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Open source USB to GPIB converter (for Test and Measurement instruments)

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Re: Open source USB to GPIB converter (for Test and Measurement instruments)

#31

Post by jonah-archive »

rowanG077 wrote: post #26
labcomputer wrote: post #20

Earlier quoted context omitted.

> What am I missing? Not much, but consider latency: You can use the Group Execute Trigger (GET) to simultaneously trigger multiple instruments with both very low latency and very low latency dispersion. Think, easy-to-use sub-microsecond synchronization. Ethernet and USB 4 may have orders of magnitude more bandwidth, but can’t achieve the same multi-device synchronization capability without side channel signals. Now…

sub-microsecond triggering should be doable with a level-2 cut-through switch and an ethernet broadcast no? I admit that ethernet is not really designed for that as the Phy is then the latency bottleneck.

There are approaches to real-time ethernet (some industry implementations like profinet or ethercat, 802.1as from IEEE) but support is spotty and it requires specialized gear to be effective.

Re: Open source USB to GPIB converter (for Test and Measurement instruments)

#33

Post by ChrisMarshallNY »

emmelaich wrote: post #32
ChrisMarshallNY wrote: post #15

I cut my teeth on IEE-488. I didn’t realize that it was still a thing.

Crazy to think that the first HP9000 (PARISC) computers used GP-IB (aka HP-IB) for accessing disks !

I used one of those (and an even older little workstation that I forget the name) to program GPIB ("HPIB") systems.

This is my first ever engineering project, as a newly-minted electrical engineer (downloads a PDF): https://littlegreenviper.com/wp-content/uploads/2022/07/TF30...

Re: Open source USB to GPIB converter (for Test and Measurement instruments)

#34

Post by stagger87 »

georgeburdell wrote: post #23

Great work making this available for sale. NI and Keysight are the only two traditional vendors of this kind of thing and they’re priced close to $1k these days. There are tons of knock-offs on Ebay that won’t last more than a few months if they ever work.

FWIW, You can buy legit used 82357s for quite a bit less than 1k. Anecdotally, I've never had one fail in 20 years. Probably bought a dozen over that time frame. All used daily.

Re: Open source USB to GPIB converter (for Test and Measurement instruments)

#35

Post by Neywiny »

georgeburdell wrote: post #23

Great work making this available for sale. NI and Keysight are the only two traditional vendors of this kind of thing and they’re priced close to $1k these days. There are tons of knock-offs on Ebay that won’t last more than a few months if they ever work.

Even worse, the windows drivers know they're knock offs and let you use them for a bit and then error out. It's the perfect lesson. They give you that high of "yes, I got one over on the big guys, we're cruising now" and then "I don't know boss it's just all of a sudden not working anymore. Yes I know we're in a production crunch. Yes we should've just bought the real one". On Linux though, no issues for me

Re: Open source USB to GPIB converter (for Test and Measurement instruments)

#36

Post by labcomputer »

rowanG077 wrote: post #26
labcomputer wrote: post #20

Earlier quoted context omitted.

> What am I missing? Not much, but consider latency: You can use the Group Execute Trigger (GET) to simultaneously trigger multiple instruments with both very low latency and very low latency dispersion. Think, easy-to-use sub-microsecond synchronization. Ethernet and USB 4 may have orders of magnitude more bandwidth, but can’t achieve the same multi-device synchronization capability without side channel signals. Now…

sub-microsecond triggering should be doable with a level-2 cut-through switch and an ethernet broadcast no? I admit that ethernet is not really designed for that as the Phy is then the latency bottleneck.

Sure, in principle, but that takes effort and special equipment to set up. The point is that GPIB makes it easy (trivial, actually) with nothing more than the cables you normally use to connect instruments to get very low and predictable latency.

GPIB GET works by first configuring a subset of bus devices as listeners and then sending a single-byte message (it’s an 8 bit bus, so one bus cycle) with the ATN line asserted. It’s intrinsically low latency without any special effort.

Whether that makes it worthwhile to put GPIB on a new instrument in 2025 is a different question. I’m only addressing “what does GPIB give you”?

Re: Open source USB to GPIB converter (for Test and Measurement instruments)

#38

Post by elevation »

If you control your application stack, you can pivot from expensive NI GPIB hardware to something cheaper. Besides prices, you get the advantage of not requiring a 1.5GB Windows-only NI MAX install on a PC just to connect to the device.

Since I hadn't heard of open source hardware, I bought 5 of these [0] instead around 2020 and they've been reliable for daily lab use. You just connect to them over TCP and send a couple of commands to select the GPIB addr to correspond with; after that, you can send SCPI commands the same way you always do.

[0]: https://prologix.biz/

Re: Open source USB to GPIB converter (for Test and Measurement instruments)

#39

Post by xyphro »

elevation wrote: post #38

If you control your application stack, you can pivot from expensive NI GPIB hardware to something cheaper. Besides prices, you get the advantage of not requiring a 1.5GB Windows-only NI MAX install on a PC just to connect to the device. Since I hadn't heard of open source hardware, I bought 5 of these [0] instead around 2020 and they've been reliable for daily lab use. You just connect to them over TCP and send a cou…

A good way around application overloaded applocation stacks is R&S Visa which is lean and mean while still exposing full visa to applocations like labview. Or going with something like python usbtmc. If you also have other instruments to control e.g. with usb or ethernet you'll likely anyway look into a visa.

Re: Open source USB to GPIB converter (for Test and Measurement instruments)

#40

Post by xyphro »

georgeburdell wrote: post #23

Great work making this available for sale. NI and Keysight are the only two traditional vendors of this kind of thing and they’re priced close to $1k these days. There are tons of knock-offs on Ebay that won’t last more than a few months if they ever work.

Yes, it is easier to fall into the trap of getting a clone, even if you think you buy an original one.
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