Author Topic: I Need Help With Choosing a Budget Oscilloscope!  (Read 5166 times)

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Offline Fungus

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #25 on: October 19, 2020, 12:21:01 am »
Real time display of logic signals is often not wanted anyway...you want to record and go back to study what happened in detail.

Imagine having to click record then stop then mouse around a bit every time you compile/run a program. It's a complete pain in the ass.

Sometimes you just need to see the signals.

 

Offline Fungus

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #26 on: October 19, 2020, 12:21:37 am »
@Fungus: please fix the quotation. I didn't write the text you attribute to me.

I guess we are now one and the same.  :-//

Yeah, there's no going back after three people have quoted it.
 

Offline battlecoder

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #27 on: October 19, 2020, 12:26:58 am »
I use mine for looking at Arduino pins. It's great to be able to put out pulses when you're debugging things.

I do the same, but I've rarely needed to check more than 2 channels at once. For digital signals it's usually "something" vs the clock. And if there's any jitter/timing issue, it's "normally"** a problem only if it messes things up in the digital domain, in which case a logic analyzer should help you see quickly that something is off.

** For most cases.

The problem is that those don't have a real time display of the signals. You have to press "record" and then go back and analyze.

(unless you have some software that I don't...)

I just got an Analog Discovery 2 and that does have real time display (16 digital channels, 2 analog). Maybe a 2-channel 'scope would be OK for me now.

.
Fair, but recording is normally a good thing when you are working with signals that change million times a second. Can't see myself debugging fast changing signals in realtime. I'd miss like half a million transitions just by blinking.

Also, thanks for reminding me that I wanted an Analog Discovery board at one point. Now I'll probably spend the rest of the night watching video reviews and trying *not* to start saving for one. Maybe if I start a diet of cheap instant noodles AND I can get everyone a cheaper Christmas present this year there might be a chance I can get one for myself before the year ends?  :-DD
 

Offline 0culus

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #28 on: October 19, 2020, 12:30:36 am »
Real time display of logic signals is often not wanted anyway...you want to record and go back to study what happened in detail.

Imagine having to click record then stop then mouse around a bit every time you compile/run a program. It's a complete pain in the ass.

Sometimes you just need to see the signals.

Sure, that's what the o-scope is for. The logic analyzer is a different instrument, and it works differently than an oscilloscope. Mine has a lot more memory depth available than most oscilloscopes too, as well as a fully configurable state machine trigger.
 

Offline battlecoder

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #29 on: October 19, 2020, 12:44:10 am »

Imagine having to click record then stop then mouse around a bit every time you compile/run a program. It's a complete pain in the ass.

Sometimes you just need to see the signals.

Sure, that's what the o-scope is for. The logic analyzer is a different instrument, and it works differently than an oscilloscope. Mine has a lot more memory depth available than most oscilloscopes too, as well as a fully configurable state machine trigger.

Definitely a different instrument, but one "common" use of >2 channels is debugging communication/logic signal errors, in which case I was saying that a logic analyzer is better suited.
There are definitely legitimate uses of 4 analog channels in an oscilloscope, but I don't think OP will miss having 4 channels as much as he/she thinks.
 

Offline Fungus

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #30 on: October 19, 2020, 01:24:41 am »
Also, thanks for reminding me that I wanted an Analog Discovery board at one point. Now I'll probably spend the rest of the night watching video reviews and trying *not* to start saving for one. Maybe if I start a diet of cheap instant noodles AND I can get everyone a cheaper Christmas present this year there might be a chance I can get one for myself before the year ends?  :-DD

There's a MASSIVE shortage of the chips at the moment so you'll be very lucky to get one this year. I only got mine by blagging my way through a special university education program.
 

Offline Fungus

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #31 on: October 19, 2020, 01:26:20 am »
There are definitely legitimate uses of 4 analog channels in an oscilloscope, but I don't think OP will miss having 4 channels as much as he/she thinks.

Depends on what you use it for. I use more than 2 channels very often, eg. for timing how long a function takes to execute, that sort of thing.
 

Offline ROFLCat

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #32 on: October 19, 2020, 02:07:51 pm »
If you can get by with just 2 channels maybe a SDS1202X-E can better suit your needs but might be at the top end of your budget.
At least it has some reasonable memory depth (14 Mpts), 7" display, better sensitivity than most others in this class and a suite of decoders.
[/quote]

Or there's the new 2-channel Rigol DS1052Z, which is even cheaper.

https://www.aliexpress.com/item/4001268857855.html
[/quote]

I had never heard of this model. Is it new or something?
 

Offline ROFLCat

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #33 on: October 19, 2020, 02:10:08 pm »
What about a GW Instek GDS-1000B Series? Since the OP has a GW Instek DMM maybe that brand is easier to find...

Actually, there is a GDS-1052U 50MHz, 2ch 'scope for about $340 second-hand, which I think is a bit too much.
 

Offline ROFLCat

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #34 on: October 19, 2020, 02:13:48 pm »
Anyway, I'll probably save up a bit for the DS1052E and 100% put on a hacked firmware. Too bad I can't afford a DS1054Z, the 2 extra channels could be pretty damn useful.

That's what I thought when I upgraded my oscilloscope a few years ago. Turns out I've only used channel 3 once. Channel 4 remains untouched :-DD. Bear in mind that enabling extra channels reduce your sampling rate and memory, so having more than 2 channels is not *that* great. For a bunch of logic signals (which is what I look at the most) a logic analyzer is more practical anyway. Even a cheap Saleae clone (which is what I have) works wonders.
[/quote]

Yes I'm aware of the reduction in sample rate on these mid-range 'scopes. Well you'll never know when you'll need them so... .
 

Offline ROFLCat

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #35 on: October 19, 2020, 02:21:13 pm »
There is this company that takes orders from China, especially TaoBao (Tmall.com). I'm a long-time customer of theirs and I have ordered some LR8 regulators through them; it was all fine, especially the price. The only problem was that they had told me it would take 3-4 months but my order took around 7 months to arrive. I think the major delay was because of the human malware that caused every shop and stuff to close down at the beginning of 2020, so I don't blame them.

I'll ask them and get a quote on the price and time on a DS1054Z, provided that Tmall has some for a good price.
 

Offline David Hess

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #36 on: October 19, 2020, 05:12:27 pm »
So I'm a 18 y/o EE who likes working with precision parts. I mostly design switchmode PSUs and precision low-noise voltage references for fun. Will be going to a university hopefully this year to study EE.

Neither require anything special in an oscilloscope.  Low noise would be nice for references however no modern oscilloscope is that low and a low noise amplifier allows the use of any oscilloscope.  An oscilloscope which can perform low frequency network analysis would be nice but this is not available in anything except high end instruments.

Storage is useful in general but not overwhelmingly so that I would exclude an old but working analog oscilloscope if it is inexpensive.

100 MHz of bandwidth or even 50 MHz is sufficient except for the highest performance switching regulators.

Do not underestimate the importance of probes.  A lower bandwidth oscilloscope with better probes, differential, current, whatever, will be more useful than a higher bandwidth oscilloscope without them.
 

Offline ROFLCat

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #37 on: October 19, 2020, 07:26:03 pm »
So I'm a 18 y/o EE who likes working with precision parts. I mostly design switchmode PSUs and precision low-noise voltage references for fun. Will be going to a university hopefully this year to study EE.

Neither require anything special in an oscilloscope.  Low noise would be nice for references however no modern oscilloscope is that low and a low noise amplifier allows the use of any oscilloscope.  An oscilloscope which can perform low frequency network analysis would be nice but this is not available in anything except high end instruments.

Storage is useful in general but not overwhelmingly so that I would exclude an old but working analog oscilloscope if it is inexpensive.

100 MHz of bandwidth or even 50 MHz is sufficient except for the highest performance switching regulators.

Do not underestimate the importance of probes.  A lower bandwidth oscilloscope with better probes, differential, current, whatever, will be more useful than a higher bandwidth oscilloscope without them.

Quite true. I've actually never used a proper oscilloscope so I don't know how much of a difference there is between 10kpts and 1Mpts of memory but I guess 10kpts would make waveforms look very inaccurate when measuring 0.1 to 10Hz noise.

I'll still be waiting for that company's response. If the total cost comes out less than about $370, I'll order a DS1054Z.
 

Offline David Hess

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #38 on: October 19, 2020, 10:33:06 pm »
Quite true. I've actually never used a proper oscilloscope so I don't know how much of a difference there is between 10kpts and 1Mpts of memory but I guess 10kpts would make waveforms look very inaccurate when measuring 0.1 to 10Hz noise.

The problem is that the impedance buffer stage at the input of the oscilloscope has quite poor low frequency noise with a high flicker noise corner frequency.  It is just a compromise to be made for high bandwidth and fast recovery from overload.  Oscilloscope front ends designed for low noise have a much more limited bandwidth.

But noise is not a problem when you can easily build an external low noise amplifier.

Limited record length creates more aliasing of high frequency noise to low.  So for instance 10 kpoints from 0.1 to 10Hz has a sample rate of 1kHz so input bandwidth needs to be limited to below 500Hz.  A 1 Mpoint record length considerably relaxes this requirement.

I do not have any DSOs suitable for FFT noise measurement so I still rely on spot noise measurements using the oscilloscope to measure RMS noise.  In practice spot noise is usually more relevant anyway, like measuring total noise from 0.1 to 10 Hz.  You can bet that if I ever design a DSO, it will include this capability and network analysis as well.
 

Offline james_s

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #39 on: October 20, 2020, 12:58:13 am »
It really depends on what you're trying to do. The scope I use the most is a TDS3000 with 10k points and in most cases I have not found that to be a major limitation. I have a TDS700 with the 8M points option and I very rarely make use of that extra memory depth because it just results in capturing a ton of excess waveform to scroll through and it slows down the interface when you have a really big capture. IMHO it's better to focus on setting up the triggering to capture what you want instead of using massive amounts of memory to capture everything.
 
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Online tautech

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #40 on: October 20, 2020, 01:25:56 am »
It really depends on what you're trying to do. The scope I use the most is a TDS3000 with 10k points and in most cases I have not found that to be a major limitation. I have a TDS700 with the 8M points option and I very rarely make use of that extra memory depth because it just results in capturing a ton of excess waveform to scroll through and it slows down the interface when you have a really big capture. IMHO it's better to focus on setting up the triggering to capture what you want instead of using massive amounts of memory to capture everything.
Quite so however it much depends on your use case as one channel might be triggered on to capture an event while other channels might be monitoring so to find what might have caused such an event.
Of course success depends on how time correlated the channels and events actually are, timebase settings and the mem depth available.
When working like this there is never too much mem depth.
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Online nctnico

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #41 on: October 20, 2020, 06:20:36 am »
It really depends on what you're trying to do. The scope I use the most is a TDS3000 with 10k points and in most cases I have not found that to be a major limitation. I have a TDS700 with the 8M points option and I very rarely make use of that extra memory depth because it just results in capturing a ton of excess waveform to scroll through and it slows down the interface when you have a really big capture. IMHO it's better to focus on setting up the triggering to capture what you want instead of using massive amounts of memory to capture everything.
No. Use an oscilloscope with a faster hardware platform. Those TDS700 are rather slow to drive (been there, done that). Modern oscilloscopes have no problem dealing with tens of megapoints worth of data.
« Last Edit: October 20, 2020, 06:22:31 am by nctnico »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline ROFLCat

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #42 on: October 20, 2020, 03:13:56 pm »
The problem is that the impedance buffer stage at the input of the oscilloscope has quite poor low frequency noise with a high flicker noise corner frequency.  It is just a compromise to be made for high bandwidth and fast recovery from overload.  Oscilloscope front ends designed for low noise have a much more limited bandwidth.

Interesting. Didn't know about that. But then again, I want some rough measurements on the noise of precision parts and being able to debug my power supplies and take output ripple measurements is really good. One other reason I want a decent digital oscilloscope is the ability to decode I²C and SPI signals as I'm also into data acquisition.
 

Offline ROFLCat

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #43 on: October 20, 2020, 03:21:34 pm »
Thankfully, there's a deflation happening and the Rials per US Dollars ratio dropped by about 10% today which is great. The chances of getting a DS1054Z increases. :D

Also, if I there's a bit of money left in my pocket after an oscilloscope, I'll get this very unique and extremely rare frequency counter from a reputable and old manufacturer of test equipments. Stay tuned? ;D
Let's just say that it has a unique display with an affordable price.
 

Offline David Hess

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #44 on: October 20, 2020, 07:25:23 pm »
The problem is that the impedance buffer stage at the input of the oscilloscope has quite poor low frequency noise with a high flicker noise corner frequency.  It is just a compromise to be made for high bandwidth and fast recovery from overload.  Oscilloscope front ends designed for low noise have a much more limited bandwidth.

Interesting. Didn't know about that. But then again, I want some rough measurements on the noise of precision parts and being able to debug my power supplies and take output ripple measurements is really good. One other reason I want a decent digital oscilloscope is the ability to decode I²C and SPI signals as I'm also into data acquisition.

It is not a big deal; it just means do not look to oscilloscopes for low noise measurements unless you want to deal with something like a Tektronix 7A22.  Designing and building a low noise preamplifier to test reference and regulator noise is not difficult and then any oscilloscope can be used.
'
 

Online tautech

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #45 on: October 20, 2020, 08:53:08 pm »
But then again, I want some rough measurements on the noise of precision parts and being able to debug my power supplies and take output ripple measurements is really good. One other reason I want a decent digital oscilloscope is the ability to decode I²C and SPI signals as I'm also into data acquisition.
How good will you require ?
As we mainly use a scope with 10x probes a scopes max sensitivity can limit how far down we can go without switching to a 1x probe.
Study of scope datasheets and marketing blurb might reveal some brands are better suited down in the mV/div region due to high sensitivity and lower noise inputs.
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Offline ROFLCat

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #46 on: October 21, 2020, 05:01:07 am »
The problem is that the impedance buffer stage at the input of the oscilloscope has quite poor low frequency noise with a high flicker noise corner frequency.  It is just a compromise to be made for high bandwidth and fast recovery from overload.  Oscilloscope front ends designed for low noise have a much more limited bandwidth.

Interesting. Didn't know about that. But then again, I want some rough measurements on the noise of precision parts and being able to debug my power supplies and take output ripple measurements is really good. One other reason I want a decent digital oscilloscope is the ability to decode I²C and SPI signals as I'm also into data acquisition.

It is not a big deal; it just means do not look to oscilloscopes for low noise measurements unless you want to deal with something like a Tektronix 7A22.  Designing and building a low noise preamplifier to test reference and regulator noise is not difficult and then any oscilloscope can be used.
'

Oh yeah I'm trying to build a cascaded Sallen-Key low-pass filter based on two LTC2055s (the lowest noise op amps that I can find and purchase). I might buy more in the future and connect them in parallel to achieve even lower noise?
 

Offline ROFLCat

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #47 on: October 21, 2020, 05:09:57 am »
But then again, I want some rough measurements on the noise of precision parts and being able to debug my power supplies and take output ripple measurements is really good. One other reason I want a decent digital oscilloscope is the ability to decode I²C and SPI signals as I'm also into data acquisition.
How good will you require ?
As we mainly use a scope with 10x probes a scopes max sensitivity can limit how far down we can go without switching to a 1x probe.
Study of scope datasheets and marketing blurb might reveal some brands are better suited down in the mV/div region due to high sensitivity and lower noise inputs.

Well, power supply noise and ripples are usually taken with a 20MHz bandwidth limit so that's completely fine on the 1x setting. Decoding I²C and SPI buses is fine with a 10x too since they're logic level and 3.3Vpp or 5Vpp.
And about the low-noise references, I'll be using a low-noise amplifier to boost up the signal by a factor of 10 or 100 as reading microvolts isn't too easily with any oscilloscope. ;D
Bandwidth on these measurements is irrelevant to be honest as it will mostly likely be low-frequency stuff (0.1 to 10Hz).
 

Offline Fungus

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #48 on: October 21, 2020, 05:43:18 am »
And about the low-noise references, I'll be using a low-noise amplifier to boost up the signal by a factor of 10 or 100 as reading microvolts isn't too easily with any oscilloscope. ;D

Yep.

There's people here who'll go on and on about how their brand of oscilloscope can do 0.5mV instead of 1mV but is that really a make/break difference when a cheapo amplifier can let you see 1uV noise on any oscilloscope?
 

Offline David Hess

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #49 on: October 21, 2020, 09:10:04 am »
Oh yeah I'm trying to build a cascaded Sallen-Key low-pass filter based on two LTC2055s (the lowest noise op amps that I can find and purchase). I might buy more in the future and connect them in parallel to achieve even lower noise?

Usually the problem is removing the DC component while passing frequencies down to 0.1 Hz.  Low noise and low drift with a 0.1 Hz low frequency cutoff is somewhat contradictory because of the impedances required to get such a long time constant with a reasonable value of capacitance.  Check out Linear Technology application notes 83 and 124 for example circuits.

Another method is to use an "offset probe" or differential comparator which subtracts the DC voltage.  This is essentially a differential probe with one input connected to the source to measure and the other connected to a low noise reference of the same voltage.
 


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