Tx Rx how far apart 232

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loup garou

New Member
Does anybody know in a nutshell how far apart I can put two picaxe based circuits using 232 before they will be unable to communicate???

The factors.........size of conductor.....twisted pair.....5V or true 232 with max chip..........or even say 50V modulation in stead of 5V. Will the baud rate have an effect and how........???

My chances of going a mile or two on a private twisted pair....???

??? Modems I guess that would be better??? but why....can we build one with PICAXE???

I hope soon I can help others....but this time I'm back for more help...

Thanks...

John
 
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MPep

Senior Member
Hi John,

If you are using MAX232 type line drivers, I would expect around 15 - 30m. That is what the standard says anyway.
If you are using a direct connection, using 5V logic levels, I would not expect a huge distance at all.

To use twisted pair, look at RS422 or RS485 drivers. Supposedly goes to about 4000feet. Again this is what the standard allows for.

You could also use RF modems, using Yagi antennae (directional!). Another fellow Kiwi (forum member "Manuka") has posted plenty of advise on them. Do a forum search.

MPep
 
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inglewoodpete

Senior Member
Your question is a little vague. RS232 is very limited because of noise getting into the (unbalanced) wires. The slower the data rate, the further you can transmit. You could be lucky and be able to use 1200 bits/second over 100 metres.

For any long distance over wire, I suggest you look at balanced serial transmission (eg RS422). No changes to the PICAXE, just different interface chips and cabling.
 
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moxhamj

New Member
I've gone 200 metres with twisted pair (cat 5) and raw digital from a picaxe (0/5V) at 1200 baud. So RS232 will go further.

It is a matter of slowing down the baud rate till it works.

For a mile, as inglewoodpete says, look at balanced rather than unbalanced. It would be worth going RS422 because you will get a faster baud rate. You can also do some tests in the shed before you roll it out. Get a big box of cat5 and you can usually find the other end of the wire and then try some experiments and see how fast it can go. Then back off the speed a bit to make sure it is reliable.
 
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krypton_john

Senior Member
loup garou said:
Does anybody know in a nutshell how far apart I can put two picaxe based circuits using 232 before they will be unable to communicate???

The factors.........size of conductor.....twisted pair.....5V or true 232 with max chip..........or even say 50V modulation in stead of 5V. Will the baud rate have an effect and how........???

My chances of going a mile or two on a private twisted pair....???

??? Modems I guess that would be better??? but why....can we build one with PICAXE???

I hope soon I can help others....but this time I'm back for more help...

Thanks...

John
Click to expand...
A mile or two of copper cable would be extremely expensive!

You'd be better off setting up a directional RF link - here's what our own 'Manuka' did:
http://www.engadget.com/2005/03/22/wifi-wok-and-the-chinese-cookware-2-4ghz-repeaters/
 
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leftyretro

New Member
I can vouch for RS422 type driver/receiver chips. We used them in a refinery and could move 9600 baud data for a good mile or more. Need good quality twisted pair wire with shielding and proper termination resistors per driver/receiver data sheets. Works good and wire costs are the major expense. Wireless is more cost effective these days but at the refinery there was just too much concern over reliability when used for process control applications. We did use some wireless for remote non critical measurement of wind speed and direction, etc.

Lefty
 
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BeanieBots

Moderator
You could also consider a few simple repeater/buffer chips along the way.
Would require one extra core but very easy to do.
 
hippy

hippy

Ex-Staff (retired)
I've sent DMX-512 ( 250,000 baud ) using RS422/RS485 ( cannot recall which ) through 1km of coiled mains cable during testing without problems, with an arc welder running to try and induce interference.
 
hippy

hippy

Ex-Staff (retired)
Some more definitive statements on cable length ...

Cable length is one of the most discussed items in RS232 world. The standard has a clear answer, the maximum cable length is 50 feet, or the cable length equal to a capacitance of 2500 pF. The latter rule is often forgotten. This means that using a cable with low capacitance allows you to span longer distances without going beyond the limitations of the standard. If for example UTP CAT-5 cable is used with a typical capacitance of 17 pF/ft, the maximum allowed cable length is 147 feet.

The cable length mentioned in the standard allows maximum communication speed to occur. If speed is reduced by a factor 2 or 4, the maximum length increases dramatically. Texas Instruments has done some practical experiments years ago at different baud rates to test the maximum allowed cable lengths.

19200 baud : 50 feet
9600 baud : 500 feet
4800 baud : 1000 feet
2400 baud : 3000 feet

So, taking TI's figures and geting an extension by using Cat5, at 2400 baud, it would seem that near 10,000 feet is possible, even more with balanced line drivers, and in practice even greater distances may work.

http://www.lammertbies.nl/comm/info/RS-232_specs.html
 
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loup garou

New Member
Thank you once again......

It could take a while but I am putting something together bit by bit.

Who knows I may even be able to try it on a twisted pair one day.

I'd love to try something over a mile....

Best regards

John
 
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