Serial Cable Length

[apostolakisl]

I need to put the PLM in a bit of an open and central location to catch all the thermostats radio signal at my church.  We only have the thermostats so there is no PLC or repeating going on here.  I've got a great spot with robust communication and now need to run the wire back to the ISY.  Currently I've got the ISY next to the PLM as a temporary setup, but I would prefer ISY to be in the network rack with everything else.  Was wondering what sort of experience people had with the length of the cable.  I tried a 30 foot  cat5 I had sitting around and it failed.

 

I have high end cat6 23 gauge in a box and plan to make a custom cable, but don't want to waste my time and effort putting ends on the wire to just find out it is too long.  I could perhaps make do with 10 feet, but it would be a much cleaner run with about 20 feet.

[KeviNH]

Interesting that your pre-made Cat5 cable failed to work.  Maybe it is faulty, tried a cable tester on it?

 

The PLM uses 3 wires, a different subset of the available lines compared to Ethernet, so a cable could work for 100Mbit networking yet fail when used for PLM.  IIRC, the serial communication uses pins 1,7,8 at 19,200 bits/second (baud); slow enough that it should be generally forgiving of the usual issues that might come with long cable runs.

 

My ISY994 is 30 feet from my PLM, extended using standard Cat5e off a bulk spool, via patch panels.   See this old thread:

http://forum.universal-devices.com/topic/18274-maximum-distance-between-isy-and-plm/?hl=serial&do=findComment&comment=168187

[apostolakisl]

Interesting that your existing Cat5 cable failed to work.  Maybe it is faulty, tried a cable tester on it?

 

My ISY994 is +25 feet from my PLM, extended using standard blue Cat5e cable via patch panels.

 

The cable works for internet.  Currently the ISY is using that cable to connect to the network (successfully).  ISY I think is only 100mb, but I am pretty sure I have used that same cable for gigabit . . . meaning that all 4 pairs must work.   It could be that the wire is even longer than 30 feet, I haven't measured it.

 

However, based on your comment, I now feel pretty good about making a custom cat6 wire that is 20 feet.

[Brian H]

Only three wires are used for the serial signals.

No handshake connections on the Serial Port connector of the PLM.

 

From the quick guide and Modem Developers Guide.

1 RS232  Out to PC Pin 2 (RX)

7 Common

8 RS232 In from PC Pin 3 (TX)

 

Note Pin 3 is a TTL Level Output (from PLM)

        Pin 6 is a TTL Level Input. (to PLM)

Not too sure how well they are protected from noise.

[jtara92101]

Comparing Ethernet to serial is not comparing apples to apples.

 

Ethernet over Cat-n uses a fairly sophisticated signaling scheme. And is using multiple pairs. 

 

Serial RS-232 uses a very unsophisticated signaling scheme - simple mark/space.  Above a certain voltage level is a 1. Below a certain voltage level is a 0. (There is some hysteresis.)

 

The PLM has both RS-232 and TTL (5V) signal levels available, not sure which the ISY uses. 

 

Either way, RS-232 goes to pot when the signal edges get rounded enough to make bit recognition unreliable.

 

RS-232 maximum length is speced at 50 feet for 19,200bps, OR a maximum measured capacitance of 2500pf.

 

    https://www.lammertbies.nl/comm/info/RS-232_specs.html

 

I believe UDI specifies 10 feet. And, even so, urges you to "keep it short".

 

Have you considered an extension cord for the power?

 

Or, buy a pair of RS-232-over CAT5 extenders. You'd use the same CAT5 cable. It would be a bit goofy, you'd need to rig an adapter from the CAT5 connectors on the ISY and PLM to the standard RS-232 D-sub connectors on the extender.

[KeviNH]

When unsuccessful, debugging serial can be non-trivial, especially without access to a oscilloscope, etc..   If the problem is induced noise,a shield cable might help but if the problem is capacitance, switching to a shielded cable will make it worse.

 

Ultimately, if you have the ISY next to the PLM as a temporary setup and that is working, you might want to just make that permanent.

 

Or, buy a pair of RS-232-over CAT5 extenders. You'd use the same CAT5 cable. It would be a bit goofy, you'd need to rig an adapter from the CAT5 connectors on the ISY and PLM to the standard RS-232 D-sub connectors on the extender.

 

I suggested the extender solution as a last-ditch option in the earlier thread, but those active converters are not cheap, and are usually only necessary for extreme distances (in the hundreds to thousands of feet), and/or at much higher baud rates. 

 

I've had no problems with regular Cat-5e at 30', other users here have gone to +60' successfully with just a long piece of Cat6 cable.

[larryllix]

The connectors on one end may be the wrong polarity style (A or . Most Ethernet will work with either cable style but serial won't.

[apostolakisl]

The connectors on one end may be the wrong polarity style (A or . Most Ethernet will work with either cable style but serial won't.

 

No, I made this wire.  It is b at both ends.  But I made it like 10 years ago.  It is what was the standard cat5e wire at the time as far as wire quality, but the cat6 heavier gauge wire now is a lot better.  

