Help me make the crowdsourced sentient sculpture of my dreams.
March 29, 2019 11:19 AM   Subscribe

I'm trying to design an interactive outdoor sculpture consisting of two sites placed about half a mile from one another across an open landscape. I'd like each to have microphones and speakers, such that people standing at one site can hear and talk to people standing at the other without having to touch or otherwise activate the technology. Bonus fun: I'm in a remote location with unstable (or at least not-guaranteed) access to cellular or network service. Assume I have access to generator power. Technically speaking, how can I pull this off?

Avenues I've considered:

- Two-way radio (Not ideal, since the mics need to be "open" at all times - I don't want participants to have to deal with a button or anything to press to open a channel. They should be able to walk up to the site, hear all the activity going on at the other site, and speak into it hands-free.)

- Low-power FM (Transmit-only, plus the distance is far too long to fall within current legal LPFM limits.)

- Some kind of tiny Raspberry Pi solution involving Mumble or other VOIP/conference software (This is contingent on having some kind of dedicated/reliable cellular data service, since we will be miles and miles from other telecom infrastructure, but I'm willing to entertain the possibilities.)

This question at the Raspberry Pi forum kinda gets at what I need, except I'm not interested in video.

Interested in any possibilities involving the above, and/or hacking some entirely different platform.

Thanks for the creative thoughts!
posted by mykescipark to Technology (7 answers total) 1 user marked this as a favorite
I instantly thought of two parabolic dishes. There used to be a set up at the Science Museum in London years ago where you could speak to people across a massive (and noisy) hall. Like this - I guess if they're big enough that distance could be crossed?
posted by atlantica at 11:40 AM on March 29 [4 favorites]

Do you have line of sight? 1880's Photophone technology would work. Or update it to use lasers. Or use 2 sets of walkie talkies, each at a different frequency, with one mic switch on each pair replaced with a toggle instead of the momentary contact.
I suspect your major issue will be controlling feedback.
posted by Sophont at 11:58 AM on March 29

You could look into long range WiFi equipment, like the systems Ubiquiti sells. You can run it entirely self contained without any internet access.

The thing I linked was over $1000 but if you're only talking a half mile you could probably use something cheaper like their Nanostation or rocket and get it done for a few hundred bucks.
posted by Nonsteroidal Anti-Inflammatory Drug at 12:34 PM on March 29 [1 favorite]

I don't want participants to have to deal with a button or anything to press to open a channel.

There voice-activated transmission (VOX) circuits which trigger the transmission when the voice volume is sufficient. Expect to have to play with levels and microphone/speaker position to avoid audio feedback.

I like Sophont's idea to use modulated laser light instead of radio. Otherwise, with radio, you would want make sure you are operating legally with regard to the radio emissions and licensing.

If you do wind up using radios, you can make or buy highly directional antennas that will improve performance between the two stations. For example, I made an antenna out of an old tape measure and a few dollars of PVC and used it to listen to satellites orbiting the earth.
posted by exogenous at 12:46 PM on March 29 [1 favorite]

NSAID has the right idea. Here's a pair I've used. Assuming you have line-of-sight, they'll work.

If you're considering a RPi based solution then you probably have enough knowledge that these'll be a cinch to set up. It's a lot like configuring a WiFi router. You'll need 24 volts, or AC if you use the included adapter.

I've run one of these off of 12 volt solar/batteries with a boost converter, on top of a water tower, at a distance of 5ish miles, for years.
posted by Horkus at 9:41 PM on March 29

To expand on atlantica's comment acoustic mirrors (like the parabolic dishes at the science museum) were used to detect aircraft before radar. This site claims that they could detect aircraft 6.5 miles away, which makes me think that voice transmission over half a mile should be possible. While they are going to have to be big and require some precision to set up, once they are set up they will need zero power, and almost no maintainence - you can look at this set (voice communication over only 23 metres) to see how extremely simple they are. That last link also gives the name of the company which made it, which could be an avenue to enquire about the fiesability of this over a much greater distance.
posted by Vortisaur at 5:00 AM on March 30

Lasers are a PITA unless your mount is really stable (or they're better now). We used a laser bridges for a while before WiFi was a thing and mounted on buildings and wind etc... there were many 2am calls to get two people out and re-align the lasers. The focused long range WiFi is your best bet. Microwave links are probably overkill.

If you can trench, you could run fiber. Difficulty is more along the lines of how long you want it to last. You might be able to get away with burying some fiber a few inches under the soil and a couple of transceivers on either side. Depends on what's in the way on that 1/2 mile path.
posted by zengargoyle at 1:10 PM on March 30

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