Author Topic: I Need Help With Choosing a Budget Oscilloscope!  (Read 5637 times)

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Offline battlecoder

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #50 on: October 21, 2020, 08:07:23 pm »
Check out Linear Technology application notes 83 and 124 for example circuits.

^This. Application notes are gold mines of good advise and practical uses of different components and technologies. On the topic of low-noise amplifiers for instance there's this guy who built a reasonable amplifier circuit based on a couple of application notes:


AND he builds the device to characterize low-noise regulators and power supplies, so it might be well in line with OP's request.

Even more, the guy is actually using a 70Mhz Hantek DSO5072P scope (which is a model someone here already suggested) and seems to work just fine for the job.

I think brands like Hantek/Mustool/Owon/whoever-the-original-oem-of-those-devices-is are doing a pretty good job at making decent entry-level oscilloscopes that are WAY beyond the specs of what hobbyist had access to even 10 years ago. They are definitely not state of the art, but I would have killed for one of those scopes when I started. Some of them are terrible, sure, but we are starting to see some models that definitely meet the specs, have a reasonable range of features, and don't have that many UX glitches as previous "budget" scopes.

Now, sure, if you can afford a Rigol or a Siglent ( or if you happen to find a good deal for a second hand <reputable brand>) by all means go for it. Just don't overlook the few little gems that are coming from "generic" manufacturers. I've seen a lot of people doing amazing stuff with them already.
 

Offline Fungus

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #51 on: October 22, 2020, 11:52:14 am »
You can buy a pre-built signal amplifier on Aliexpress for $5 and add a battery and biscuit tin.
 

Offline ROFLCat

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #52 on: October 25, 2020, 08:11:11 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.

Thanks for the tip! I'll definitely check them out.
 

Offline ROFLCat

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #53 on: October 25, 2020, 08:17:05 am »
Check out Linear Technology application notes 83 and 124 for example circuits.

^This. Application notes are gold mines of good advise and practical uses of different components and technologies. On the topic of low-noise amplifiers for instance there's this guy who built a reasonable amplifier circuit based on a couple of application notes:


AND he builds the device to characterize low-noise regulators and power supplies, so it might be well in line with OP's request.

Even more, the guy is actually using a 70Mhz Hantek DSO5072P scope (which is a model someone here already suggested) and seems to work just fine for the job.

I think brands like Hantek/Mustool/Owon/whoever-the-original-oem-of-those-devices-is are doing a pretty good job at making decent entry-level oscilloscopes that are WAY beyond the specs of what hobbyist had access to even 10 years ago. They are definitely not state of the art, but I would have killed for one of those scopes when I started. Some of them are terrible, sure, but we are starting to see some models that definitely meet the specs, have a reasonable range of features, and don't have that many UX glitches as previous "budget" scopes.

Now, sure, if you can afford a Rigol or a Siglent ( or if you happen to find a good deal for a second hand <reputable brand>) by all means go for it. Just don't overlook the few little gems that are coming from "generic" manufacturers. I've seen a lot of people doing amazing stuff with them already.

I'll check it out. Thanks :D

Yeah some of these are making a comeback.
I'm still waiting for the prices to drop down and seeing if there are going to be any good second-hand models for sale.
 

Offline ROFLCat

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #54 on: October 25, 2020, 08:18:04 am »
You can buy a pre-built signal amplifier on Aliexpress for $5 and add a battery and biscuit tin.

Oh I don't know about that. I wouldn't wanna count on a low-noise reference with fake chips.
 

Offline Fungus

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #55 on: October 25, 2020, 11:27:43 am »
You can buy a pre-built signal amplifier on Aliexpress for $5 and add a battery and biscuit tin.

Oh I don't know about that. I wouldn't wanna count on a low-noise reference with fake chips.

Not everything is "fake" on there.  :-//

The point is that no oscilloscope magically solves the problem of measuring noise.
 

Offline mawyatt

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #56 on: October 25, 2020, 01:30:29 pm »
You can buy a pre-built signal amplifier on Aliexpress for $5 and add a battery and biscuit tin.

Oh I don't know about that. I wouldn't wanna count on a low-noise reference with fake chips.

Not everything is "fake" on there.  :-//

The point is that no oscilloscope magically solves the problem of measuring noise.

Nope, Tektronix did this 50 years ago with the 7A22 Differential plug-in. Quite good actually at measuring low frequency noise, even had selectable built-in separate LP and HP filters for setting the BW as well as variable offset introduced near the front end to help with post-amplifier saturation. We had a number of these for use with our sub-nanovolt/root Hz amplifiers/systems and other ultra-low noise endeavors.

The amplifier you mentioned is worthless for the low noise low frequency reference measurements, the LT app notes mentioned by D Hess is what's required, especially in front of a really noisy low-resolution scope ;)

If you want to learn about low noise scope measurements, study the 7A22 design/notes, the mentioned LT App notes, and the video.

BTW the old Tektronix Main Frame scopes allowed various "plug-ins" for both vertical and horizontal, these were the workhorse analog scopes which could be tailored by plug-ins for covering a large range of measurements, including the mentioned low noise references.

Best,
« Last Edit: October 25, 2020, 01:32:07 pm by mawyatt »
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Offline ROFLCat

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #57 on: October 31, 2020, 10:18:38 am »
Hello again!

So today a new ad popped up, it's a Philips PM3315 125MHz, 2 channel 'scope with 3 waveform memories and good amounts of trigger options for less than $90. The tube seems bright and consistent, the chassis looks extra clean but the seller says that some volts/divs need calibration and they're a bit off and he says the main power button sometimes doesn't turn it on and it can probably be fixed with some cleaning. It doesn't have any probes though. I don't know, do you guys think I should just go for it and buy separate probes? (Most probes available are Chinese with crappy plastic :( ) I can see a 60MHz Taiwanese probe for about $20 and from the same company but 250MHz is $50, more than half the price of the scope LOL.
 

Offline battlecoder

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #58 on: October 31, 2020, 05:04:54 pm »
Hello again!

So today a new ad popped up, it's a Philips PM3315 125MHz, 2 channel 'scope with 3 waveform memories and good amounts of trigger options for less than $90. The tube seems bright and consistent, the chassis looks extra clean but the seller says that some volts/divs need calibration and they're a bit off and he says the main power button sometimes doesn't turn it on and it can probably be fixed with some cleaning. It doesn't have any probes though. I don't know, do you guys think I should just go for it and buy separate probes? (Most probes available are Chinese with crappy plastic :( ) I can see a 60MHz Taiwanese probe for about $20 and from the same company but 250MHz is $50, more than half the price of the scope LOL.
First, that's a REALLY good price in my opinion.  HOWEVER...
From my experience I can tell you that calibrating a scope normally requires pretty precise function generator and other gear. This is especially an issue when it comes to >20 Mhz scopes, because you start getting into the terrain of reasonably high-frequency signals where no cheap instrument will dare tread.
In fact, this is something I struggled A LOT with, when I had to calibrate a 100Mhz analog scope. The HF circuitry was reasonable complex and required gear I didn't have. I ended up cobbling together a high-frequency square-wave generator myself, and verifying the readings against a 100Mhz digital scope, which is definitely NOT the way the service manual recommended. At most I can say it ended up "more or less as poorly or well calibrated as the other guy"  :-//

So buying that scope might end up buying yourself a week (or more) of quality time with the scope partially disassembled over your dining table while you desperately try to come up with the signals and measurements you need to verify that it's performing as expected trhough its full bandwidth.

Regarding Chinese probes, some are pretty decent, to be fair. I have bought a couple sets for different scopes, and I'm yet to find a reason to complain about them. In fact, I'd say the last set I bought seems to work better than the probes that came with my Rigol scope (that doesn't make them good probes, but at least makes them better than what Rigol considers a good probe set for their entry-level scopes). Just make sure they are reasonably above the scope's bandwidth to avoid problems with the conversion ratio between "real Mhz" and "$20 with free shipping Mhz".  :-DD
« Last Edit: October 31, 2020, 06:13:52 pm by battlecoder »
 

Offline ROFLCat

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #59 on: October 31, 2020, 05:59:13 pm »
You're right, the calibration does need good equipment that I don't have either. The price/performance is amazing but the calibration thing... Oof.

I found a set of two 100MHz probes for $12 LOL.
 

Offline Fungus

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #60 on: October 31, 2020, 06:16:51 pm »
You're right, the calibration does need good equipment that I don't have either.

It doesn't have to be very precise for you to be able to use the 'scope. Most usage of an oscilloscope is looking at the shape of waves together with an approximate voltage measurement, eg. many DSOs are only specified to about 5% accuracy on the voltage readings.

So... if you can generate an accurate 5V square wave then
a) You can calibrate the most common scales directly from that.
b) For the mV voltage scales you can feed your 5V though a 10 turn potentiometer, adjust it to output the voltage you need by measuring with a multimeter, now feed your square wave through that to calibrate the 'scope.

I found a set of two 100MHz probes for $12 LOL.

Finding probes for a 125MHz 'scope shouldn't be a problem.
 

Offline ROFLCat

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #61 on: October 31, 2020, 06:24:28 pm »
You're right, the calibration does need good equipment that I don't have either.

It doesn't have to be very precise for you to be able to use the 'scope. Most usage of an oscilloscope is looking at the shape of waves together with an approximate voltage measurement, eg. many DSOs are only specified to about 5% accuracy on the voltage readings.

So... if you can generate an accurate 5V square wave then
a) You can calibrate the most common scales directly from that.
b) For the mV voltage scales you can feed your 5V though a 10 turn potentiometer, adjust it to output the voltage you need by measuring with a multimeter, now feed your square wave through that to calibrate the 'scope.

I found a set of two 100MHz probes for $12 LOL.

Finding probes for a 125MHz 'scope shouldn't be a problem.

Ah true. An "issue" that has come up is that the seller has made the 'scope private for an individual who may be buying. If they don't, then I can maybe buy it.

Probes are easy to find, just a bit expensive.
 

Offline Fungus

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Offline battlecoder

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #63 on: October 31, 2020, 08:00:58 pm »
It doesn't have to be very precise for you to be able to use the 'scope. Most usage of an oscilloscope is looking at the shape of waves together with an approximate voltage measurement, eg. many DSOs are only specified to about 5% accuracy on the voltage readings.

Well yes and no.
Yes; It doesn't need to be precise to be useful for watching shapes (unless you want to look into high-frequency ringing and artifacts). But from what I remember OP was interested in measuring ripple, noise, and whathaveyou. For that I think he'd need the device to be as precise as possible, so a quick basic calibration with a breadboard square gen might not be enough.

Of course buying it now, and solving the calibration aspect later is an option. I'm sure there's a lot of people here who can MacGyver a calibration procedure for a 125Mhz scope with readily-available parts and gear, and would be happy to chime in.
 

Offline Fungus

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #64 on: October 31, 2020, 08:49:32 pm »
from what I remember OP was interested in measuring ripple, noise, and whathaveyou. For that I think he'd need the device to be as precise as possible.

yes and no.

You want to be able to see it. You want to know how it changes when you do things to the circuit. Absolute accuracy? Maybe not as important as you might think. A bigger problem would be if there was a huge jump between ranges.

I'm sure something reasonably accurate can be done without spending a lot of money. The "square wave and pot" was just a starting point.

It might just be a dirty switch and the problem will go away with a can of contact cleaner.  :-//

The best thing is to find a place where people know that model and ask their opinion.
« Last Edit: October 31, 2020, 08:54:30 pm by Fungus »
 

Online nctnico

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #65 on: October 31, 2020, 08:55:56 pm »
It might just be a dirty switch and the problem will go away with a can of contact cleaner.  :-//
Please no contact cleaner! Makes things work for a week or two and then everything is fubar due to corrosion. A better approach would be to get a service manual first to see what can be adjusted and perhaps clean switches and potmeters gently with alcohol. Not sure whether that will improve things because once a switch or potmeter is worn it simply needs to be replaced in order to get a piece of equipment back to work properly.

Given the problems the OP describes I'm not sure whether the scope was a really good purchase but then again it was cheap. I would have gone for any reasonable modern DSO.
« Last Edit: October 31, 2020, 08:58:58 pm by nctnico »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline rf-loop

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #66 on: November 01, 2020, 05:15:38 am »
...and perhaps clean switches and potmeters gently with alcohol.

