help needed:how can i get power from rs232 data line?

get power rs232

Hi,friends:
I am working on a rs232 repeater and got some problems...

1)How can i extend the rs232 distance up to 1.0 miles above?

2)I want to power the repeater from the data line,not the rts pin or dts.but,how should i do??

Can someone show me an example schematic?
Thx....thx

get power from rs232

Hi,
I think you will have trouble over that distance using RS232 and as there is no other voltages normally present on the connector other than the signals so you will have trouble driving your remote repeaters.

I would suggest that you use the RS485 standard, this will easily carry the distance that you want using a two core screened twisted pair cable without a repeater. You can either buy USB to RS485 converters for each end of the link or design and build your own, they are not too difficult to make using the FTDI chips or modules. The USB ports have at least 0.5A available at 5V to power them. The signal format is the same over RS485 as RS232 but the line voltage levels are lower. The drivers for these devices map to virtual COM ports so communicating with them is easy.

Hope this helps
Regards,
Bob.

hi,thanks Drbob13,
The repeater which can extend the distance of RS232 displayed on "http://www.rs232-converters.com/opto-isolated_rs232_repeater.htm".I want to complete a repeater like it.
The trouble is get power from data line and extend the distance....
At least,mine could power from data line.
so,anybody help me?

Hi,
In such applications, if the RS232 baudrate is not very high, you can avoid repeaters using FSK modem ICs. Depending on signal for power is always a tricky design.
Regards,
Laktronics

I think rs232 was meant to go to a computer to a printer and that was about it. I think it is meant to go 15 feet. It does not even use differential signalling. Anyway, capacitance rears it's ugly head over distances and impedance matching becomes all-important. The problem you bring up is not trivial and is actually a huge part of communications engineering. You need to look atconverting it to 485 as mentioned, and using twisted pair shielded wiring and test the signal. Once the voltage drops a certain amount you would need to amplify it back to original levels. This could be every 100 feet, or every 500 feet, I don't really know. Also, you would want to filter it. And if you are thinking of doing this in an industrial environment with motors and whatnot, forget it. Again, it was designed for quiet office environments. Take a look at a pic microcontrollers with CAN, it has registers for testing phase and noise jitter and all kinds of things to do with noise. And it still is not meant to go a mile. There are reasons why nobody looked at trying to transfer data over any distance with rs-232. They simply went to better technologies.