[giesen]

Would just buying a plug-in dual-band module be an acceptable solution? You could put it near the thermostats, and as long as it's on the same electrical phase as the PLM is, should extend your reach wherever you need it (within reason)

 

Sent from my SM-N910W8 using Tapatalk

[larryllix]

No, I made this wire.  It is b at both ends.  But I made it like 10 years ago.  It is what was the standard cat5e wire at the time as far as wire quality, but the cat6 heavier gauge wire now is a lot better.  

I think B on both ends would twist the signals. To be straight through IIRC it takes B on one end and A on the other.

ISY Tx = PLM Rx

ISY Rx = PLM Tx

 

B to B may connect Tx to Tx and Rx to Rx

 

 

Since serial ports don't usually auto change connection function, like many Ethernet ports now,  it probably shouldn't work.

[KeviNH]

I think B on both ends would twist the signals. To be straight through IIRC it takes B on one end and A on the other.

ISY Tx = PLM Rx

ISY Rx = PLM Tx

 

B to B may connect Tx to Tx and Rx to Rx

Ethernet with A on one end and B on the other is called a crossover cable.

 

A patch cable is wired with either A on both ends, or B on both ends.   The "normal" use of an Ethernet cable is to connect a computer to a switch, in which case the transmit/receive pins are already different on the switch than on the computer (though modern Auto MDI-X takes care of this now).

A third type of cable are the special flat RJ-45 cables (usually pale blue, sometimes black) you see for serial console on networking gear, popularized by Cisco.  These are usually "roll" cables and should only be used for Cisco-style serial connections, never for networking.

 

 

[jtara92101]

We should all hang our heads in shame! 

 

Except giesen:

 

 

Would just buying a plug-in dual-band module be an acceptable solution? 

 

Use one or more Range Extenders:

 

   http://www.insteon.com/range-extender/

 

Or else, if you might find some use for the additional functionality, any dual-band Insteon device(s). Some have better range than others, though - search the forum.

 

Apparently, the dual on-off outlet has particularly good range. I think better than the PLM itself or even the range extenders. It has the latest version of the Insteon RF circuitry, and they claim greater range. More Insteon products will probably be released with the greater range. Search the forum - it's been discussed here.

 

I would not assume that it will be possible to find a single central location that will reliably reach all of your thermostats. That's the duct-tape and prayer solution.

 

Please verify that your thermostats Use Insteon RF signaling, not Z-wave. I presume that is the case, since you have a PLM and don't have any other Insteon devices other than the thermostats.

[apostolakisl]

I have it all working great as is. I don't need any range extender or repeater. I just want to put the plm about 15 ft away from isy for aesthetics. When I get the time, I'm going to just make a 15 ft cat 6 and see how it goes. Mind you, this is 3 phase, so any repeaters would need to be on the same phase or else I need multiples and then I'll have these boxes plugged I random locations in a public building.

[ELA]

Hello Apostolakisl,

   Since you want to stick with extending the RS232 you might have better results by making your Cat 5 or 6 cable in a more custom fashion.

   Those cables are really intended for ethernet type differential communications.  Rs232 is single ended and to take better advantage of the twisted pairs I would recommend only connecting the three  lines needed 1,7,8 as Brian detailed.   Use two wire pairs and put tx and gnd on one pair and rx and ground on the other pair.   This would of course require a pigtail from pin 7 to the two gnds (commons).

 

here is  a link that talks about extending RS232  :  http://www.marcspages.co.uk/tech/long232.htm

[Brian H]

Another reason to use only the three serial signals.

The TTL signals are not very well isolated from the outside world in a PLM.

The logic level signal to the RS232 IC transmit input is also brought directly out of pin 2 of the connector.
No buffering at all. Accidentally ground it and you effectively kill the transmit data.

The TTL input on pin 6 of the connector and the logic level receive signal from the RS232 IC are isolated from
each other by two 1N4148 diodes. Into the main board. If you accidentally ground pin 6. The receive data is effectively killed.

[larryllix]

Another reason to use only the three serial signals.

 

The TTL signals are not very well isolated from the outside world in a PLM.

 

The logic level signal to the RS232 IC transmit input is also brought directly out of pin 2 of the connector.

No buffering at all. Accidentally ground it and you effectively kill the transmit data.

 

The TTL input on pin 6 of the connector and the logic level receive signal from the RS232 IC are isolated from

each other by two 1N4148 diodes. Into the main board. If you accidentally ground pin 6. The receive data is effectively killed.

Are the signal levels RS232 or logic levels? That would determine the capability of the signals.

 

We know you can't connect Tx to Tx so something has to switch the connections. This means a straight through cable isn't going to work the same way as a real RS232 cable always needs pins 2 and 3 cross wired. (Tx to Rx, both directions)

 

Sent from a tiny keyboard. Response may be brief.

