VOGONS


First post, by Hamby

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I was just watching a YouTube video on Adrian's Digital Basement's channel, and in this episode he forewent his $3k oscilloscope and $350 multimeter and substituted comparatively cheap tools.
Obviously the "cheap" tools ($60 oscilloscope and $25 multimeter) weren't as capable as his expensive ones, but they got the job done.
I think this video will build confidence in less-experienced and less-skilled retro enthusiasts who want their vintage technology to work, but don't have the training or skills of professionals or serious electronics hobbyists (those more into the electrical engineering side of things rather than the vintage side).

Anyway, I felt I had to share it here, because I'm confident I'm not the only one who A) wants to make/keep his retro toys working and B) would like to get retro toys that need a little TLC.
https://www.youtube.com/watch?v=PyFeBAcg7ls

Reply 1 of 12, by BitWrangler

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One caveat though with the cheaper stuff, don't trust it's maximum current and voltage ratings.

Apart from that, I'm a believer in "just enough to get the job done". Also I'd rather see a (the same) weird reading on two different cheapie meters than a single really expensive one. By weird I mean, way off what you'd get if it was working right, but also way off what you'd expect if it was broken the way you were thinking it was broken. So if you've got the harbor freight cheapie and the beat up old micronta cheapie saying more or less the same thing, you get to figuring out how the heck that could happen on the board... if you've got the single spendier meter, you start wondering what the heck could have happened to your precious $350 meter....

Unicorn herding operations are proceeding, but all the totes of hens teeth and barrels of rocking horse poop give them plenty of hiding spots.

Reply 2 of 12, by stamasd

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With only a little more money, you can get a scope that's actually useful for PC stuff (60-70MHz bandwidth, mine was about $120).

I/O, I/O,
It's off to disk I go,
With a bit and a byte
And a read and a write,
I/O, I/O

Reply 3 of 12, by TrashPanda

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stamasd wrote on 2022-02-12, 23:35:

With only a little more money, you can get a scope that's actually useful for PC stuff (60-70MHz bandwidth, mine was about $120).

I too think the middle ground is the best place to be, it’s not horribly expensive but not nasty cheap either.

Oh noes, the cap let the shmooo out 😁

Reply 4 of 12, by Hamby

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stamasd wrote on 2022-02-12, 23:35:

With only a little more money, you can get a scope that's actually useful for PC stuff (60-70MHz bandwidth, mine was about $120).

Can you suggest one? I don't know anything about oscilloscopes, but I'd like to learn.

Reply 5 of 12, by TrashPanda

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If you don’t mind listening to a crazy Aussie you should look up Dave from EEvBlog on YouTube, he has a ton of vids on scopes.

He is also a great watch.

Another fun channel to watch would be Electroboom, lots of scope work there too.

These are channels that might give you a look into what scopes can do and how they are used for troubleshooting.

Last edited by TrashPanda on 2022-02-13, 01:04. Edited 1 time in total.

Oh noes, the cap let the shmooo out 😁

Reply 6 of 12, by stamasd

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Hamby wrote on 2022-02-12, 23:52:

Can you suggest one? I don't know anything about oscilloscopes, but I'd like to learn.

Mine is an Instrustar ISDS 220B (the B means it also has a DDS signal generator, programmable up to 20MHz). It works fine. http://english.instrustar.com/product_detail.asp?nid=1584

I also have a very old analog oscilloscope, Hitachi V665 made in the 1970s. This one I picked on ebay a few years ago for about $70 and it also works great. It also has a bandwidth of approx 60MHz. You can still find the manual online https://www.allaboutcircuits.com/test-measure … -v-665a/manual/ Here's a YT video about this one (no it's not my video) https://www.youtube.com/watch?v=JzrLXAQ4Dh4

I/O, I/O,
It's off to disk I go,
With a bit and a byte
And a read and a write,
I/O, I/O

Reply 7 of 12, by pentiumspeed

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Extremely cheap is not what you to want live with. Like 25 dollar thing.

Moderate cheap or reasonable cost is worth having the stuff.

Cheers,

Great Northern aka Canada.

