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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)

#11

Post by Retr0id »

xyphro wrote: post #10
Retr0id wrote: post #8

Interesting. I built an AR488 a while back ( https://github.com/Twilight-Logic/AR488 ) and it worked alright for my needs. I'd be interested to see a comparison of the two projects.

Here a comparison from a user: https://github.com/xyphro/UsbGpib/discussions/47

Ooh! The faster speeds would be very welcome, I was bothered by the slowness of the AR488 but I assumed that was just how GPIB was (I had no baseline to compare to). I'll switch over when I get a chance.

That user's project also looks very interesting - My TDS684A's CRT seems to have died, and rather than fix it I could switch to using a software scope.

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

#12

Post by sokoloff »

YakBizzarro wrote: post #6

Maybe someonw can explain me, but I never understood the appeal of GPIB for modern instruments (legacy instruments are of course "excused"). Electrically is a terrible interface that introduces ground loops with the control computer. Speed are laughable and it requires exensive and exotic adapters with complex sw stack (I wish this projects good success, it's needed!). Ethernet in comparison tick all my boxes. It's e…

Nothing, other than perhaps just much high-quality legacy equipment is out in the field that still works fantastically.

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

#13

Post by xyphro »

YakBizzarro wrote: post #6

Maybe someonw can explain me, but I never understood the appeal of GPIB for modern instruments (legacy instruments are of course "excused"). Electrically is a terrible interface that introduces ground loops with the control computer. Speed are laughable and it requires exensive and exotic adapters with complex sw stack (I wish this projects good success, it's needed!). Ethernet in comparison tick all my boxes. It's e…

If you buy used equipment which doesn't have Ethernet or your company wants you to ise the stuff that is in the Lab since 10+ years there's simply no other choice. Or companies that see Ethernet as a potential security attack vector. It's indeed not that GPIB is better than Ethernet. In tiny aspects that's argueable, but as general statement true.

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

#14

Post by xyphro »

Retr0id wrote: post #11
xyphro wrote: post #10

Earlier quoted context omitted.

Here a comparison from a user: https://github.com/xyphro/UsbGpib/discussions/47

Ooh! The faster speeds would be very welcome, I was bothered by the slowness of the AR488 but I assumed that was just how GPIB was (I had no baseline to compare to). I'll switch over when I get a chance. That user's project also looks very interesting - My TDS684A's CRT seems to have died, and rather than fix it I could switch to using a software scope.

The upcoming V3 adapter reaches even more than 1 MByte/s with my fastest instruments. Unless you connect long GPIB cables to it, because capacitive load slows down GPIB as it self regulates speed down in the way GPIB is designed.

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

#16

Post by xyphro »

bsder wrote: post #7

I strongly suspect that this does not meet the strict timing requirements that GPIB has. Putting this on your bus is likely to violate both the T1 hard timing requirements and the impedance requirements. Use of the "standard" set of 74-series buffers that everybody uses would meet impedance requirements and would also allow the usage of a much faster MCU which likely could be made to adhere to the strict T1 timing re…

For a situation where the instrument is directly connected to the adapter like here there is no difficulty in fast T1 timing on a MCU. V3 will have btw. fully compliant GPIB electrical specs without 74 series buffers. 48mA drivers are not required for a direct connection scenario as V2 supports. VIH is a bit violated, though not practically meaningful. So far I heard of no device not working after over 6 years and those who did not in early stages I managed to get running with sw updates. This is not a one shot plain textbook GPIB simple thing implementation, it's years of iterations, debug, improvement.

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

#17

Post by [deleted] »

Retr0id wrote: post #11
xyphro wrote: post #10

Earlier quoted context omitted.

Here a comparison from a user: https://github.com/xyphro/UsbGpib/discussions/47

Ooh! The faster speeds would be very welcome, I was bothered by the slowness of the AR488 but I assumed that was just how GPIB was (I had no baseline to compare to). I'll switch over when I get a chance. That user's project also looks very interesting - My TDS684A's CRT seems to have died, and rather than fix it I could switch to using a software scope.

[deleted]

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

#18

Post by [deleted] »

YakBizzarro wrote: post #6

Maybe someonw can explain me, but I never understood the appeal of GPIB for modern instruments (legacy instruments are of course "excused"). Electrically is a terrible interface that introduces ground loops with the control computer. Speed are laughable and it requires exensive and exotic adapters with complex sw stack (I wish this projects good success, it's needed!). Ethernet in comparison tick all my boxes. It's e…

[deleted]

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

#20

Post by labcomputer »

YakBizzarro wrote: post #6

Maybe someonw can explain me, but I never understood the appeal of GPIB for modern instruments (legacy instruments are of course "excused"). Electrically is a terrible interface that introduces ground loops with the control computer. Speed are laughable and it requires exensive and exotic adapters with complex sw stack (I wish this projects good success, it's needed!). Ethernet in comparison tick all my boxes. It's e…

> 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, sure, you can add the same capability with a programmable pulse generator connected via coax to the trigger input of all your instruments, but GBIP lets you do that with just the data connection (and you don’t always have a spare trigger channel). The only other protocols I know of with similar capabilities are PXI and PXIe, which are “PCI(express) in an incompatible form-factor, plus some extra signals for real time synchronization”.

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