Everything was chosen not only for its performance, but obviously for its relative weight, since at the end of the day everything had to float.
Casey explains how they used a MIDI controller (designed for a modular synth) to convert the control voltage to move the blimps. It was a kind of control, anyway, since the team also had to deal with spin and the fact that the blimps weren't floating in a vacuum.
It was an intriguing evening, with all of Casey's friends, passers-by and random local kids who had stopped by the Armory to play basketball, but instead walked into a sound experiment. That's neighborhood art at its best.
Hear all the details in the Gearwire video.
CASEY FARINA: The basic system involved controlling, we want to be able to control all the blimps from the computer.
[CASEY FARINA AND CREW CONTROLLING FLYING SPEAKERS]
And we definitely achieved some of that. Essentially, what we were doing is we were using multichannel Bluetooth technology to these guys. Essentially, it looks like a little MP3 player, but this is a Motorola Bluetooth receiver, a class 1 Bluetooth with the A2DP protocol. So, class 1 Bluetooth is 100 m of wireless transmission so it’s 300-some feet so that was going to be enough for our purposes.
[CLIP OF PROJECT CONDOR IN ACTION]
So each blimp has one of these guys on it, and then we also had wireless Bluetooth transmitters for each channel of audio. So, we had a multichannel digital box on a computer, outputting eight channels of audio and streaming wirelessly to each computer -- to each blimp rather.
[CLIP OF A PROJECT CONDOR FLYING SPEAKER IN ACTIVE USE]
And then the -- where we control the blimps from the computer that we hack to the controllers, which actually operate on a 0- to 5-volt control paradigm. So otherwise you move the joystick to the left or to the right, it’s usually at 2.5 volts, and if you move it to the left you get a zero, and if you move it to the right you get a five, which is actually the same kind of control paradigm that you use for analog synthesizers, fortunately.
GRETCHEN HASSE: Oh. Yeah.
CASEY FARINA: So, we essentially just wired ourselves into the controllers and then used a MIDI-to-control-voltage converter designed for some sort of Moog or Buchla modular synthesizer and we were able to use MIDI information to convert to control voltage to control the blimps.
So, this is the basic blimp/gondola setup. Essentially, these are Tupperware containers...
GRETCHEN HASSE: Right on.
CASEY FARINA: ...as a modified gondola. A lot of the project -- I had an idea of what I wanted to accomplish. I wouldn’t really call myself any sort of roboticist or anything like that, so it wasn’t like I could design a lot of this technology from scratch by myself. So, we tried to make use of a lot of, you know, sort of invert the usage of things that were already available to us in order to get it to work. So, we made the gondolas out of Tupperware, sort of burnt holes in them with soldering irons, and this over here is the speed control for the blimps. All of the motors get wired into this. Each blimp had three motors, one of the left and one on the right and one on the bottom. So, we control them sort of tank style.
GRETCHEN HASSE: [LAUGHING]
CASEY FARINA: If both of them -- both motors forward, there’s forwarder, forward, both motors backwards, there’s backwards, and then left one forward, right one back, it’s turn and turn the opposite direction, and then the bottom motor gives us elevation; you can send it up or send it down.
GRETCHEN HASSE: Okay.
CASEY FARINA: And this was receiving information from its standard controller that was being controlled by our control voltage converter.
GRETCHEN HASSE: Okay,.
CASEY FARINA: So that gave us the ability to control the blimps -- control multiple blimps with the computer.
GRETCHEN HASSE: Okay.
CASEY FARINA: Over here -- oops.
GRETCHEN HASSE: [LAUGHING] [INDISCERNIBLE] [LAUGHING]
CASEY FARINA: On the other side is the amplifier...,
GRETCHEN HASSE: Okay.
CASEY FARINA: ...the -- our Bluetooth receiver plugged into this guy here.
GRETCHEN HASSE: Mmm hmm.
CASEY FARINA: So, just a regular 1/8” audio connection.
GRETCHEN HASSE: Uh huh.
CASEY FARINA: And we’re using these Texas Instruments class D amplifiers. Really clean and also digital amplifiers so there’s no need for a heat sink, which obviously would have increased the weight...
GRETCHEN HASSE: Oh yeah. Yeah.
CASEY FARINA: Quite a bit. So, everything -- all the decisions we made about the things that went onboard, you know, the first consideration all the time was, you know, what’s the smallest, lightest stuff we can find? And these worked out great. So, these run off of Lithium polymer batteries.
GRETCHEN HASSE: Mmm hmm.
CASEY FARINA: And they were wired to these custom made speakers that I ended up fashioning. Once we knew we had quite a bit of lift, over 5 pounds of lift that we could use standard speaker drivers. So these are 10-band, excuse me, full-range audio drivers and we needed to fashion a speaker cabinet for these things though, and we knew we couldn’t use wood or plastic or anything like that, so this is actually Styrofoam, insulation Styrofoam, and so I built all these speaker boxes out of Styrofoam. They weigh less than the speaker drivers do themselves. So, that was the way we can get two speakers on each blimp.
And then this is the bottom motor, so that’s giving us the up and down thrust.
GRETCHEN HASSE: Okay, and then the other actual propellers were on the blimps themselves?
CASEY FARINA: They were on the sides of the blimps, yes.
GRETCHEN HASSE: Okay, and the blimps are made out of like what are they?
CASEY FARINA: Uh, just some sort of polyurethane membrane.
GRETCHEN HASSE: Mmm hmm.
CASEY FARINA: Like a little bit tougher that beach ball material.
GRETCHEN HASSE: Okay.
CASEY FARINA: They -- I think they’re intended to be used as I think gigantic inflatable balls like you use it like a car dealership or something...
GRETCHEN HASSE: Oh. Okay.
CASEY FARINA: ...to advertise on Saturdays or that kind of thing.
GRETCHEN HASSE: [LAUGHING]
[CLIP OF A PROJECT CONDOR FLYING SPEAKER IN ACTIVE USE]
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