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Forum Index : Electronics : Don’t have a scope: need 1 or 2 on budget
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LadyN Guru  Joined: 26/01/2019 Location: United StatesPosts: 408 |
It's apparent to me that I need an oscilloscope to help me go forward with building boost, buck convertors and inverters. 1. I want to begin with most off the shelf boost, buck convertors like we can get from BangGood, eBay or Ali, which seem to uperate around 20 - 50Khz switching freq? 2. For inverter, I dont think I will be going above 10Khz myself as I want to start off with Tony's stepped sinewave idea that does not require as high of a switching freq as most SPWM inverters. The downside of that is I need to find multiple transformers but I am hoping I will learn enough to get past that point The voltage amplitudes will be + and - 300V but perhaps getting a few 10x or even 100x probes should let me scale the voltage down to what a budget oscilloscope can support? Considering this, I believe, getting a 10 * 50Khz = 500Khz oscilloscope should be good enough. Maybe 1MHz. 3 questions: 1. What are some budget oscilloscopes that fit this criteria? I saw some recommendations for $20ish small TFT screen oscilloscopes but I think they are a bit too small to use during circuit development. I just wish they had a storage feature and the ability to send to a computer or something. Is there something like that out there? 2. Are the 10x or even 100x probes a good solution to scaling down the + and - 300V inverter outputs down to what these oscilloscopes can handle, and 3. Are BangGood, eBay or Ali good sources for these 10x or even 100x probes? It's OK if I have a more capable oscilloscope (less than $100) as the main one and the ~$20 small TFT screen oscilloscope as a secondary if having this twin setup helps me achieve circuit development on a budget. If I can get started with the ~$20 small TFT screen oscilloscope and wait a few more months for a more capable oscilloscope, if the sub $100 ones are not very useful, I can do that too, but only if this approach is possible. |
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mackoffgrid Guru Joined: 13/03/2017 Location: AustraliaPosts: 460 |
Gday N The DSO138 is the cheap $20 kit getting about on Ebay. I've not used it, but I see the guys on stm32duino forum have done some alternative software for it. Those scopes will not be good enough to look at the switching of FET's that you'll be wanting to do. You'd be better of saving your money for a real DSO. This is the minimum I'd be looking at. If you look at Poida's topics you'll see snapshots of the 4ch RIGOL - I'll be talking myself into that one some time :-) RE: those DSO138: influenced by tinker's photo's, I'm building a $10 scope purely as bling for my inverter to permanently show the 50hz output. More on that later. Cheers Andrew |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Those DSO's have a sampling rate of only a few Khz, ideal for looking at 50Hz sine waves but not much else. Agree with Andrew, get a proper digital oscilloscope, whatever you can afford, it will serve you very well for a great number of years. Cheers, Tony. |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
DSO138 Found to be useful for initial troubleshooting. Agreed you want something better for design work in the 50kHz to 1MHz region. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
I am surprised that it has 1Msps, it does not seem to respond that well to fast events. One particularly good feature about it is that it stores all the user settings in non volatile memory. It can take some time to scroll through all the menu driven features so that you can finally get the display you want up on the screen. If its powered down, then powered back up again it all comes back, so its ideal for the permanent monitoring of the output of an inverter. Cheers, Tony. |
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| LadyN Guru Joined: 26/01/2019 Location: United StatesPosts: 408 |
Does it have a way to export the readings to a CSV file to a SD Card or a USB drive or even connect to a computer to download? |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Nothing like that I am afraid. Its just a very basic stand alone instrument with no outputs. You view on a very small display, whatever is connected to the input and that is it. The next step up from that would be one of the many virtual USB oscilloscopes that use a PC for display. The electrical performance would probably not be that much better, except you get a larger display, often a second input channel, and can store images as files. I still believe a real oscilloscope would be a much better buy in the long run. Cheers, Tony. |
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| joebog1 Senior Member  Joined: 07/11/2015 Location: AustraliaPosts: 114 |
I have been reading these new threads with great interest!! I have a whole bunch of CRO's that I paid $120 each for: Philips/Fluke PM3055 Ex military 60 Mhz with separate time bases. I often look at American disposal store offerings, and am green with envy at whats available. So just my two bobs worth, isnt it worth looking at whats available from disposal stores? Joe |
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| mackoffgrid Guru Joined: 13/03/2017 Location: AustraliaPosts: 460 |
Joe, Absolutely. |
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| LadyN Guru Joined: 26/01/2019 Location: United StatesPosts: 408 |
Joe, thank you for taking your time and sharing your knowledge. If I have not considered something, that means I DON'T know about it.  Do you have some links I can look at. I'm in San Diego if it helps but any link is going to be OK to get me an idea. |
