help needed for rs485 !!!!

[michael nikolaou]

Hi to newsgroup

I want to implement an RS485 interface to an microcontroller with the
purpose of creating a network of 10 controllers
located about 200 mt from a pc . Although everything is clear regarding the
interface what is obscure is the protection
needed. I've seen schemes using a 100 ohm resistor between grounds and a 2
zeners series connected clamping at 13 volts
between each data line and ground . Other suggestions are zenistors and
varistors , other suggest optical isolation . Does anybody have experience
to suggest a simple solution (it is a cost sensitive application) to protect
the devices and data lines from surges ??? . I know you can't protect from
all surges but a usual protection is ok.

 

[Jasen Betts]

Hi to newsgroup

I want to implement an RS485 interface to an microcontroller with the
purpose of creating a network of 10 controllers
located about 200 mt from a pc . Although everything is clear regarding the
interface what is obscure is the protection
needed. I've seen schemes using a 100 ohm resistor between grounds and a 2
zeners series connected clamping at 13 volts
between each data line and ground . Other suggestions are zenistors and
varistors , other suggest optical isolation . Does anybody have experience
to suggest a simple solution (it is a cost sensitive application) to protect
the devices and data lines from surges ??? . I know you can't protect from
all surges but a usual protection is ok.

couple the device directly to the rs485 and isolate all the other I/O ?

 

[P.]

Hi to newsgroup

I want to implement an RS485 interface to an microcontroller with the
purpose of creating a network of 10 controllers
located about 200 mt from a pc . Although everything is clear regarding the
interface what is obscure is the protection
needed. I've seen schemes using a 100 ohm resistor between grounds and a 2
zeners series connected clamping at 13 volts
between each data line and ground . Other suggestions are zenistors and
varistors , other suggest optical isolation . Does anybody have experience
to suggest a simple solution (it is a cost sensitive application) to protect
the devices and data lines from surges ??? . I know you can't protect from
all surges but a usual protection is ok.

At such long distances it is much better to use a small dc/dc
converter and optocouplers to isolate the RS485 from your device. And
use a good RS485 driver, there are several.

Whatever clamping you use, you will always have ground loops with
problems if you don't.

P.

 

[Jamie]

Hi to newsgroup

I want to implement an RS485 interface to an microcontroller with the
purpose of creating a network of 10 controllers
located about 200 mt from a pc . Although everything is clear regarding the
interface what is obscure is the protection
needed. I've seen schemes using a 100 ohm resistor between grounds and a 2
zeners series connected clamping at 13 volts
between each data line and ground . Other suggestions are zenistors and
varistors , other suggest optical isolation . Does anybody have experience
to suggest a simple solution (it is a cost sensitive application) to protect
the devices and data lines from surges ??? . I know you can't protect from
all surges but a usual protection is ok.

we use bi-directional TVS diodes across and to ground (3)


http://webpages.charter.net/jamie_5"

 

[michael nikolaou]

Guys

mt stands for meters, thats 0.2 (km or kilometers)

 

[Fred Abse]

mt stands for meters

The usual abbreviation is just "m".