Voice over CAT5

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Hi,

My wife runs a horse show once a month. There is an announcer's stand and a judge's stand and the 2 need to communicate with each other constantly all day. Originally there was an intercom system in place that communicated via CAT5 cable. It allowed the secretaries booth, the announcer's stand and the judge's stand to all communicate with each other. This thing required you to push the Talk button and then a 2 digit address (to select the person you wanted to speak with). You were required to push an End button when you were finished speaking. This was too much trouble for the judge and announcer. Then we tried 2 different brands of Walkie-Talkies. One had too much interference no matter what channel you selected and the other just started to intermittently "eat" batteries.

I decided I would try to build a direct intercom between the judge and the announcer using the CAT5 cable already installed. I found some information regarding balanced line drivers here:

http://sound.westhost.com/projec...

How important or is it important for the CAT5 cable to be shielded twisted pairs vs. just twisted pairs? The distance to communicate is approx. 250' (83 meters).

Also, if anyone has links they could post regarding a simple 2 station intercom that operates over CAT5 I would be interested in seeing them. I have searched and it seems all I can find are complicated systems meant for multiple stations. I have also searched for DIY projects but haven't had much luck. I used "audio over ethernet", "audio over CAT5", "CAT5 intercoms", "voice over ethernet", "voice over CAT5" as search terms.

Thanks,
Steve

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When you say CAT5 are you looking for a solution involving TCP over IP over Ethernet over the CAT5? If you put a Wiznet module in each unit you could ADC/digitise speech, then TCP or UDP it to the destination device where you DAC/PWM it.

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Judging by the posted link, I'd guess that Steve is looking to send good old analog audio over a twistd pair.
I've not done this myself, but I'd guess that, while shielding might make a difference, the whole idea of differential drivers is to cancel out the external crap that wires pick up. I don't know what happens when you add a common ground, though(as RS484 networks often seem to).

Four legs good, two legs bad, three legs stable.

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Sorry, should have been more clear. Definitely not TCP over IP over Ethernet...way, way over my head.

@ John
The reason I was confused is because the source I linked to and another source indicated you didn't have to use an overall shield. However, the datasheet to Burr-Brown devices (DRV134 and INA134) shows an overall shield in the applications section of the datasheet. I am kind of hoping Burr-Brown was just covering their arse.

Thanks for the responses,
Steve

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Sending audio over crappy copper lines has been done for ages. Depending on the source you believe approximately since 1876, if you get the hint.

If you don't get the hint, the thing is called a telephone.

Forget that modern junk. A two "station" "intercom" can be build from just two old-fashioned analog phones and a voltage source (battery).

If you need more "stations", I would shop around for a cheap analog PABX. At some point in time those were available new for less than 100 Euro, and the size smaller than a cigar box, but they have gone out of fashion.

Stealing Proteus doesn't make you an engineer.

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A good quality PA (100-12k or so) sounds a lot better than phone quality (300-3k). This is sort of the domain of 'pro audio', so you need a little powered mic mixer at ea end. Mic mixer sends a 0dbm line level output to the other mixer's line in, all balanced on cannon mic cords, and there is a speaker with a volume control, and its all full duplex and second source. A balanced line level signal should go 1000 ft no prob. Look at a mail order place like mcmelectronics for mic mixer. See the xenix behringer 1204? Back view shows the balanced line out that will run to the other station. Use an amp with mixer at ea position.

Imagecraft compiler user

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If you do not need to run power over the same pair as the audio, add audio transformers at both ends. This is also the approach you find inside good audio gear in ports that do not have phantom supply. This gives you have a floating balanced driver at one end, a differential receiver the other end, and takes care of balance mismatch to ground. This is good enough to get proper audio across, and I have run stereo+video over the same arrangement without being able to detect leakage from the video into the audio.

If you get into lines that are long enough that the resistive loss in the cable starts hurting your frequency response, loading with the cable's characteristic impedance at the receiving transformer may help. But that is usually >>100m.

For transformers, rob a few analog modems.
And 'good' does not include single ended inputs.

/Kasper

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70Volt audio. Commonplace for small gauge, long wires. Transformer to drive 8 ohm speaker.

Search web, such as
http://www.alectrosystems.com/au...

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I'd try the two random telephones and battery idea first.

You don't need specialized audio chips to drive or receive differential audio, you can just use regular op-amps for that. TL074 should do it.

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With two two POTS Plain Old Telephone'S, you will only use one of the four pairs in the CAT5 cable. The telephone does the two wire to four wire conversion.
You will need a transmission bridge in the circuit. A simple bridge will be two resistors of about 270 Ohms each connected to one side of the line & the other side connected to say 12 Volts.
You will not be able to ring each other, but once both have picked up you will have a good quality audio cct. No electronics required.

Charles Darwin, Lord Kelvin & Murphy are always lurking about!
Lee -.-
Riddle me this...How did the serpent move around before the fall?

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Thanks everyone! Now off to find some old fashioned telephones.
Steve

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Years ago we used to use telephones as intercoms. Just need a way to limit current.

You can also rewire the hook switches and use a couple of extra conductors to buzz a low voltage annunciator.
Pick up one handset, and the other one buzzes until you pick it up. And vice versa. (Well, we used lights because the stations were usually in a audio booth.)

-carl