Reply 8 of 12, by rasz_pl

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BitWrangler wrote on 2022-02-12, 23:25:

Apart from that, I'm a believer in "just enough to get the job done". Also I'd rather see a (the same) weird reading on two different cheapie meters than a single really expensive one.

whole point of expensive meter is confidence, you dont need a second look = saved time

BitWrangler wrote on 2022-02-12, 23:25:

you start wondering what the heck could have happened to your precious $350 meter....

you dont, because being expensive doesnt make it precious, it makes it dependable. Its just a tool in a shop full of tools.

This turns out to not even be a 48MHz scope after all, but ~10MHz before it starts glitching 🙁 not so hot anymore. You will be seeing more aliasing than real signals.

Reply 9 of 12, by mkarcher

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rasz_pl wrote on 2022-02-13, 06:31:

This turns out to not even be a 48MHz scope after all, but ~10MHz before it starts glitching 🙁 not so hot anymore. You will be seeing more aliasing than real signals.

If you want to use the cheap stuff, you really have to read (and be able to understand the details of) the fine print completely. The device Adrian showed never was advertised as a scope with 48MHz bandwidth at all, but just as a digital scope with 48MHz sample rate, with an analog bandwidth of just 20MHz. The sample rate of 48MHz makes it completely useless for anything exceeding 24MHz (because those signals will be aliased to fake signals below 24MHz), and if the analog bandwidth of 20MHz is true (no reason to doubt that, building a 20MHz analog frontend is very cheap and easy nowadays), it most likely doesn't do a good job of removing all components exceeding 24MHz (passing everything up to 20MHz, but sufficiently blocking 24MHz is a quite complicated and expensive thing). Another rule of thumb is that depending on your requirements on fidelity, the sample rate needs to be 3 times ("well, I just want to get an estimate of the amplitude and see whether there are hickups in the clock") to 10 times ("I want to see whether the rise time of the suspected square wave matches the specs") the maximum signal rate, so you get down to 4.8 to 16MHz maximum usable frequency.

Thus, an experienced electronics engineer can tell directly from the banner specs that a "cheap 20 MHz bandwidth, 48MHz sample rate" digital oscilloscope is generally useful up to 5 MHz, might be good enough up to 10MHz, but is very likely completely useless above 15MHz (due to unavoidable aliasing of not suffiently suppressed harmonics). It's a pity that the specs are chosen (most likely intentionally) to generate the impression that the device is useful up to 20MHz, which is next to impossible at that price point with a sample rate of 48MHz. Of course, with proper sample-and-hold, equivalent time sampling and extremely precise trigger circuits, you could get a decent 20MHz signal representation at a sample rate of 48MHz, but this requires expensive analog electronics, expensive precise timing and sophisticated analysis software and still is only usable for perfectly periodic signals. In fact, that's exactly how the expensive brands did it successfullly like 30 to 40 years ago when 48MHz sample rate was the best you could get for any kind of money, but there still is no way to fit that in a USD 60 device.

My impression of the presentation of that device is: The hardware delivers what an expert could expect, although a less experienced person might expect more. On the other hand, the software looks like a least-effort solution to show that the hardware works, with some "buzzword features" like the sin x/x interpolation (which in my oppinion is actually more sensible and useful than Adrian considers it, at least if the device had proper anti-aliasing filters). Possibly there are some hidden gems in the software Adrian didn't detect (like it could do intensity grading at high sample rates, which would make the brightness control useful), or it does keep some kind of reference point when changing the timebase, but that reference point was accidentally off-screen. The software didn't make that impression, though. As I expect the hardware to just do dumb streaming of one 48MB/s stream (I wouldn't be surprised if the sample rate drops to 24MHz in two-channel mode), the awful triggering behaviour is caused by the software. Possibly the software behaves better in "normal" than in "auto" triggering mode, so the software might be more usable in a different setup, but on the other hand, full-blown scopes have no problems triggering the signals Adrian used in "auto" mode.

Reply 10 of 12, by rasz_pl

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mkarcher wrote on 2022-02-13, 09:21:

The device Adrian showed never was advertised as a scope with 48MHz bandwidth at all, but just as a digital scope with 48MHz sample rate, with an analog bandwidth of just 20MHz.

