Alternatives to the Velleman PCSGU250 (discontinued) ?

[timtam]

It looks like the Velleman PCSGU250 that has been commonly used around here for pickup bode plots has been discontinued. Velleman are not showing any replacement. Sources like ebay show a few PCSGU250 for sale, but at higher prices.
www.velleman.eu/products/view/?id=377622

Has anyone tried any of the small number of other inexpensive 2-channel USB-based oscilloscope/signal generator combinations, that can be set up to do an automated frequency sweep and generate the output for a bode plot ?

The specs of the Picoscope 2204A appear to make it a possible candidate, as they look similar to the PCSGU250, eg 8-bit voltage resolution (the 2204A lists 8-bits but also claims 12-bit 'enhanced' resolution). The 2204A is part of a suite of Pico USB-based oscilloscopes ranging up to several-thousand dollar devices with lots of pro features. The free Picoscope software is similar across the whole range. A slightly cheaper version pf the 2204A without probes is available (2204A-D2). The price is about half what some vendors are asking for the remaining PCSGU250's. It is carried by most of the major electronics retailers (Farnell, Mouser etc) as well as direct from Pico on Amazon.
www.picotech.com/oscilloscope/2000/picoscope-2000-specifications
www.picotech.com/download/datasheets/picoscope-2203-2204-2205-datasheet.pdf
www.farnell.com/datasheets/3705645.pdf

The software to do automated bode plots is a free addon (FRA Frequency Response Analysis) and appears to be well-supported ...

www.picotech.com/library/picoapp/frequency-response-analyzer-with-bode-plots

bitbucket.org/hexamer/fra4picoscope/wiki/Home

www.picotech.com/download/brochures/frequency-response-analyzer-application-note.pdf

Some Picoscope videos ...

Bode plot app, using 2204A Picoscope

Bode plot using older version of same app with 5000-series Picoscope

Another way of doing real-time frequency response in the standard software

 

Ditto

There are also Matlab, Python and Labview tools to interface with the Picoscope, eg
www.mathworks.com/matlabcentral/fileexchange/?q=profileid:3052752

Picking the relevant values off the bode plot (resonant frequency etc) appears possible via the 2 available cursors in the FRA app. The -3dB frequency is measured automatically. The data can also be exported, eg to Excel - that would enable some additional options, like automatic Q factor calculation (assuming we agreed on a definition). Export would appear to be necessary for comparing two or more bode plots on the same chart.

[antigua]

It blows my mind that there still aren't many USB oscilloscope options, let alone ones with bode plotting built in. Searching for "usb oscilloscope" and "bode plot" or "response curve" or "network analyzer", and some new stuff comes up, but it seems to generally be more expensive and not even as useful as what we had in the Velleman. The Syscomp CGR-101 was pretty good too for the price point, but they also stopped producing that.

Aside from the Velleman and Syscomp, I've also tried using the Digilent Analog Discovery with the WaveForms software   www.amazon.com/Analog-Discovery-Systems-Kit-Oscilloscope/dp/B07G8LG3JX/ref=sr_1_4?crid=WAE73A14ZRHJ&keywords=analog+discovery&qid=1695193508&s=industrial&sprefix=analog+discovery%2Cindustrial%2C123&sr=1-4&ufe=app_do%3Aamzn1.fos.c3015c4a-46bb-44b9-81a4-dc28e6d374b3  , and that is a really high quality hardware and software pair, but it was less useful to me, just because the Velleman software seemed almost purpose built for doing quick and dirty overlapping plots and labelling on the fly, so I could test lots of pickups in not a lot of time. The WaveForms software is very powerful and it can even do the response curve integration mathematically, but there's a learning curve to it, and it still not quite as convenient as the Velleman software was.

I think with this and other USB oscilloscopes, it's going to be necessary to export the data, maybe a CSV, into Excel and manually graph the results. I'm thinking I might make a simple Javascript interface to allow several plot's worth of data to pasted in, and then presented with the Google Charts API and allow for some labelling, because what we really want to do most of time is compare two or more pickups, or compare the outcome after tweaking a pickup or a circuit. 

A few people use the Rightmark audio software and then test the pickups with their computer sound card. As far as I know, that works well and is potentially free, but since the Velleman worked so well for me, I didn't use that method. I think you have to wait a minute or two for it to perform the sweep, and then only after you can see what the outcome was, that process made it harder for me to correct errors in the test setup.

There have been the Hantek and Picoscope USB oscilloscopes on the market for a few years and are still available, but they don't seem to have very full feature bode plot support in the software. I'm sure they offer a data export feature, which is probably the most I can hope for from these devices going forward.

[ms]

If you think you need to move to a device that does not do the data analysis for you, one thing to consider is moving to a different type of hardware.  Relative to the requirements of pickup analysis, the USB digital scope has too few bits in the quantization, but samples a lot faster than necessary.  It is OK with the integrator circuit, and it is convenient if it does the analysis (plotting, etc.) for you with an integrated software package.  It that is no longer available, then you could change to a device with a lots more bits.  Recording interfaces typically sample up to 192 KHz, plenty fast enough, and have really good digitizers.  You need a software package for data taking; I think most people would prefer Octavia (the free Matlab replacement).

[timtam]

Yes I was a tad surprised with the (low) 8-bit spec of the Velleman and the Picoscope 2204A when I saw it. On the other hand it's often much easier to optimize the volts/bit with gain (range) settings in a digital oscilloscope than it is with most ADC boards I've worked with (which instead tend to have 12 or 16 bit sampling). The "enhanced" resolution with the 2204A does gain a few extra bits by over-sampling ....

www.picotech.com/library/oscilloscopes/resolution-enhancement

My experience with interfacing to hardware is mostly with (expensive) Matlab. Not sure if (free) Octave can use the same drivers/APIs ?

[ms]

Sept 20, 2023 22:35:34 GMT -5 timtam said:

Yes I was a tad surprised with the (low) 8-bit spec of the Velleman and the Picoscope 2204A when I saw it. On the other hand it's often much easier to optimize the volts/bit with gain (range) settings in a digital oscilloscope than it is with most ADC boards I've worked with (which instead tend to have 12 or 16 bit sampling). The "enhanced" resolution with the 2204A does gain a few extra bits by over-sampling ....

www.picotech.com/library/oscilloscopes/resolution-enhancement

My experience with interfacing to hardware is mostly with (expensive) Matlab. Not sure if (free) Octave can use the same drivers/APIs ?

I think Octave uses the same drivers, but I do not know.  (I use Python, which I realize is not the choice most people make.)

Picoscope: "For this technique to work, the signal must contain a very small amount of Gaussian noise, but for practical applications this is generally provided by the scope itself and the noise inherent in normal signals."  This reads like something out of the 1980s.  You get 24 bits at 192 KHz in a current recording interface.  Sure, the lowest order bits are not perfect, but that is not important when you have so many.