RJ-45 for instrument interface

Started by Steve Wilson March 12, 2018
Den tirsdag den 13. marts 2018 kl. 16.48.17 UTC+1 skrev John Larkin:
> On Tue, 13 Mar 2018 03:52:05 -0700 (PDT), mpm <mpmillard@aol.com> > wrote: > > >On Tuesday, March 13, 2018 at 6:48:23 AM UTC-4, mpm wrote: > > > >BTW: A little off topic maybe...? > > > >It too bad that IrDA hasn't really seemed to garner wide-spread use as a
short-range bi-directional data interface.
> > > >Even my cell phone, (Samsung Galaxy S5) only offers one-way IR, and I'm not even
sure if that's IrDA.
> > > >Seems like a dirt-cheap way to get something done. > > It would be nice if everything were wireless. We wouldn't need a > tangle of hubs and cables. >
ESP8266, and you can have WiFi on anything with a serial port a module with flash and antenna is less that an FTDI chip at digikey
On Tuesday, March 13, 2018 at 8:48:17 AM UTC-7, John Larkin wrote:


> It would be nice if everything were wireless. We wouldn't need a > tangle of hubs and cables.
Oooh, ick. If everything were wireless, the next interfering signal I'd have to track down could be... anything, anywhere To get rid of a tangle, consider instead a multiplicity of IRDA-equipped gizmos, all with eyepatches.
On 13/03/2018 00:17, krw@notreal.com wrote:
> On Mon, 12 Mar 2018 20:52:29 +0000, Mike Perkins <spam@spam.com> > wrote: > >> On 12/03/2018 15:26, Phil Hobbs wrote: >>> On 03/12/2018 10:59 AM, John Larkin wrote: >>>> On Mon, 12 Mar 2018 12:56:00 GMT, Steve Wilson <no@spam.com> wrote: >>>> >>>>> Since modern computers have no serial or parallel interfaces, the old GPIB >>>>> and RS-232 interfaces are obsolete. There have been discussions about other >>>>> interfaces such as HDMI, but the connector is a bit large. >>>>> >>>>> Consider a setup with a controller connected to the LAN. It may need to >>>>> connect to several or dozens of separate boxes for measurement and control >>>>> functions. Is it a good idea to use RJ-45 for these interfaces also? >>>>> >>>>> The connectors are small, locking, bidirectional, high speed, cable length >>>>> up to 300m, very inexpensive, readily available, and have sufficient pins >>>>> for most needs. >>>>> >>>>> https://en.wikipedia.org/wiki/Modular_connector >>>>> >>>>> The RJ-45 pinouts are well defined and can probably be used as is. One >>>>> issue is with POE, power over ethernet. The voltage applied can be 48V, >>>>> which could destroy most electronics if not controlled. The spec says it >>>>> can only be applied if there is a proper handshake between source and load, >>>>> but that could go awry. >>>>> >>>>> The cables can be double-shielded and come in various lengths and colors. >>>>> Here are some examples: >>>>> >>>>> "When a regular shield is not enough, L-com's exclusive double-shielded >>>>> SF/UTP patch cables are ideal. Category 6 tested, these cables use L-com's >>>>> superior shielding to drastically reduce EMI/RFI interference using a 100% >>>>> foil plus a 65% braid shield. The Low Smoke Zero Halogen jacket allows this >>>>> industrial patch cable to meet today's environmental and safety >>>>> requirements. With 26 AWG stranded conductors, this cable is flexible and >>>>> easy to install even in tight spaces. We stock in full lengths up to 100 >>>>> feet so that equipment runs can be pulled directly and simply plugged into >>>>> either end." >>>>> >>>>> https://tinyurl.com/pf3p4xg >>>>> >>>>> "Tera Grand - Premium CAT7 Double Shielded 10 Gigabit 600MHz Ethernet Patch >>>>> Cable for Modem Router LAN Network - Built with Gold Plated & Shielded RJ45 >>>>> Connectors, 3 Feet White" >>>>> >>>>> https://tinyurl.com/ya472pcr >>>>> >>>>> "Cat 7 Shielded Ethernet Cable 5 ft 6 Pack ( Highest Speed Cable ) Cat7 >>>>> Flat Ethernet Patch Cables - Internet Cable for Modem, Router, LAN, >>>>> Computer - Compatible with Cat 5e, Cat 6 Network" >>>>> >>>>> https://tinyurl.com/y7sfsx9w >>>>> >>>>> What are your thoughts? >>>> >>>> Putting an FTDI USB-to-serial chip on your board is the easiest way to >>>> interface a small instrument. Your internal uP sees a serial >>>> interface, and the control computer sees a usb-serial chip. Most OS's >>>> are familiar with the FTDI chip. >>>> >>>> It's equivalent to burying a USB-serial dongle inside your gadget. Use >>>> USB hubs and cables. >>>> >>>> If you need to go long distances, go Ethernet but that's a bit more >>>> work. >>> >>> We use FTDIs too. The problem in Windows is that you don't know how the >>> ports are going to enumerate, so it's hard to use multiple instruments. >>> >>> The Prologix GPIB-Ethernet can run a few GPIB instruments, but not a >>> whole rack-full. >> >> FTDI have a utility that can name a FTDI chip, such that when it >> enumerates it has a com port and a name. >> >> You then need an application that searches for the name which is >> independent of com port number. > > Nice. I'll have to look for those. I've been using a MicroChip part > (I get them free) but that would make me switch. How do you program > the name?
I use a bespoke application written by someone else, however this page should help: http://www.ftdichip.com/Support/Utilities.htm#FT_PROG -- Mike Perkins Video Solutions Ltd www.videosolutions.ltd.uk
On Tue, 13 Mar 2018 12:46:29 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

>On Tuesday, March 13, 2018 at 8:48:17 AM UTC-7, John Larkin wrote: > > >> It would be nice if everything were wireless. We wouldn't need a >> tangle of hubs and cables. > >Oooh, ick. If everything were wireless, the next interfering signal I'd >have to track down could be... anything, anywhere > >To get rid of a tangle, consider instead a multiplicity of >IRDA-equipped gizmos, all with eyepatches.
Instead of hubs, we'd use mirrors. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Tue, 13 Mar 2018 19:52:04 +0000, Mike Perkins <spam@spam.com>
wrote:

>On 13/03/2018 00:17, krw@notreal.com wrote: >> On Mon, 12 Mar 2018 20:52:29 +0000, Mike Perkins <spam@spam.com> >> wrote: >> >>> On 12/03/2018 15:26, Phil Hobbs wrote: >>>> On 03/12/2018 10:59 AM, John Larkin wrote: >>>>> On Mon, 12 Mar 2018 12:56:00 GMT, Steve Wilson <no@spam.com> wrote: >>>>> >>>>>> Since modern computers have no serial or parallel interfaces, the old GPIB >>>>>> and RS-232 interfaces are obsolete. There have been discussions about other >>>>>> interfaces such as HDMI, but the connector is a bit large. >>>>>> >>>>>> Consider a setup with a controller connected to the LAN. It may need to >>>>>> connect to several or dozens of separate boxes for measurement and control >>>>>> functions. Is it a good idea to use RJ-45 for these interfaces also? >>>>>> >>>>>> The connectors are small, locking, bidirectional, high speed, cable length >>>>>> up to 300m, very inexpensive, readily available, and have sufficient pins >>>>>> for most needs. >>>>>> >>>>>> https://en.wikipedia.org/wiki/Modular_connector >>>>>> >>>>>> The RJ-45 pinouts are well defined and can probably be used as is. One >>>>>> issue is with POE, power over ethernet. The voltage applied can be 48V, >>>>>> which could destroy most electronics if not controlled. The spec says it >>>>>> can only be applied if there is a proper handshake between source and load, >>>>>> but that could go awry. >>>>>> >>>>>> The cables can be double-shielded and come in various lengths and colors. >>>>>> Here are some examples: >>>>>> >>>>>> "When a regular shield is not enough, L-com's exclusive double-shielded >>>>>> SF/UTP patch cables are ideal. Category 6 tested, these cables use L-com's >>>>>> superior shielding to drastically reduce EMI/RFI interference using a 100% >>>>>> foil plus a 65% braid shield. The Low Smoke Zero Halogen jacket allows this >>>>>> industrial patch cable to meet today's environmental and safety >>>>>> requirements. With 26 AWG stranded conductors, this cable is flexible and >>>>>> easy to install even in tight spaces. We stock in full lengths up to 100 >>>>>> feet so that equipment runs can be pulled directly and simply plugged into >>>>>> either end." >>>>>> >>>>>> https://tinyurl.com/pf3p4xg >>>>>> >>>>>> "Tera Grand - Premium CAT7 Double Shielded 10 Gigabit 600MHz Ethernet Patch >>>>>> Cable for Modem Router LAN Network - Built with Gold Plated & Shielded RJ45 >>>>>> Connectors, 3 Feet White" >>>>>> >>>>>> https://tinyurl.com/ya472pcr >>>>>> >>>>>> "Cat 7 Shielded Ethernet Cable 5 ft 6 Pack ( Highest Speed Cable ) Cat7 >>>>>> Flat Ethernet Patch Cables - Internet Cable for Modem, Router, LAN, >>>>>> Computer - Compatible with Cat 5e, Cat 6 Network" >>>>>> >>>>>> https://tinyurl.com/y7sfsx9w >>>>>> >>>>>> What are your thoughts? >>>>> >>>>> Putting an FTDI USB-to-serial chip on your board is the easiest way to >>>>> interface a small instrument. Your internal uP sees a serial >>>>> interface, and the control computer sees a usb-serial chip. Most OS's >>>>> are familiar with the FTDI chip. >>>>> >>>>> It's equivalent to burying a USB-serial dongle inside your