Forums

RJ-45 for instrument interface

Started by Steve Wilson March 12, 2018
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. -- Mike Perkins Video Solutions Ltd www.videosolutions.ltd.uk
Am 12.03.2018 um 21:20 schrieb Steve Wilson:
> Gerhard Hoffmann <gerhard@hoffmann-hochfrequenz.de> wrote: > >> Am 12.03.2018 um 20:58 schrieb Steve Wilson: >>> John Larkin <jjlarkin@highlandtechnology.com> wrote >> If you need to >>> go long distances, go Ethernet but that's a bit more >>>> work. > >>> Yes, I need to go Ethernet. > >> I did that with a BeagleBoneBlack. > >> Just ssh to it. vi / gcc / make / USB / Ethernet drivers / >> flash disk... everything already there. Just bang the port bits >> or use the i2c... of the chip set. > >> regards, Gerhard > > Thanks. I'm thinking to use HTML as the interface to the host, so I probably > want full Linux. >
That would be the style like it is used with the Red Pitaya. < https://www.redpitaya.com/c96/stemsuplabsup-125-14 > I have one here, but this WebInterfave / Vivado style is quite different from the C/VHDL mode I am used to. It's only the cultural shock. :-) regards, Gerhard
On Mon, 12 Mar 2018 20:10:47 GMT, Steve Wilson <no@spam.com> wrote:

>I do not need or want POE, I'm just >concerned about someone plugging a cable in the wrong socket.
If you need some entertainment, try plugging a USB Type A plug into an RJ45 ethernet jack. It fits quite nicely. If the vendor supplies passive DC power: <https://help.ubnt.com/hc/en-us/articles/115000263008--UniFi-Understanding-PoE-and-How-UniFi-Devices-are-Powered#active%20vs%20passive> on the RJ45 jack, the metal USB connector shield will blow a fuse or a current limiter (hopefully with foldback) will limit the amount of smoke generated. There are vendors out there that supply 5V, 12V, or 24VDC on the ethernet jack, with maybe some protection. For example, the above URL shows that Ubiquiti still supplies 24VDC passive power on some products. I haven't had time to tear one of their power injectors apart to see what's inside. I haven't had any problems with them, so as long as I don't do something dumb, I guess I'm ok.
>When you say "deliver full power", does that mean the POE can deliver >partial power by itself or if it is misconfigured?
No. DC power is delivered only after the negotiated handshake and identification ceremony. You can short the PoE power wires to each other or to ground with creating a problem. However, connecting the power wires across the ethernet data lines will be a big problem because they're looking into a DC coupled transformer with about 0.5 ohms resistance. I don't recall the fusing current, but it's not much. That won't happen with 802.3af style active PoE, but is real possibility with passive PoE.
>I don't want to have to >deal with 48V no matter what other faults may exist. 48V is not the >problem, the difficulty is getting rid of the heat. I could add a shutdown >circuit, but that adds complexity and another failure mode.
The PoE chips deal with the 48V for you. I'll assume that the heat you're worried about is whatever gets hot if things go awry. As I mentioned, nothing is going to blow up, get hot, fuse, or explode with proper 802.3af chips, but might with passive power. I don't have a problem with complexity if it also adds safety. I'm not suggesting that it's foolproof. Our technology is quite good at producing better fools: <https://community.spiceworks.com/topic/313729-almost-fried-my-switch-with-poe-injector> <https://www.reddit.com/r/sysadmin/comments/4lbnq7/til_never_test_a_passive_poe_connection_on_a_non/> If you tried to design a PoE system that is rugged, reliable, foolproof, and safe, you'll probably end up with something similar to 802.3af. Spare yourself the effort and just use the available technology and chips. -- 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
On Monday, March 12, 2018 at 10:59:14 AM UTC-4, John Larkin wrote:
> 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.
John, for a current project: I have a UART (serial RS232, 19200 baud). If I wanted to connect to it via USB, is it really as simple as just using one of these FTDI chips, or do I have to jump through Windows hoops? I just need a "dumb terminal", although I wouldn't mind having some terminal emulation (but that's another issue). I guess I'm asking, if I place an FTDI on our board, how much is involved in getting a "dumb terminal" to manifest on the PC side? There would only ever be one of our devices on the FTDI bus (if that matters). IOW, I don't think I care how it enumerates? Thanks!!!
On Monday, March 12, 2018 at 12:58:52 PM UTC-4, Phil Hobbs wrote:

FWIW: I just purchased a chip burner that still has a parallel port.
Den tirsdag den 13. marts 2018 kl. 00.28.25 UTC+1 skrev mpm:
> On Monday, March 12, 2018 at 10:59:14 AM UTC-4, John Larkin wrote: > > 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. > > John, for a current project: > I have a UART (serial RS232, 19200 baud). > If I wanted to connect to it via USB, is it really as simple as just using one of these FTDI chips, or do I have to jump through Windows hoops? > > I just need a "dumb terminal", although I wouldn't mind having some terminal emulation (but that's another issue). > > I guess I'm asking, if I place an FTDI on our board, how much is involved in getting a "dumb terminal" to manifest on the PC side? There would only ever be one of our devices on the FTDI bus (if that matters). IOW, I don't think I care how it enumerates? Thanks!!!
just plug it in (the driver come with most OSs) and it appears as a regular comport open a terminal program and open it as any other serial port
On Mon, 12 Mar 2018 16:30:06 -0700 (PDT), mpm <mpmillard@aol.com>
wrote:

>On Monday, March 12, 2018 at 12:58:52 PM UTC-4, Phil Hobbs wrote: > >FWIW: I just purchased a chip burner that still has a parallel port.
What's a "chip burner"? Is that anything like a pellet burner and why does it need any port? ;-)
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?
On Mon, 12 Mar 2018 16:30:06 -0700 (PDT), mpm <mpmillard@aol.com>
wrote:

>On Monday, March 12, 2018 at 12:58:52 PM UTC-4, Phil Hobbs wrote: > >FWIW: I just purchased a chip burner that still has a parallel port.
We use the B+K 844 USB programmers, which are actually rebrands of some box made in eastern Europe. They work great. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
>John, for a current project:
I have a UART (serial RS232, 19200 baud).
>If I wanted to connect to it via USB, is it really as simple as just using one of these >FTDI chips, or do I have to jump through Windows hoops?
>I just need a "dumb terminal", although I wouldn't mind having some terminal emulation >(but that's another issue).
>I guess I'm asking, if I place an FTDI on our board, how much is involved in getting a "dumb >terminal" to manifest on the PC side? &nbsp; There would only ever be one of our devices on the >FTDI bus (if that matters). &nbsp; IOW, I don't think I care how it enumerates? &nbsp;Thanks!!!
Yeah, it's about that easy. The FTDI driver works in Windows and Linux at least. If you get a Parallax Prop Plug, you can test it out yourself. We (and I expect lots of others) just copied the published schematic. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net https://hobbs-eo.com