Does anyone have any suggestions on how to broadcast TTS out over the civic bus interchange for 3x one hour blocks without breaking too many banks or too many laws?
Are you using the Infrastructure that’s already there (PA/Emergency-PA) or are you planning to add your own?
I think it’s doable… just need more info on what the rules are.
Is it a permanent installation? or Mobile? For example if it is something akin to a Political Broadcast (which I’d understand would be allowable) ?
Very unlikely we can use any infrastructure that’s not publicly available. Eg. the existing PA system is out, but the cbrfree wifi network is in, any RF that we can push without a licence is in.
It’s for 3 performances of an Art; we won’t be leaving anything behind. We can have artists hold on to the systems (maybe even wear them), but something that could be somewhat inconspicuously placed would be ideal.
Lately I’ve been contemplating some “$foo over wifi SSID becaon” shenanigans. You could build a protocol to broadcast text around changing SSID names (beacon frames). Then you could literally text-to-speech the broadcast text 
… admittedly, that’s a lot harder than CBRFreeWiFi for not much gain.
There’s also some fun optical communications experiments out there, http://modulatedlight.org/optical_comms/optical_index.html is a good resource but probably too much effort again.
This comes down to budget and time. It’s going to be hard to beat hacking something like http://www.ebay.com.au/itm/301440854360 although you’ll have to monitor and be able to change freqs in case of other users on the air. UHF CB rules are pretty broad http://www.acma.gov.au/Citizen/Consumer-info/All-about-spectrum/Marine-and-Amateur-Radio/citizen-band-radio-service-cbrs-fact-sheet
I like this UHF radio idea. Is it easy to come get one of those to take line out from a computer and automatically do the PTT thing when signal comes in?
VOX PTT circuits can be fiddly to adjust and get right but there’s plenty of designs out there, I’ve just never built one from scratch. Here’s one of the simpler ones: http://www.rason.org/Projects/basicvox/basicvox.htm
I’d be happy to help.
Matching the line out to mic input impedance should be fairly simple also.
I’d probably watch the audio in the radio at wherever we intend to inject the line out, with an oscilloscope, and make an OP amp circuit to transform the line out to whatever is needed. And hopefully you only need one or two such radios with the rest being receivers.
For the Pacific Games in Port Moresby they had a small FM station and all participants in the show (the ones you saw dancing and the like) had small cheap receivers on them. Don’t know if it helps, but it should be easy to get some license for a day if you feel you need it ?
It is very agricultural compared with Paul’s proposal, I know, I know…
Paul, VOX thresholds are a pain. I would go for a syllabic squelch, although you have to buffer the audio somehow because the circuit will have a delay and the first hundred miliseconds will not be transmitted (it has some “reaction time”).
For a pure txt to speech application, the computer can transmit a brief burst tone before every message (say, 8 kHz for 100 ms). You detect it, activate the PTT, and off you go. No need to remove the 8kHz tone as the CB radio does not get that far in the baseband. Another tone at the end finishes the transmission. Or the PC simply puts the speech with the tone superimposed all the time, like the In-Band tones used in the ATC radios when they use leased phone lines (in this case, 8kHz is an “Out-Band”).
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Yes I was thinking of some activation delay/hysteresis, maybe with a 555. Love the 8khz tone idea, unsure if it fits the use-case (not sure of Adam’s detailed plans 
any Digital alternatives?
I have some ESP8266’s and this project looks interesting : http://hackaday.com/2015/06/06/esp8266-as-a-networked-mp3-decoder/
Also, I have a drawer full of LM386 and a drawer full of some other D-Class Amplifiers. I think they’re about 20W.
I guess I will bring what I have along on Wednesday to Electronics night. I’ve also got a storage-box full of speakers.
How is this being deployed? how many nodes?
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This is not an answer as quality is missing, but remote computers permantely connected by ssh could use espeak
It’s a one off prank you can play on your wife/partner’s computer while she is using it.
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Speakers for 100m diameter will need a shopping trolley, at least, to move them around. Maybe even something better than that.
Although there are smaller, more compact products:
That’s a lot of AA batteries 
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So far the Mini-Mitter FM Transmitter is at the top of my research tree - http://www.jaycar.com.au/p/KJ8114
Plus a bunch of FM radios
I will bring a battery spot-welder along tomorrow night and we’ll see how many batteries we can spot-weld. It shouldn’t be an issue.