Electronics > Metrology

Yaugi 4: GPIB Ethernet PoE Adapter

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essele:
Just about a year ago I first posted about a project I was working on to produce a USB to GPIB adapter along the lines of many others you could buy, but with a goal of being somewhat lower cost.

https://www.eevblog.com/forum/metrology/yet-another-usb-gpib-interface-(yaugi)/msg2744372/#msg2744372

Anyway ... I have continued developing this, but have switched away from USB in favour of ethernet, and specifically PoE (802.11af) ... it's not ready yet, but I've seen a few things over the last few days that's made me think I should talk about what I'm doing.

It's designed to be a single device controller, so not intended to run a long chain of GPIB cables, the idea being that they should be low cost enough that you just throw one in each device. I understand that might not be ideal from a triggering perspective, but given most new devices are ethernet based and not GPIB I'm sure it's not the end of the world.

I've redesigned the GPIB handshake and moved it from software bit twiddling into the programmable logic on the PSoC device, so it's much faster, it also has a hardware timeout mechanism and so far I've not managed to lock it up at all.

It uses a W5500 ethernet controller and I've implemented (from scratch) a DHCP client, a mDNS responder, a VXI11 rpc based client, and a web server to handle config and even firmware updates. (Now you know why it's been a year!) It also accepts TCP and UDP based queries, so can be used with things as simple as nc. It also seems to work ok with LabView and other NI tools although I've only done very rudimentary testing.

I'm using a Silvertel Ag9900 PoE module, which really feels like the lowest cost way of achieving PoE (and now are available from Mouser, the first few I had to get direct!) Still mulling whether to add a USB port for power in for non-PoE scenarios.

I've got a version with the GPIB connector directly on the PCB (see photo in 3d printed case) and I've just built another version with an IDC connector and ribbon cable, which I think is more practical for use behind kit in tight spaces etc.

So far it's largely working, I still need to implement the VXI11 abort and interrupt channels, and there is still a fair amount of work to do on the web browser and web based UI.

My best guess at this point (as I've just found some lower cost ethernet magjack options) is that at small scale this is likely to be $30 to $40 of board and components. My last order of 5 assembled IDC ones from JLCPCB was $40 + shipping/tax and you just need to add the PoE module, PSoC, MagJack, and ribbon cables/connectors.

Interested in thoughts/feedback. No commercial intent - doing it for my own use, and will be very happy to share once it's working reasonably well.

(And yes, there is a bodge wire in the photo ... my new MiniProg4 seems to be missing a pull-up on the UART so receives garbage during reset and programming, so this will be added on the next revision, but only needed for debug)

Lee.

ve7xen:
I really like the concept. PoE power is a nice idea, just get a small PoE switch and power several of these on the bench from one power supply. Much prefer it to janky USB solutions for this, even if it is a bit more expensive.

I'd be concerned about availability of the PoE module, especially if you're presenting this as a project for DIYers and not a product for sale, but for your own personal use, who cares! It doesn't seem to be available from any of the normal suppliers; at a glance I can't even find anywhere to buy it online in singles. I assume it's also fairly expensive - curious where you got them from? There are lots of integrated PoE-PD / DC-DC converter ICs available on the market (e.g. NCP1083, Si3404, TPS23757), even if it's a somewhat larger footprint, I think I'd rather a discrete implementation. Probably cheaper too, if you're doing this in quantity.

essele:
Thanks ve7xen.

I'm fairly confident the PoE modules are reasonably available, when I first started looking at this I had to get them "direct" (was actually through a distributor, but I was able to buy 2 modules at a reasonable price even with shipping to the UK), but now they are available at Mouser...

https://www.mouser.co.uk/ProductDetail/silvertel/ag9905lp/?qs=OlC7AqGiEDm9ZoM6zJQCoQ==&countrycode=GB&currencycode=GBP

I did look at a discrete implementation as I think I would prefer it, but I couldn't find any way of doing it that was going to be lower cost, and definitely would have used more board space. I even looked at the IC's used in the silvertel module, but couldn't figure out what they are.

If anyone has a suggestion that's going to beat £6 then please let me know.

dietert1:
This is a great project, if you implement a nice subset of VXI and if it works reliable. About ten years ago i made some USB-GPIB adapters based on a XILINX CPLDs and FTDI USB-parallel chips. Those GPIB adapters have been running for months. Usually until the DLINK USB hub gets stuck, maybe when someone touches the cables.

As far as i remember POE is something in the making. It started as something simple to supply IP Phones, but nowadays it can supply a PC. Meanwhile power conversion got sophisticated rules and signalling, that can't be implemented without special chips. As far as the chip implements all the rules it should be/will be tolerant to future POE upgrades. The situation compares well to the different USB standards, if you consider those USB-C connectors Apple introduced.

Regards, Dieter

ve7xen:
Oh yeah, I didn't realize the part number is slightly different than the series number |O. Looks to be available at Mouser at least, so that's not so bad.

About $9 USD for the module doesn't seem too bad in small quantity. In larger quantity I'd be confident the discounts are going to ramp much faster on the discrete components, especially the magnetics. And sometimes magnetics availability is an even bigger problem! In onesy-toosies, wouldn't be surprised if it's similar / more to do it yourself. Fair enough decision.

As a quick thought experiment, I took a look at the Si3404 EVB isolated flyback configuration. Assuming passives are free, adding up the transformer and active components I get about $8 USD at qty 1. Add a dollar or so for passives and it seems slightly more expensive at low quantity (looks like the folks at Silvertel did their homework lol). At high quantity sourcing most of the stuff from Asia, the gap widens pretty quickly, at only qty 100 it's down to about $5.50.

Technically isolation is required for this, since it connects to an external device (the test equipment), but in practice you could probably get away without it and it greatly simplifies / shrinks the design. If you did that, I think you'd be closer to $4 at qty 1 and $3 and qty 100.

Doing PD-powered gadgets (or just a breakout board) has been something on my mind for a while so it's interesting to evaluate the options, and good to know about those Ag modules.

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