gadget. Use >>>>> USB hubs and cables. >>>>> >>>>> If you need to go long distances, go Ethernet but that's a bit more >>>>> work. >>>> >>>> We use FTDIs too. The problem in Windows is that you don't know how the >>>> ports are going to enumerate, so it's hard to use multiple instruments. >>>> >>>> The Prologix GPIB-Ethernet can run a few GPIB instruments, but not a >>>> whole rack-full. >>> >>> FTDI have a utility that can name a FTDI chip, such that when it >>> enumerates it has a com port and a name. >>> >>> You then need an application that searches for the name which is >>> independent of com port number. >> >> Nice. I'll have to look for those. I've been using a MicroChip part >> (I get them free) but that would make me switch. How do you program >> the name? > >I use a bespoke application written by someone else, however this page >should help: > http://www.ftdichip.com/Support/Utilities.htm#FT_PROG
Nice. Thank you.
On Tue, 13 Mar 2018 02:45:04 GMT, Steve Wilson <no@spam.com> wrote:

>I'm just >trying to protect agains accidentally plugging into an existing POE jack. >If there is 48V in the jack, my regulator would have to survive while >dissipating extra heat.
I doubt if there is a 48VDC passive PoE system in the wild. It's possible, but I have yet to see one. Mostly, I see 5V, 12V, and 24V passive PoE systems. Mostly, they go through adapters like this: <http://www.dx.com/p/5v-rj45-female-to-rj45-male-dc-male-dc-female-power-over-ethernet-poe-adapter-black-208704> So, the most you'll need to protect against is 24VDC.
>I'll add a shutdown circuit to disable the >connection if the voltage exceeds +5V or so. I know you say it should not >be a problem since the handshake is so complex, but things do go awry.
Not exactly. I said with 802.3af and similar active PoE systems, you should not have a problem. It's the passive power sources, that have no smarts and often no protection, that is likely to cause problems.
>I'd >hate to have to argue with a customer that my equipment failed because >there was excessive voltage on the plug:)
You will anyway. There is wide range of contrivances that use RJ45 connectors that might do damage. Short list: Motorola, Kenwood, Yeasu, and Icom 2-way radio mic connectors. Video terminals and teletype machines. RJ45 RS232 devices such as terminal servers. Light pens. Many telephone systems (all with PoE). Whatever else I forgot. It will be difficult to protect against all these. Besides users that cram a USB connector into the ethernet jack, there's also the problem of the gold wire connections being mangled inside the RJ45 jack. Three ways that I know of to do that: 1. Cram something into the RJ45 that doesn't belong and wiggle. 2. Use an RJ11 or RJ14 plug in an RJ45 jack. (More on this below) 3. Cram an RJ45 plug into the jack which was NOT crimped. The result of all of these is to have the gold wires in the jack move over a notch, thus shorting two adjacent pins together. If the adjacent pin carries power, it might blow something up. Internally, the jack has a plastic "comb" that acts as a separator and spreader for the gold wires. It doesn't take much to lift a gold wire from the comb, move it to the adjacent slot, and produce a short. The mangled RJ45 has become common enough that designers are defending themselves by making the connector an easily replaceable part. Most common is using a dual RJ45 "barrel" connector. Something like this: <https://www.amazon.com/Waterproof-CAT5e-RJ45-Feed-Thru-Coupler/dp/B00CULLAWE> If the connector gets mangled, just unplug, remove and replace. Anyway, good luck. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Jeff Liebermann <jeffl@cruzio.com> wrote:

> On Tue, 13 Mar 2018 02:45:04 GMT, Steve Wilson <no@spam.com> wrote:
>>I'm just >>trying to protect agains accidentally plugging into an existing POE >>jack. If there is 48V in the jack, my regulator would have to survive >>while dissipating extra heat.
> I doubt if there is a 48VDC passive PoE system in the wild. It's > possible, but I have yet to see one. Mostly, I see 5V, 12V, and 24V > passive PoE systems. Mostly, they go through adapters like this: > <http://www.dx.com/p/5v-rj45-female-to-rj45-male-dc-male-dc-female-power- > over-ethernet-poe-adapter-black-208704> So, the most you'll need to > protect against is 24VDC.
Yes. But if the passive poe is only used on one jack, then that jack should already have been assigned and in use. So it is not available for someone to accidentally plug another RJ-45 in that socket.
>>I'll add a shutdown circuit to disable the >>connection if the voltage exceeds +5V or so. I know you say it should >>not be a problem since the handshake is so complex, but things do go >>awry.
> Not exactly. I said with 802.3af and similar active PoE systems, you > should not have a problem. It's the passive power sources, that have > no smarts and often no protection, that is likely to cause problems.
Yes, passive poe is the thing I am concerned about.
>>I'd >>hate to have to argue with a customer that my equipment failed because >>there was excessive voltage on the plug:)
> You will anyway. There is wide range of contrivances that use RJ45 > connectors that might do damage. Short list: > Motorola, Kenwood, Yeasu, and Icom 2-way radio mic connectors. > Video terminals and teletype machines. > RJ45 RS232 devices such as terminal servers. > Light pens. > Many telephone systems (all with PoE). > Whatever else I forgot. > It will be difficult to protect against all these.
Good list. Hopefully none of these will be anywhere near the system when it is installed.
> Besides users that cram a USB connector into the ethernet jack, > there's also the problem of the gold wire connections being mangled > inside the RJ45 jack. Three ways that I know of to do that: > 1. Cram something into the RJ45 that doesn't belong and wiggle. > 2. Use an RJ11 or RJ14 plug in an RJ45 jack. (More on this below) > 3. Cram an RJ45 plug into the jack which was NOT crimped. > The result of all of these is to have the gold wires in the jack move > over a notch, thus shorting two adjacent pins together. If the > adjacent pin carries power, it might blow something up. Internally, > the jack has a plastic "comb" that acts as a separator and spreader > for the gold wires. It doesn't take much to lift a gold wire from the > comb, move it to the adjacent slot, and produce a short.
Amazing what some people can do. I had one customer who plugged DE-9 connectors in upside down. It must have taken a huge amount of force.
> The mangled RJ45 has become common enough that designers are defending > themselves by making the connector an easily replaceable part. Most > common is using a dual RJ45 "barrel" connector. Something like this: > <https://www.amazon.com/Waterproof-CAT5e-RJ45-Feed-Thru-Coupler/dp/B00CUL > LAWE> If the connector gets mangled, just unplug, remove and replace.
Looks like they have the nut on the wrong side of the gasket.
> Anyway, good luck.