Adrian himself has trouble fully understanding sampling theorem https://youtu.be/8ts5J09Y7Gc?t=1380 or at least articulating it. "top and bottom, terrible sounding" audiophoolery full steam ahead.

mkarcher wrote on 2022-02-13, 09:21:

The sample rate of 48MHz makes it completely useless for anything exceeding 24MHz (because those signals will be aliased to fake signals below 24MHz), and if the analog bandwidth of 20MHz is true (no reason to doubt that, building a 20MHz analog frontend is very cheap and easy nowadays), it most likely doesn't do a good job of removing all components exceeding 24MHz (passing everything up to 20MHz, but sufficiently blocking 24MHz is a quite complicated and expensive thing).

For scopes listed BW is not a cutoff but a 3 DB drop, etched in stone as an ieee norm.

mkarcher wrote on 2022-02-13, 09:21:

Another rule of thumb is that depending on your requirements on fidelity, the sample rate needs to be 3 times ("well, I just want to get an estimate of the amplitude and see whether there are hickups in the clock") to 10 times ("I want to see whether the rise time of the suspected square wave matches the specs") the maximum signal rate, so you get down to 4.8 to 16MHz maximum usable frequency.

Due to slow filter roll-off and potential for aliasing, if you have good anti alias filter and flat frequency response close to nyquist is fine. This listed 20MHz analog BW figure is most likely just a measured property of poorly "designed" analog front end consisting of a trimmer cap, two poly fuses and CD4051 switching in attenuation. Without proper anti-aliasing filter everything on the screen is garbage, especially if you are forced to start using sample rates below >2x natural filtering of the front end.

mkarcher wrote on 2022-02-13, 09:21:

Thus, an experienced electronics engineer can tell directly from the banner specs that a "cheap 20 MHz bandwidth, 48MHz sample rate" digital oscilloscope is generally useful up to 5 MHz, might be good enough up to 10MHz, but is very likely completely useless above 15MHz (due to unavoidable aliasing of not suffiently suppressed harmonics).

Hey, its like you read my YT comment from 6 days ago under Adrians video 😀

mkarcher wrote on 2022-02-13, 09:21:

My impression of the presentation of that device is: The hardware delivers what an expert could expect

would you expect glitching at rated sample rate that only goes away after going down to <4x lower frequency?

17 years ago!! there was this thing called USBee AX https://www.usbee.com/axmanual.pdf https://www.interworldna.com/cwave/index.php pretty similar BOM and schematic, same Cypress FX2LP bridge, 8bit DAC, genuine opamps in the front end. Sample rate of 16Msps and realistic BW limited to 3MHz in order to be actually useful.

mkarcher wrote on 2022-02-13, 09:21:

As I expect the hardware to just do dumb streaming of one 48MB/s stream (I wouldn't be surprised if the sample rate drops to 24MHz in two-channel mode), the awful triggering behaviour is caused by the software.

in the second video Adrian switched software, glitching persisted above 10MHz. Considering over 15 year old product did better something is wrong with hardware design of Hantek. My guess is using overclocked ~5MHz ADC as is typical in Chinese products. Quick google found example of "100MHz" Hantek DSO-2090 using ADC08060.

Reply 11 of 12, by mkarcher

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rasz_pl wrote on 2022-02-13, 11:08:

Adrian himself has trouble fully understanding sampling theorem https://youtu.be/8ts5J09Y7Gc?t=1380 or at least articulating it. "top and bottom, terrible sounding" audiophoolery full steam ahead.

Adrian's limited understanding of the sampling theorem is also supported by his oppinion on the sinx/x reconstruction method. On the other hand: If you don't have a proper reconstruction low-pass (i.e. a filter that removes alias frequencies introduced in the DAC), you will actually get those dreaded terrible sounding staircase-like signals. The sampling theorem doesn't say: "If you reproduce a sampled signal, you get a bandwidth-limited signal the perfectly reconstructs the original bandwidth-limited signal" (even if the original signal was perfectly bandwith limited before sampling). Instead, it just says "there is only one bandwith-limited signal signal that matches these samples. If you somehow manage to create a bandwidth-limited signal that hits all the samples, you get back the original bandwidth-limited signal." The sampling theorem doesn't help at all in how to reconstruct a bandwidth limited signal.

