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RS232 Question

Captain Caveman

Active Member
Can anyone point to a tutorial on making custom rs232 cables and how to daisy chain them together? Elk makes it simple with a hub but what about regular cables when not using Elk products?
 

Steve

Senior Member
Welcome to CocoonTech!. May not be exactly what you are looking for but may want to have a look here. It's pretty comprehensive - check links at bottom of that page too.
 

elcano

Active Member
Don't you mean RS485 instead? You dont daisychain RS232.

I did a search about 6 months ago and found very good documents, specially regarding the resistances that must be added to the circuit. I dont remember the recommended resistance values, but I remember the top two restrictions:
  • daisychain directly to the device contacs - Do not use an extension cable to connect from the RS485 cable to the device
  • use resistors ony at the two ends of the daisychain - do not place them at intermediary devices
These two factors are specially important at long runs.

I dont have much time to search the links now, but you can do the search.
 

BraveSirRobbin

Moderator
Captain Caveman said:
Can anyone point to a tutorial on making custom rs232 cables and how to daisy chain them together? Elk makes it simple with a hub but what about regular cables when not using Elk products?
Correct, you can't daisy chain RS-232 but as you suggested, can use an RS-232 distribution box such as the Edgeport (USB to eight serial port adapter).

As far as cabling the RS-232 can you explain more what situations you are using your equipment in (distances, type, etc...). If you are running RS-232 ports for your home and already have Cat5e installed, there are adapters which will let you use this cabling with RJ-45 connections. Of course you have to watch the distances.

Regards,

BSR
 

Captain Caveman

Active Member
Don't you mean RS485 instead? You dont daisychain RS232

Your right, after reading the documentation better I found this to be true.

However, I have been looking at Cortexa's prewire documentation for rs232 thermostats and it states to daisy chain 2 or more together by splicing the cables to each other, then running the cable into a com port.

So now I am looking to see how people are doing this in the field without soldering connections.

Thanks for the quick replies! And yes I have been lurking here for months:)
 

WayneW

Senior Member
RS232 cables are easy to daisy chain, just like AC extension cords. Or you can make your own the desired length.

Thermostats seems to be the one common exception to daisy chaining RS232, but that is because the thermostats were designed to support this feature. I would just use a cat5 run for each thermostat and parallel the connections at the Cortexa unit, rather than a true daisy chain wiring.
 

WayneW

Senior Member
Captain Caveman said:
Do you know the combined maximum distance?
The HAI thermostats work at a blazing 300 baud, so anything under 1,000 - 2,000 feet should work fine. But I haven't personally tested that :)

Here is some info I found in the 'stat documentation:
Intended for connection to personal computers or other systems with RS-232 ports. 4 wires to the thermostat: DTR, RXD, TXD and Ground. All wires are optically isolated in the thermostat. The thermostat transmits with a modified RS-232 transmitter that can be tri-state (high impedance) so that more than one thermostat can be connected in parallel to a single RS-232 port.
 

jbdww

Member
The number of thermostat seems to also make a difference on the distance. HAI says that the max thermostats with out a booster is four. So far we have seen upto six with out the booster, but the six we installed had a total amount of 500 feet of wire.

JBDWW
 
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