Use existing telephone lines for sending serial data?

[Leros]

Would it be possible to utilize existing telephone lines in a house to have two device communicate via serial?

 

[bobsmith1492]

Would it be possible to utilize existing telephone lines in a house to have two device communicate via serial?

Are the lines already in use? If so, you'd need a modulation scheme like a DSL modem. If not, then go for it - they're just wires.

 

[PottedMeat]

^this, if the house is fairly new there should be unused pairs.


i'd try RS232 for <50' ( at least 3 wires ), or try RS422/485 for up to 4000' ( 2 pairs )

 

[PsiStar]

you mean digital

 

[santuitman]

Don't forget to make sure it's disconnected from the street.

 

[Paperdoc]

Well, maybe. First, as others have said, you would HAVE to ensure the wires you use are disconnected from everything else.

The "maybe" part is because of line length and losses. A typical Serial Port on a computer is actually a very specific port type, RS-232. It uses mainly voltage-type signals and high-impedance 5 VDC circuits for communication. Such circuits work well over shorter distances and in the absence of strong external sources of electrical noise. Hence they are well suited to connecting a computer to a printer that is withing 5 to 10 feet. But there is a real limit to how far that connection can extend and still be reliable. For longer distances, one older way was another version of serial data transfer called RS-422 that used low-impedance circuitry and a current-based signal, not voltage-based. It was much better at noise resistance and less likely to suffer from weakened signal over a long line. But that system is almost never found built into a computer mobo or a peripheral device.

There are lots of other ways to connect devices over longer distances, if that is your need. But most of them involve using or installing a different cable. Your question was how NOT to have to do that, and just use what's already there. So, MAYBE it could work.

 

[Colt45]

If it's twisted pair, RS-422 will work. Otherwise you'll need modems.

 

[Modelworks]

From a standard pc serial port, sure. PC serial ports work on a 12V & -12V logic level unlike most of the digital world that is 5 or 3.3Volt. Most of the time that causes problems for people who interface chips because they have to use a level converter to use it safely, but if you want to send it over existing wiring then the 12V output works in your favor

Laptops and USB serial ports are usually 5vdc.