And guess what: A lot of sound cards with variable rate playback do not have variable roll-off low-pass filters on the output. I was very surprised as teen when a friend told me: "22kHz sounds better than 11kHz" by starting with a 11kHz wave file of an electronic phone ring tone, which sounded very harsh when played back through his AD1848-based sound card. He then used the sample rate converter built into Windows 95 to upsample the file to 22kHz, and played it back again, which provided a considerably cleaner sound. Obviously, Windows did a better job of removing aliases when upsampling than the analog filtering on the soundcard did.

rasz_pl wrote on 2022-02-13, 11:08:
mkarcher wrote on 2022-02-13, 09:21:

The sample rate of 48MHz makes it completely useless for anything exceeding 24MHz (because those signals will be aliased to fake signals below 24MHz), and if the analog bandwidth of 20MHz is true (no reason to doubt that, building a 20MHz analog frontend is very cheap and easy nowadays), it most likely doesn't do a good job of removing all components exceeding 24MHz (passing everything up to 20MHz, but sufficiently blocking 24MHz is a quite complicated and expensive thing).

For scopes listed BW is not a cutoff but a 3 DB drop, etched in stone as an ieee norm.

Indeed. But AFAIK, the norm doesn't require a specific steepness of the input low-pass (whether it's an intentional low-pass or just inherent in the scope design). A 6db/octave-like behaviour (aka first order lowpass) is common, but steeper roll-offs are possible, and are sorely needed if the -3dB point is so close to the nyquist frequency. I have one of those 1Gs/s scopes with the cheap 60MHz frontend bandwith limit, and I am indeed able to measure the frequency of a 125MHz signal, but I wouldn't trust the indicated amplitude or curve shape in any way. This shows that slow roll-off is quite common in scope frontends (and with nyquist being at 500MHz, it's not a problem at all).

rasz_pl wrote on 2022-02-13, 11:08:
mkarcher wrote on 2022-02-13, 09:21:

Another rule of thumb is that depending on your requirements on fidelity, the sample rate needs to be 3 times ("well, I just want to get an estimate of the amplitude and see whether there are hickups in the clock") to 10 times ("I want to see whether the rise time of the suspected square wave matches the specs") the maximum signal rate, so you get down to 4.8 to 16MHz maximum usable frequency.

Due to slow filter roll-off and potential for aliasing, if you have good anti alias filter and flat frequency response close to nyquist is fine. This listed 20MHz analog BW figure is most likely just a measured property of poorly "designed" analog front end consisting of a trimmer cap, two poly fuses and CD4051 switching in attenuation. Without proper anti-aliasing filter everything on the screen is garbage, especially if you are forced to start using sample rates below >2x natural filtering of the front end.

To be fair, "proper anti-aliasing" at lower sample rates is something even the big brands of scope manufacturers get wrong. Adrian alluded to an old Tektronix series of digital scopes, most likely the TDS-210 / TDS-220 series. If you slow down the time base, the screen starts to show the textbook example of aliasing without any dampening/filtering. If you look a 1Vpp 1.001 MHz signal at a timebase slow enough that the scope runs at 50kHz sample rate, you will see a 1kHz sine wave at the full 1Vpp (I observed that first-hand in a physics lab). Newer digital scopes are better in this regard, for one by offering a min/max mode where it doesn't just show a single sample taken at a very short point in time, but actually the minimum and maximum during the interval of a pixel or even the intensity-graded stuff (with marketing names like "megaZoom" or "Digital Phosphor Oscilloscope"). I fully agree with you on how the frontend is likely to look. The cap (why a trimmer at all? Is anyone gonna complain if the -3dB point is at 22MHz or 19.5MHz?) and the 1MOhm input impedance make a first-order lowpass, and that's it. You just don't get a better frontend at that price point.

rasz_pl wrote on 2022-02-13, 11:08:
mkarcher wrote on 2022-02-13, 09:21:

Thus, an experienced electronics engineer can tell directly from the banner specs that a "cheap 20 MHz bandwidth, 48MHz sample rate" digital oscilloscope is generally useful up to 5 MHz, might be good enough up to 10MHz, but is very likely completely useless above 15MHz (due to unavoidable aliasing of not suffiently suppressed harmonics).

