I have several pieces of HP gear (DMM, counter, Agilent-branded triple-output supply) I'd like to connect to a National Instruments USB to GPIB adapter for some measurements.
IEEE 488 is somewhat before my time and I see that the connectors are stackable, is there a preferred bus topology for a few pieces of gear? Star, linear/daisy chain with the stack on the interface, linear/daisy chain with the stack on the first piece of gear? Does it matter much in this use case?
Daisy chain, no more than two connectors per unit as the accumulated weight gets problematic.
Not to mention the torque, when someone tugs on a cable.
I believe that folks have been known to do a star connection, with the center node being just cables, for that reason.
The interface speed is less than 1 MHz, even when externally clocked, so it’s all the same electrically.
Cheers
Phil Hobbs
That's a mechanical problem, not a bus signaling problem.
Phil H's comment seems to support that they can electrically be stacked, mechanical support problems aside.
IEEE488 is surprisingly tolerant of abuse and unless you have very fast (for the day) transient recorders you won't be pushing the speed limits. The whole thing is good for about 1MHz flat out if your drivers are up to it. Most DVM and test kit is pretty slow but fast enough to be handy.
At 1MHz topology hardly matters but mechanical considerations do! We used to use custom IEEE488 cables much longer than the approved length on big kit with only a minor slowing down (that was on the HP chipset). ie. One longish 5m cable and a few 1m/2m ones at the far end.
Just beware of stacking them more than 3 deep or the stress on the connector can pull the board out of the PC. Also beware of metal turnings or be sure to have plastic caps on all the stackable backs.
By the way, if anyone is after a GPIB to USB adapter that is cheap, look at the AR488 arduino firmware. I used it to back up the battery backed SRAM in my HP3478A.
Hoping to use SciPy/Numpy with a National Instruments GPIB-USB dongle on a Linux machine.
There's a wonderful tech-surplus warehouse of the old fashion in the Boston area, they sell the USB interfaces at $50 and 1 meter L-com/Belkin/assorted brand GPIB cables at $10 a pop
Have gpib based test gear all around the lab, beyond the limit of cables, which are clunky and heavy anyway. Solution here was the Prologix lan to hpib adapter, which puts the test gear on the local subnet, where it belongs. Have written an os package to drive it, so that at top level, it's all shell scripts, and Can be built and controlled by any unix with gcc and a shell, even cygwin on windows.
Prologix used to be quite low cost, but they have raised the price considerably since, which is a pain, but still lower than the lan / hpib adapters from HP or NI...
Chris
As I already posted, there is an open source project called AR488 which uses an Arduino to convert USB to/from GPIB. google AR488
There is a board which you can get made at OSHpark cheaply which adapts the arduino pinout to the connector.
There are relatively cheap connectors without the jack screws and daisy-chaining capability that you can use because you do not require the ability to daisy chain other cables onto the back of your USB adapter.
One shortcoming it has is that it will draw current from the GPIB bus if the USB cable is not powered, but it is easy to avoid doing that.
It's to go on the back of a GPIB instrument. It doesn't need to be small, but it is no bigger than a normal GPIB connector. It uses a small arduino "pro micro".
If someone had intergated all of the components onto the same PCB as the GPIB connector I would have avoided that design. It is easier to buy an arduino than to build one, and probably cheaper too if you only want exactly one of them. The adapter PCB was very cheap and building the whole thing was very quick. That is what I wanted. I just wanted to back up the SRAM in my DMM before its battery went flat and lost the calibration settings, or before I accidentally erase the SRAM in the process of replacing the battery.
Yes, and if you're doing that, it is cheaper to use the arduino adapters than National Instruments, software permitting.
I don't like USB, but a lot of software and hardware is set up to use it, so as long as someone else deals with the details of the USB stack and it works, I won't complain too loudly. If I have to write the low level software I will try to use something else.
The variety is there because of a long history of changes to induce people to buy new things. Thus it will ever be.
Jeroen Belleman
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