There are many many alcohols.

I do not recommend ethyl alcohol for this kind of work. Ethanol need keep away until very special known reason for use it in some specially named place.

Mostly, right alcohol is isopropyl alcohol (isopropanol) Aka IPA.


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Offline ROFLCat

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #67 on: November 01, 2020, 09:51:03 am »
So... Anymore ideas and reasons to buy it?
 

Offline ROFLCat

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #68 on: November 01, 2020, 10:01:29 am »
The seller just messaged me that the other person didn't buy it and they've re-posted the ad. He says he wants to sell it outside of the website and "you'd better get it soon", probably trying to trigger me LOL.

I still haven't decided because even though I probably could fix it, I don't like the chance of blowing off the money I can't restore on something that's half working.

Update: I told the guy that I'm not interested and that he shouldn't wait for me.
« Last Edit: November 01, 2020, 10:19:21 am by ROFLCat »
 

Online nctnico

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #69 on: November 01, 2020, 10:39:36 am »
The seller just messaged me that the other person didn't buy it and they've re-posted the ad. He says he wants to sell it outside of the website and "you'd better get it soon", probably trying to trigger me LOL.

I still haven't decided because even though I probably could fix it, I don't like the chance of blowing off the money I can't restore on something that's half working.

Update: I told the guy that I'm not interested and that he shouldn't wait for me.
Good choice. BTW don't worry about probes. Used probes that come with oscilloscopes are usually crap and need replacing anyway.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline Fungus

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #70 on: November 01, 2020, 11:13:29 am »
Update: I told the guy that I'm not interested and that he shouldn't wait for me.

What's the plan now? Rigol DS1052E?
 

Offline ROFLCat

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #71 on: November 01, 2020, 04:13:20 pm »
The seller just messaged me that the other person didn't buy it and they've re-posted the ad. He says he wants to sell it outside of the website and "you'd better get it soon", probably trying to trigger me LOL.

I still haven't decided because even though I probably could fix it, I don't like the chance of blowing off the money I can't restore on something that's half working.

Update: I told the guy that I'm not interested and that he shouldn't wait for me.
Good choice. BTW don't worry about probes. Used probes that come with oscilloscopes are usually crap and need replacing anyway.

Yeah that's not an issue. I can get two 100MHz probes for $12 which I think is a pretty good deal.
 

Offline ROFLCat

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #72 on: November 01, 2020, 04:16:30 pm »
Update: I told the guy that I'm not interested and that he shouldn't wait for me.

What's the plan now? Rigol DS1052E?

Yes and no. I'm still waiting for that company to give me a quote on the price to order a DS1054Z from China. I'm also waiting for other ads for 'scopes to pop up.
They do from time to time but most of them are crappy 20MHz broken ones which are also way overpriced.
« Last Edit: November 01, 2020, 04:22:48 pm by ROFLCat »
 

Offline ROFLCat

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #73 on: November 05, 2020, 10:16:17 pm »
*Sigh*
The company I was hoping to be able to import from TaoBao for cheap just told me it would be about $900 to import a DS1054Z which is just stupid frankly.

I guess I'll just wait for the economy to get better or until I find a good second-hand one.

Meanwhile, I got into a great university with amazing labs and stuff (haven't seen the EE lab but the labs for other fields are just chocked full of equipment worth tens of thousands of Dollars). The problem is that the human malware won't let me go into the building and use the equipment. Great.
 

Offline ROFLCat

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Re: I Need Help With Choosing a Budget Oscilloscope!
« Reply #74 on: November 07, 2020, 12:44:55 pm »
Wow! An ad for a Tektronix TDS 220 popped up. 100MHz, 1GS/s, and 2 channels. It's a bit of an old model but I think it's pretty sweet, listed for about $330 and I can buy it in less than a day. The seller says it's fully functional and clean. I don't know if he would include the probes or not so I just asked and I'm waiting for an answer.

Should I go for it? An alternative to this would be a DS1052E which is more expensive or a GW Instek 'scope with very low specs (like 40MHz or something).

Update: They replied and told me it has 1 probe.
« Last Edit: November 07, 2020, 01:19:34 pm by ROFLCat »
 


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