Hey, its like you read my YT comment from 6 days ago under Adrians video 😀

In fact, I didn't. It's just an indicator that we either joined the same school of thought or there is some general truth to it.

rasz_pl wrote on 2022-02-13, 11:08:
mkarcher wrote on 2022-02-13, 09:21:

My impression of the presentation of that device is: The hardware delivers what an expert could expect

would you expect glitching at rated sample rate that only goes away after going down to <4x lower frequency?

17 years ago!! there was this thing called USBee AX pretty similar BOM and schematic, same Cypress FX2LP bridge, 8bit DAC, genuine opamps in the front end. Sample rate of 16Msps and realistic BW limited to 3MHz in order to be actually useful. [... ] Considering over 15 year old product did better something is wrong with hardware design of Hantek. My guess is using overclocked ~5MHz ADC as is typical in Chinese products.

Hmm, talking about op-amps. I guess Adrians device will have some moderately high-frequency op-amp in the frontend, too. Otherwise, you won't get below something like a 0.1v/div scale. I can't imagine the DAC having more than 8 bits, so at a typical reference voltage of 2.5V, you will get 10mV/step (give or take a factor of 2 for bipolarity, for a 1.25V voltage). This would be 10 steps per division at 0.1V/div, making 0.05V/div with just 5 steps/div borderline and 0.02V/div completely useless.

No, I don't expect glitching at the rated sample rate. I didn't watch the second video at that time and attributed the glitches just to the software not being up to the job. The OpenHantek software on the other hand shows clearly that at 48MS/s the USB streaming to Adrian's computer is unreliable. Getting stable software triggering when there are missing chunks in the stream is impossible, of course. I don't think the glitch issue is due to the ADC being overclocked (which is still very much possible), but on the digital side (e.g. firmware, relying on specific USB host chip timing or bad USB signal integrity causing lost frames)

Reply 12 of 12, by rasz_pl

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mkarcher wrote on 2022-02-13, 19:40:

No, I don't expect glitching at the rated sample rate. I didn't watch the second video at that time and attributed the glitches just to the software not being up to the job. The OpenHantek software on the other hand shows clearly that at 48MS/s the USB streaming to Adrian's computer is unreliable. Getting stable software triggering when there are missing chunks in the stream is impossible, of course. I don't think the glitch issue is due to the ADC being overclocked (which is still very much possible), but on the digital side (e.g. firmware, relying on specific USB host chip timing or bad USB signal integrity causing lost frames)

logic analyzers based on same cypress chip are rock solid at 24MHz. According to Cypress bulk streaming transfers are reliable to at least 39 MB/s. I havent heard of a single case of someone having trouble above 10MHz. OpenHantek6022 outright disables 48MHz, but 30 and 24 should work fine.

Apparently https://www.eevblog.com/forum/testgear/hantek … ope-review-ish/ is using proper 40MHz AD9288, $7 from legitimate sourced in bulk, and four $2.5 AD8065 opams. Half the BOM right here unless someone employed creative parts substitution. https://sigrok.org/wiki/Hantek_6022BL documents using a fly by night ADC clone by MXTronix MXT2088
frontend of this thing https://github.com/Ho-Ro/Hantek6022API/tree/main/hardware

Over at eevblog user Rick Law actually bothered to test it https://www.eevblog.com/forum/testgear/hantek … 2007/#msg232007
other than noise and obvious limitations it worked fine for him. In my YT comment I was guessing 150ns rise time signals being the limit, looks like I was pretty close.

megathread https://www.eevblog.com/forum/testgear/hantek … -20mhz-usb-dso/

Seems Adrian has bad unit or USB issues.