Introduction

Almost every electronics lab equipment has the possibility to be controlled remotely. This is almost always done by using IEEE-488. Also known as ” HP-IB” As HP called it when HP developed this 8 bit parallel bus.   It’s also know as “GPIB”. (General Purpose Interface Bus).

In the old days a dedicated computer card was used as a controller, to perform remote operations on the lab equipment.

Nowadays we have LXI for example, making it possible to remotely control devices over Ethernet network by using the TCP/IP protocol. This doesn’t mean GPIB isn’t used anymore. Even modern equipment can have a IEEE-488 interfaces. For example my Rigol DM3608 has a IEEE-488 interfaces and can be configured to understand a specific command set.

Use an IEEE488(GPIB) communication -adapter

Nowadays it’s more common to use USB GPIB controllers to remotely control the (old) lab equipment.  There are a couple of choices:

• Use Prologix GPIB-USB
• Use an IEEE488(GPIB) communication -adapter (Keithley or National Instruments for example)
• These adapters may also be available as Ethernet controllers which plug into a LAN network.

However there are mainly two difference between the “brand names” and the Prologix:

For example the National Instruments (NI) USB controller present itself as a GPIB device. Whereas the Prologix presents itself as a serial device.

Which one to choose ?

If you look at the known brand names one, presenting them self as a gpib device, you notices these devices are not cheap. A new adapters can cost you as much as $1300,00 and no.. this is not a typo. While the Prologix adapter cost around $150,00 dollars.. So what’s the catch ? (there is always a catch).

And as always: It’s depends. Say for instance that you want to use an application from a vendor which only works with a GPIB device. The Prologix in this case won’t work. At least not out of the box.

On the other hand: If you’re about to write your own data log / measure applications, the Prologix might be a perfect solution, since  it’s a serial device, and you don’t have the overkill of using the NI-VISA drivers (for example)

Then there is of course the price. Luckily the GPIB USB adapters can be found relatively cheap second hand. I did found a genuine NI  GPIB USB-HS new in box for a around $150,00 dollar. Which brings these adapter in the price range of the Prologix one.

Comparing a Prologix and a NI GPIB USB-HS adapter

Since I have both types, let’s compare them in practice. To compare the adapters i’m going to use them in the following scenarios:

• Using the adapters with a existing application from a vendor (Rohde Schwarz WINIQSIM) which is a Windows application
• Use both adapters to write a own application, testing Windows 10 operating system and MacOS (10.14.6)

Prologix adapter

The Prologix USB adapter can be programmed by sending commands through a serial terminal. The GPIB address of the device can be set by sending:

++addr #

So for example to set the GPIB address to ‘8’:

++addr 8

There several commands, which allows to configure the adapter to one needs. Also it’s possible to update the firmware.  To talk to the adapter FTDI device drivers are needed, which are available for Windows, Linux and MacOS.

The national Instruments (NI) GPIB-USB HS adapter

The NI adapter needs NI-VISA drivers to be installed. These drivers are available for Windows, Linux and MacOS.As far that I know there is no firmware available for these adapters. There is a lot of information about how to install NI-VISA drivers etc. The only thing I needed to was to install the NI-VISA software, and plug in the adapter.

Using existing application WinIQSIM

The application WinIQSIM works perfectly with the NI USB-GPIB-HS. The application has the benefit of using a GPIB device, or serial. However I could not get a serial device to work with my Rohde Schwarz AMIQ. I either received a timeout, or a communication error. At the end I tried to use a null modem cable, but this gives me problems also.

The main problem when using the Prologx in the case is the speed setting. The applications “sweeps” the baud-rate setting. The Prologix however, doesn’t care about serial baud setting. So the WinIQSIM application gets confused, when trying to determine the baud settings. I tried several options, even disabling the “sweep”, however the application kept trying to find the highest speed it could communicate on.

It might be possible to implement a driver in NI-VISA, I didn’t test this however.

In this case: The NI USB adapter wins.

Writing my own application

In this test I’m going to test the python script which I wrote to remotely control my HP 8175A. In this case I’m going to use Python since this makes testing under MacOS and Windows 10 very easy.

I’m going to use two modules:

• • PyVisa
  • PySerial

On both systems I’m using virtual environments.

Test under MacOS

And this test ended very quickly.. I tried to use PyVisa under MacOS, and couldn’t get PyVisa to work. The library isn’t listing my GPIB device. I tried installing several versions of NI-VISA library. I even tried different version of NI-488.2 drivers.

>>> import pyvisa >>> rm = pyvisa.ResourceManager() >>> rm.list_resources() ('ASRL/dev/cu.Bluetooth-Incoming-Port::INSTR', 'ASRL/dev/cu.EEsiPhone-WirelessiAPv2::INSTR') >>>

Update: I finally got the NI-VISA driver working under MacOS. I just reinstalled the drivers, and when I give the path to the library (I tried that before, which didn’t work) it works:

>>> import pyvisa
>>> rm = pyvisa.ResourceManager('/Library/Frameworks/VISA.framework/VISA')
>>> rm.list_resources()
('GPIB0::8::INSTR', 'GPIB0::9::INSTR')
>>>

When I use the NI-VISA tools, the adapter is recognized without problems.

Test under Windows 10

So I moved to windows, installed NI-VISA library, and PyVisa and it worked instantly. No problems what so ever.

Next I tried pySerial on both platforms, and both worked just fine. Of course I needed to adapt the device name (under MacOS this is:

ser = serial.Serial('/dev/cu.usbserial-PX4UALP2')

Under Windows this is:

ser = serial.Serial('COM4')

The whole python script:

import serial

cmd = ['RST','DM0;DUR0,1s;IFM(CLOCK),,,1111','DM1;CFM(CLOCK);TSA0;CHD0,(CLOCK),0000,0001,0010,0011,0100,0101,0110,0111,1000,1001;TSA9;CHD0,(END)','PM0;CD;(PROG1);CR7;CE;(END)','OM;POD 1','CM 0;CYM 1','UP;SA','LO']

ser = serial.Serial('/dev/cu.usbserial-PX4UALP2')

for c in cmd:
   send_cmd = c+'\n'
   ser.write(send_cmd.encode())

ser.close()