On 12/03/18 23:56, Steve Wilson wrote:
> Since modern computers have no serial or parallel interfaces, the old GPIB > and RS-232 interfaces are obsolete. There have been discussions about other > interfaces such as HDMI, but the connector is a bit large. > > Consider a setup with a controller connected to the LAN. It may need to > connect to several or dozens of separate boxes for measurement and control > functions. Is it a good idea to use RJ-45 for these interfaces also? > > The connectors are small, locking, bidirectional, high speed, cable length > up to 300m, very inexpensive, readily available, and have sufficient pins > for most needs. > > https://en.wikipedia.org/wiki/Modular_connector > > The RJ-45 pinouts are well defined and can probably be used as is. One > issue is with POE, power over ethernet. The voltage applied can be 48V, > which could destroy most electronics if not controlled. The spec says it > can only be applied if there is a proper handshake between source and load, > but that could go awry. > > The cables can be double-shielded and come in various lengths and colors. > Here are some examples: > > "When a regular shield is not enough, L-com's exclusive double-shielded > SF/UTP patch cables are ideal. Category 6 tested, these cables use L-com's > superior shielding to drastically reduce EMI/RFI interference using a 100% > foil plus a 65% braid shield. The Low Smoke Zero Halogen jacket allows this > industrial patch cable to meet today's environmental and safety > requirements. With 26 AWG stranded conductors, this cable is flexible and > easy to install even in tight spaces. We stock in full lengths up to 100 > feet so that equipment runs can be pulled directly and simply plugged into > either end." > > https://tinyurl.com/pf3p4xg > > "Tera Grand - Premium CAT7 Double Shielded 10 Gigabit 600MHz Ethernet Patch > Cable for Modem Router LAN Network - Built with Gold Plated & Shielded RJ45 > Connectors, 3 Feet White" > > https://tinyurl.com/ya472pcr > > "Cat 7 Shielded Ethernet Cable 5 ft 6 Pack ( Highest Speed Cable ) Cat7 > Flat Ethernet Patch Cables - Internet Cable for Modem, Router, LAN, > Computer - Compatible with Cat 5e, Cat 6 Network" > > https://tinyurl.com/y7sfsx9w > > What are your thoughts? >
If you want isolation, you need co-ax, not twisted pair. We're designing an RF prototyping platform that will use thin co-ax jumper leads, with U/FL (IPEX) or MMCX connectors. Clifford Heath.
Clifford Heath <no.spam@please.net> wrote:

> If you want isolation, you need co-ax, not twisted pair.
> We're designing an RF prototyping platform that will use > thin co-ax jumper leads, with U/FL (IPEX) or MMCX connectors.
> Clifford Heath.
Thanks. I need bidirectional control, and would like to minimize RFI to external circuits. Ordinary unshielded CAT5 seems to have little radiation, and shielded and double shielded should be even better. Coax is single-ended, so radiation from sharp transitions can be a problem. Twisted pair is balanced, which reduces transition noise. The coax shield can lead to ground loop problems. RJ-45 is inherently isolated by the coupling transformers. In the case of ground loop problems, there is no need to ground the shields at both ends since they are not involved in data transmission. One end can connect to ground, and the other end to the case through a 100k resistor in parallel with a 0.1uF or 0.01uF bypass cap to reduce risk to ESD. Recall there are many diffeent versions of coax. Some of the cheap versions are only good to perhaps -80dB. Double shielded coax is better, but it can be very stiff. Some double shielded RJ-45 cables are advertised to be very flexible.
Steve Wilson wrote:
> Clifford Heath <no.spam@please.net> wrote: > >> If you want isolation, you need co-ax, not twisted pair. > >> We're designing an RF prototyping platform that will use >> thin co-ax jumper leads, with U/FL (IPEX) or MMCX connectors. > >> Clifford Heath. > > Thanks. I need bidirectional control, and would like to minimize RFI to > external circuits. Ordinary unshielded CAT5 seems to have little radiation, > and shielded and double shielded should be even better. > > Coax is single-ended, so radiation from sharp transitions can be a problem.
What's that supposed to mean?
> Twisted pair is balanced, which reduces transition noise.
Coax is balanced too, with the current on the central conductor being accompanied by an equal and opposite current along the shield. Equal to 0.03% or so, better than twisted pair.
> > The coax shield can lead to ground loop problems. RJ-45 is inherently > isolated by the coupling transformers. In the case of ground loop problems, > there is no need to ground the shields at both ends since they are not > involved in data transmission. One end can connect to ground, and the other > end to the case through a 100k resistor in parallel with a 0.1uF or 0.01uF > bypass cap to reduce risk to ESD.
[...] Nothing prevents the use of coupling transformers at the end(s) of a length of coax. Jeroen Belleman