RJ-45 for instrument interface

That would be the style like it is used with the Red Pitaya.

< >

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

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: 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.

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.

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: 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 
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Skype: JeffLiebermann     AE6KS    831-336-2558

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 termina l emulation (but that's another issue).

I guess I'm asking, if I place an FTDI on our board, how much is involved i n 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!!!

FWIW: I just purchased a chip burner that still has a parallel port.

g one of these FTDI chips, or do I have to jump through Windows hoops?

nal emulation (but that's another issue).

in getting a "dumb terminal" to manifest on the PC side? There would onl y ever be one of our devices on the FTDI bus (if that matters). IOW, I do n'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

What's a "chip burner"? Is that anything like a pellet burner and why does it need any port? ;-)

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?

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

I have a UART (serial RS232, 19200 baud).

one of these >FTDI chips, or do I have to jump through Windows hoops?

al emulation

d only ever be one of our devices on the

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 ex pect 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

Max length for Ethernet over copper is 100 meters. If you need to go farther, use fiber.

Regards

Thanks, but this is not to interface to existing commercial test equipment. It's a general interface to custom designs.

I'm thinking of the html interface used to configure a router. You can enter numbers and use checkboxes to set options. DD-WRT, Tomato, and OpenWRT might be a place to start. Here's a link to an Infoworld review:

Thanks again for the excellent advice. I'm not trying to run POE. 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'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. I'd hate to have to argue with a customer that my equipment failed because there was excessive voltage on the plug:)

I finally got a chance to look up passive poe. Thanks for mentioning it. That's exactly the kind of thing I was worried about.

I'll add a shutdown circuit to disable the connection and light a fault led.

Of course, I'll take power from the passive poe to do this:)

With such unique identifications and some udev magic (SYMLINK+=...) you can even have device names automatically assigned in Linux.

--
Reinhardt

BK-867 here. Wonderful device!

I have a (much) older one, but it started to become a hassle keeping a Windows-95/XP machine around to run it. And it doesn't handle many of the newer chips without jumping through a lot of hoops.

On Monday, March 12, 2018 at 8:37:42 PM UTC-4, snipped-for-privacy@gmail.com wrote: Thanks guys. I'm going to look into those FTDI chips in more detail.

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.

Meh, I have had annoyance when I wanted to locate such an instrument more than 25m from the computer that controlled it. (And incidentally the cable had to be chopped, fed through a small hole and reterminated which is not nice with USB.) I could have opened the instrument and removed the FTDI chip and replaced it with a MAX232 or equivalent, but that would void the instrument warranty. I considered trying to buy/make the opposite of a FTDI chip (USB host with a uart) but that is a massive pain because USB is so complicated.

Also, such an instrument (with built-in FTDI) is impractical to interface to e.g. an Arduino or other simple microcontroller, if you wanted to do that. You need a real OS with USB stack, but sometimes it is better to avoid putting a real PC or even a RPi in your test system, because then the corporate IT department feels entitled to mess with it, install corporate spyware and updates that break it, etc.

Really, if you want to sell me something that looks like a FTDI dongle connected to an instrument with a serial port, then put a real serial port on the instrument and screw on a FTDI dongle, on the outside. Yes it is a waste of a dollar worth of level shifters but it is better. No, I don't care if it will confuse millenials with that strange ancient connector. Actually, go ahead, hook up and require all of the handshaking pins, just to mess with them.

It would be nice if everything were wireless. We wouldn't need a tangle of hubs and cables.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics