RS232 Cable wiring.

Tharon

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I'm new to the world of RS232 Cable wiring, and am looking for some confirmation on how I'm doing this.

I'm trying to make a communication cable to go from a Fagor DRO to a PC. The diagram (Page 3 of the manual, DRO to 9pin PC) shows the PC end has two jumpers (4-6 and 7-8). Are these physical jumpers on the inside of the cable? I don't want to break my serial port on my laptop if I screw this up :)

BTW, this is a project I took from someone else, and they couldn't get their cable to work. I opened up their contectors and noticed no jumpers, and am wondering if that's why they couldn't get it to work.
 
RS232 (Recommended standard ?!?)

PC Fagor
rx tx
tx rx
gnd gnd
rts - cts jumper (7-8) (PC side)

Check connector on PC. Sub D9 and Sub D25 has for pin 2 and pin 3 a different lay out. Probably 9 pin. (2<->3, (3<->2),(5<->5)
Be carefull with rs232. Do not connect it wrong.
Good luck.
 
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Thanks for your help.

I got it to work and didn't break anything, that's always good. I got worried when you said "Be carefull with rs232. Do not connect it wrong."

Is is possible to ruin a port if you wire a cable wrong?
 
When you mix up pins on RS232 then you got trouble. Normally the chip controlling the port is defective.
With RS485 a-b wiring is no problem when you mix it up. Well it doen't work but no hardware problems.

Regards,
 
I know nothing about your specific equipment, so these comments are for rs-232 signals in general. Pins 4-6 and and 7-8 were probably DTR/DSR and CTS/RTS. Those are handshaking lines that are rarely needed by equipment these days. Most computers can still handle them though, you just go into the driver and enable handshaking. So, a lot of 'standard' pinouts just have you install those jumpers to manually bypass any handshaking. The idea is that as soon as the device sets the line high to request data (or to request permission to send it) it responds to itself to go ahead.

Anyway, no harm in connecting those even if they are not technically needed. There's also usually no harm in just connecting them through to the other device, its just more complicated. But to be clear, most of the time you only need Tx, Rx, and Gnd. When I'm developing a new cable for some odd combination of equipment, I generally try to make it work with just those 3 lines.

I'm not sure what s7xp was referring to. The only time I've seen it cause problems when pins were mixed up was if a particular device was sending out voltage on one pin to power up another device. Modicon PLCs put out some constant voltage on pin 1, for example. But, when just dealing with standard pins, there should be no problem. The voltage levels on all of them should be the same, around +-5v. Sure, the communications wont work, but I can't see how it would fry the com port. I have had pins crossed every which way a number of times, looking for the right combination, and I've never seen that happen. Not saying that scenario isn't possible, but its probably only an issue with specific equipment. I'd be interested in hearing what that specific equipment is. (maybe the Fagor DRO you were asking about has this issue).


-jeff
 
Hakutsuru said:
... The voltage levels on all of them should be the same, around +-5v...-jeff
+-12v is the standard, and what you would expect from a desktop or PLC. Many laptops cheat with 5 volts. I agree with everything else.
 
keithkyll said:
+-12v is the standard, and what you would expect from a desktop or PLC. Many laptops cheat with 5 volts. I agree with everything else.

Actually the signal could be anywhere from -25 to +25 with the transition between -3 and +3 being a no transition state. Desktop power supplies offfe 3v, +/-5, and +/- 12.

This will offer a lot of info on R232, in some cases all of the wires may be necessary. http://www.camiresearch.com/Data_Com_Basics/RS232_standard.html
 
Any advice for a person with very poor soldering skills? I finished the connections but they look far from pretty (but they do function, and are fairly sturdy).

They probably don't make screw or compression terminal models, do they?
 
May be late but if there is a next time use heat shrink, place it on the wire and when finished with all then shrink them over the soldered connetions. When soldering use a little flux even with flux core solder, allows the solder to run smoother. I think .032" diameter is best for stuff like this .Also when working with small connectors like this use a soldering iron with a pointed tip and low wattage settingm or a 25w pencil tip.
As long as there is no chance of the wires contacting each other do worry too much, any balls of solder melt off or at least where it is unlikely to touch something.

It also help to have helping hands: http://www.radioshack.com/product/index.jsp?productId=2104639&cp=2032058.2032236.2032314&pg=2&parentPage=family

BTW, yes they make terminal connector DB9 etc, here is an example: http://www.rs-485.com/daqaddonw.asp?record=43
 
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Another tip on soldering if it takes longer than 1 minute to heat up the pin from a communication shell using 24 awg wire you are probably overheating the biggest trick in soldering is proper cleaning. If the solder joint looks like a bubble you are too cold. If it runs all over the place then your too hot.
 
Tharon said:
Any advice for a person with very poor soldering skills? I finished the connections but they look far from pretty (but they do function, and are fairly sturdy).

They probably don't make screw or compression terminal models, do they?

I think I saw a screw one once. But I prefer to use crimp and poke connectors. On top of being much easier, they're supposed to have better vibration immunity. I also often use the the 9-pin(or 25 pin) to RJ45 converters. You know, the ones that are customizeable. I wish I could remember the proper name for them. They look bad, but once you get the hang of them they are quick and easy and your cable length is instantly adjustable, just throw in any length ethernet cable you can find. Plus, they don't take up as much room in your laptop case.

As for soldering tips, I agree with everything that was said, but I would add 1 more thing. Tin the wire and the cup first. Then when you go to make the connection, put the solder away. Biggest mistake I used to make was trying to apply that solder like glue and winding up with a big glob. Doing it that way also means you now only need 3 hands instead of 4, so its got that going for it. Oh yeah, and you know you're technically not supposed to touch the solder to the iron, right? You're supposed to heat up the thing you are connecting enough for it to melt the solder. In practice (see my sig) it doesn't work exactly like that when building cables, but if you keep it in mind it might help you make better connections.


-jeff
 
problem with the alternative connectors mentioned that I've noticed is that they don't handle high washdown areas as well as the solder joints. Good point on tinning I forgot to mention that step
 

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