[Brian H]

RS232. Older PLM's have a ST232 chip for the RS232 signals. It also has the TTL logic level I/O on different pins but it doesn't look like they thought much of protecting the TTL signals in the design.

The latest V2.3 has changed the chip to a TI MAX232E that meets the IEC61000-4-2 ESD protection requirements.

The last post in the long PLM repair thread. I posted what I found in the V2.3 PLM's

 

I believe the ISY994i takes into account the serial signal pins needs. As all of  mine came with a standard 3' patch cable. No fancy  cable pinout's.

 

If you are interested in the schematic of the Serial Board it is in the developers guide.

http://cache.insteon.com/developer/developer-guide-022009-en.pdf

 

The guide  is for the original 2412S 417 Link Database.

U3 is a 24LC128 in the large Link Database 2412S

U3 is a 24FC64 in a 2413S and F1 is not installed. To remove the unregulated 12 volt from pin 2 of the serial connector.

[ELA]

Brian,

  I agree and it is the reason that I said only three signal lines should be  used.

Capacitive coupling occurs between wires inside of the cable. This is often referred to as crosstalk.

The longer the cable the worse the crosstalk. Why you do not want anything but a common in the same twisted pair with an Tx or Rx signal.

The TTL level signals should not be included in any longer length cables.

[mwester]

@larrylix -- don't get hung up on cross-over cables for RS232 serial stuff... that standard defines a DTE (Data Terminal Equipment) end and a DCE (Data Communications Equipment) end.  The TX and RX pins are swapped between the two, so a straight-through cable worked just fine.  The implementation using the RJ45s on the PLM and ISY follows the same idea -- the TX and RX pins are swapped so a straight-through cable works just fine there too.

[apostolakisl]

Hello Apostolakisl,

   Since you want to stick with extending the RS232 you might have better results by making your Cat 5 or 6 cable in a more custom fashion.

   Those cables are really intended for ethernet type differential communications.  Rs232 is single ended and to take better advantage of the twisted pairs I would recommend only connecting the three  lines needed 1,7,8 as Brian detailed.   Use two wire pairs and put tx and gnd on one pair and rx and ground on the other pair.   This would of course require a pigtail from pin 7 to the two gnds (commons).

 

here is  a link that talks about extending RS232  :  http://www.marcspages.co.uk/tech/long232.htm

Thanks.  I'll play around with it and let you know what happens.

[larryllix]

@larrylix -- don't get hung up on cross-over cables for RS232 serial stuff... that standard defines a DTE (Data Terminal Equipment) end and a DCE (Data Communications Equipment) end.  The TX and RX pins are swapped between the two, so a straight-through cable worked just fine.  The implementation using the RJ45s on the PLM and ISY follows the same idea -- the TX and RX pins are swapped so a straight-through cable works just fine there too.

So if I read you correctly, the hardware at each end ie. PLM / ISY is wired differently to accomodate a cable, with identical pin numbers wired together. Is that not what you are calling "straight-through"?

 

This is the way the original Ethernet hubs and switches were wired, but the cables would never be able to connect two hubs together, or two computers together. That was the "other" cable required with Tx wired to Rx. It was a mess for a while, and I think this has been since straightened out, similar to RS232 cables. Tx and Rx are always crossed or all connectors have auto crossover capabilities.

 

As much as I have wired a few thousand RJ45 connectors, by hand for a fibre WAN system, I really have never studied the connection purposes of the pinouts.

[KeviNH]

So if I read you correctly, the hardware at each end ie. PLM / ISY is wired differently to accomodate a cable, with identical pin numbers wired together. Is that not what you are calling "straight-through"?

 

This is the way the original Ethernet hubs and switches were wired, but the cables would never be able to connect two hubs together, or two computers together. That was the "other" cable required with Tx wired to Rx. It was a mess for a while, and I think this has been since straightened out, similar to RS232 cables. Tx and Rx are always crossed or all connectors have auto crossover capabilities.

 

As much as I have wired a few thousand RJ45 connectors, by hand for a fibre WAN system, I really have never studied the connection purposes of the pinouts.

 

Ethernet cables and RS-232 cables are by default wired straight-through, that is the standard cable type.  When a crossover or "null modem" cable is needed, that is a special exception, and is usually labeled as such, or for Ethernet, might be colored red or yellow.

 

Many modern Ethernet devices have automatic medium-dependent interface crossover (auto-MDIX) functionality in the device (not in the cable), that is the auto crossover.    But the cables are not special, the port (driver chip) inside the computer or switch is.

[builderb]

First time I needed to make a cable, I bought a crappy combo termination kit with a very cheap crimp tool. Tons of failed cables, and much frustration. I have since bought a much nicer crimp tool, and have had zero failures since.

 

My current installation has a fairly short custom CAT 6 cable of about 36", but I have previously had it as far as 24' (of cable) away from my ISY with no ill effects.

[apostolakisl]

I went ahead and made a 20 foot cat6 cable to use as serial between the plm and isy.  It appears to be working just fine.