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| mackoffgrid Guru Joined: 13/03/2017 Location: AustraliaPosts: 460 |
I bought my Owon PDS5022S about 15 years ago and it has served me well. Its been fast enough for everything I wanted to look at. However the memory is only 6000 samples I think. If I needed to replace it today then I would definitely spend the extra and get a 4 ch RIGOL DS1054Z (or similar). It may be twice the price of the PDS5022 but its twice the channels, 10 times faster sampling, 1 Gs/s, and the killer for me - Memory depth: 12Meg points compared to 6000 !!!! Storage depth is almost the most important spec for me. A scope is a long term asset, most of us keep them for 20+ years. The cost of a good scope is peanuts compared to the old days, and $600 over 10 + years is little more than pizza money :-) CRO's like these don't go out of date like a smart phone, or laptop computer. Believe me when I say unless you're unlucky, if you get something like the quality of the Rigol, you'll own it for many years to come. Cheers Andrew |
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Timbergetter Regular Member  Joined: 08/10/2018 Location: AustraliaPosts: 55 |
Check out the irrepressible Dave’s take on the Rigol at: https://www.youtube.com/watch?v=W2qdtQkBKhc |
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| joebog1 Senior Member Joined: 07/11/2015 Location: AustraliaPosts: 114 |
my first search brought up this https://www.bmisurplus.com/products/category/oscilloscopes all types, all prices a quick search brought up this. https://www.bmisurplus.com/products/40956-tektronix-2235-100mhz-oscilloscope That is probably more than you need =, but its hard to have "too much oscilloscope. When you go to these sites make sure the unit has been tested and is working. Exact calibration is also nice to have but not really necessary A decent meter is also required, and between the two you will soon work out any errors the unit may have. You will need probes with it, I suggest a X1 and X10 switchable unit. Thse can be bought on ebay for $25 new. Joe |
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| joebog1 Senior Member Joined: 07/11/2015 Location: AustraliaPosts: 114 |
Another seller ( this time eblech) BUT he guarantees tested and working. Its a tedious site, but his oscilloscope offerings look very tempting. I have absolutely no association with him/her/it, but after suggesting going 2nd hand I thought the least I could do is have a quick look for you. I dont know where you live, and I dont know how much shipping or postage will cost. If US postage is anything like australiapost, the cost can be as much as the unit itself!!! https://www.ebay.com.au/itm/TEKTRONIX-2445-150MHz-4-CHANNEL-ANALOG-OSCILLOSCOPE-3-94-SCREEN-TESTED/332539046422?hash=ite m4d6cdf2a16:g:LakAAOSwU91acf6q Joe |
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| LadyN Guru Joined: 26/01/2019 Location: United StatesPosts: 408 |
I am in San Diego, CA, United States. These links were very helpful! |
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yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
https://espotek.com/labrador/ usb test bench for $30. handy for tinkering, interface is good to use. I have paid a lot more for stuff I have chucked in the bin. I'm confused, no wait... maybe I'm not... |
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| LadyN Guru Joined: 26/01/2019 Location: United StatesPosts: 408 |
THAT is a really good board and the developer is super responsive unlike the DSO138 company that stopped contributing to it at all |
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9308 |
Very interesting thread, as I also am in desperate need of a decent scope. I still have my amber-screen 2GHz spectrum analyser, and it sure is useful, but it is big, heavy, and not really that portable. And to be accurate, it really needs to be left on 24/7 for temperature stability of the readings, and frequent calibration is needed, so it uses a bit of power if left on like that 24/7. I don't do that, and only fire it up a few hours before I want to make some tests on something. I hear the most consistently favourable reports about the RIGOL's, so that is probably where I would start looking first rather then the super-cheap kits or USB things. Watching this thread with interest. Smoke makes things work. When the smoke gets out, it stops! |
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| joebog1 Senior Member Joined: 07/11/2015 Location: AustraliaPosts: 114 |
Methinks, Grogster that a lil plastic box that plugs into your window will block the light!!! A REAL oscilloscope uses a big valve for da pitcher!! It doesnt need amps of current to deflect, but MAY use 25,000 thousand volts to light up the screen. It is INFINATLY fast!!! its the crappy sand amplifiers in front of it that limit the rate of change. As things "valve driven" ( or steam powered as the modern expression goes) are on the decline ( JUST like LP records), a very fine electrostatic deflection system can be bought for very small bucks. I mostly work on valves stuff so plugging 1000 volts plate voltage into my USB port sort of grates on the nerves a little. DONT overlook the wonderful old Tektronix, HP or BK types!! AND, as I remember electrons are linear and analogue ( unless the battery has a intermittent ) So it stands to reason that an analogue scope is required. I can buy three analogue electrostatic scopes for the price of your USB thingy with its 800 TINY micro-switches that fail. And what does 500 gigablob per nicekty scratch mean anyway ? My best regards Joe |
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| joebog1 Senior Member Joined: 07/11/2015 Location: AustraliaPosts: 114 |
https://www.ebay.com/bhp/analog-oscilloscope |
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