Oscilloscope range improvement - Page 1
Forum section: electronics / beginners

author: turbolargo
author_rank: Newbie
timestamp: March 02, 2016, 01:49:10 pm
content: Hello, my name is Daniel and i just bought a 20€ ebay DIY oscilloscope kit (DSO138)I got it working and performs just fine, the issue is that the multiplier options are x5 x2 and x1, the volts per division options are 1V 0.1V and 10mV and the display has about 10 divisions.I can't figure out how to make a 25V sine wave fit in the super small display this has, I have most of the sine wave going over the upper and lower display limits.Is there any way I can modify either the oscilloscope or the signal to make 230V fit?

author: Simon
author_rank: Unknown
timestamp: March 02, 2016, 02:04:43 pm
content: If you are looking at the mains be very careful and make sure your scope is not grounded but battery powered. You will need at the very least a potential divider (2 resistors) but really it is a bad idea to put such a low level peice of kit on the mains, it probably has no protection. The way I look at mains it with 2 channels and I use the scopes math function to take the difference between them.If you are just curious use a transformer.

author: exe
author_rank: Unknown
timestamp: March 02, 2016, 02:06:50 pm
content: > 25V sine wave fit in the super small display thisMay be resistor voltage divider?Just be sure you are not overloading the scheme with the divider.> make 230V fit?Huh, this can be dangerous... Why do you need this? Anyway, first please check this video:(EEVblog #279 - How NOT To Blow Up Your Oscilloscope!).

author: tggzzz
author_rank: Super Contributor
timestamp: March 02, 2016, 03:59:46 pm
content: Quote from: turbolargo on March 02, 2016, 01:49:10 pmYes, but only if you know exactly what you are doing. Get it wrong and there can be loud noises followed by deathly quiet.If you are only curious about looking at the mains, use an isolated mains to low voltage transformer.If you reallyneedto look at the mains with a scope and there is no alternative, see the safety references inhttps://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/

author: TinkerFan
author_rank: Regular Contributor
timestamp: March 03, 2016, 09:50:11 am
content: You should also remember, that the 230V are rms, so the real amplitude will be more about 320V, but that shouldn't matter too much when you've 10 divisions and a x100 probe/divider

author: tautech
author_rank: Super Contributor
timestamp: March 03, 2016, 10:26:28 am
content: Quote from: turbolargo on March 02, 2016, 01:49:10 pmDon't.Why on earth would you want to?Do understand that use of this DSO on anything other than low voltage WILL put yourself at risk.Using appropriate equipment (not yours) and to be at low risk one would use either a HV Differential probe or a 100:1 probe.Stay safe.

author: turbolargo
author_rank: Newbie
timestamp: March 03, 2016, 11:29:48 am
content: Quote from: TinkerFan on March 03, 2016, 09:50:11 amI didn't take that into account, also it's 8 divisions, just realized i bought crap, I made a mistake there :/

author: turbolargo
author_rank: Newbie
timestamp: March 03, 2016, 11:34:44 am
content: First thanks to everybody,It is battery powered, so I'm pretty sure I'm not going to short anything.I wanted to use it to take a look at AC motor controller that is not working properly, I believe it's controlling the speed with a dimmer like circuit so that's why I needed an oscilloscope.Now that you know the real case, will a transformer do the job or should I better go for a voltage divider?

author: turbolargo
author_rank: Newbie
timestamp: March 03, 2016, 11:40:50 am
content: Quote from: tggzzz on March 02, 2016, 03:59:46 pm

author: tggzzz
author_rank: Super Contributor
timestamp: March 03, 2016, 11:41:55 am
content: Quote from: turbolargo on March 03, 2016, 11:29:48 amIt may or may not be crap.It isn't suited to displaying mains voltagesdirectly. But thenyou probably shouldn't be doing that withanyscope.You haven't said why youneedto be able to display mains voltage directly; whatresultdo you want toachieve?Engineering is about working out what you need to achieve, and then using imagination knowledge and skill to find a way of doing it with whatever is available.

author: turbolargo
author_rank: Newbie
timestamp: March 03, 2016, 11:48:45 am
content: Quote from: tggzzz on March 03, 2016, 11:41:55 amThere are two main reasons, as I just explained I have an AC motor controller not working properly and I believe it's controlling the speed with a dimmer like circuit.Also I wanted to take a look at a UPS (backup mains battery) output to see how nice it is performing.

author: Lost resistor
author_rank: Contributor
timestamp: January 25, 2025, 08:05:15 pm
content: Op was asking about improving voltage range, im wondering if i can increase sample rate?On official website there is a quick guide on library used to make this thing an "oscilloscope":https://jyetech.com/wp-content/uploads/2018/07/dso138-library-how-to.pdfIm just not sure how would i go about improving time base range (getting smaller time base)? is it already maxed out, or can i increase it? Im simply interested in viewing proper shape of "higher frequencies", ai. 150-200kHz signals.If it makes sense would it help reducing horizontal capture? and using time used to capture things outside of screen to process limited amount of stuff that would only fit on screen? Somewhat like analog oscilloscope, without any buffer, just what is displayed on screen.What i also want to achieve is using this, and open source nature of it, to learn more about microcontrollers, oscilloscopes, ect. and how would i go abut making my own oscilloscope. (for fun and demo purpose)

author: tautech
author_rank: Super Contributor
timestamp: January 25, 2025, 08:58:34 pm
content: Quote from: Lost resistor on January 25, 2025, 08:05:15 pm50+ years ago it was obvious that to do measurements one can trust as accurate, the right gear is needed.Make the investment in such and get on with enjoying your hobby rather than disappearing into another rabbit hole.... been there done that !BTW, one should know every measurement taken actually affects the measurement value.Study up on 'measurement circuit loading' and you'll find some good papers online.

author: Lost resistor
author_rank: Contributor
timestamp: January 25, 2025, 09:40:06 pm
content: I know i knowbut they arent exactly cheap in my country, at least 2/3 of minimum wage. Maybe if i considered usb ones?I know about circuit loading, but as i said, i thought it would be interesting project to try to change this, as well as making "oscilloscopes" from other IDE-s, such as arduino and so on. Not for purpose of making a functional oscilloscope, but playing with embedded electronics, ADCs, ect.I did some really basic stuff in college, but now i would like to expand on that and try some actually practical stuff.

author: Oilngas
author_rank: Contributor
timestamp: January 26, 2025, 02:34:47 am
content: The instruction sheet for the DSO138 states: "Allowed maximum signal input voltage is 50Vpk (100Vpp) with the clip probe"

author: Analog Kid
author_rank: Super Contributor
timestamp: January 26, 2025, 04:35:27 am
content: Sheesh; it's a battery-operated 'scope, for chrissakes. So no problems with snagging a hot ground.Assuming the OP is well aware of the dangers of working around high-ish voltages (230-240 VAC is high in my book), then all they need is a good voltage divider to be able to look at at 230-240 VAC signal. Use high-value resistors, suitably soldered to something to avoid contact.OP: you do know how to avoid electrocuting yourself, yes? Please tell us that you do.

author: newbrain
author_rank: Super Contributor
timestamp: January 27, 2025, 03:33:04 pm
content: Quote from: Analog Kid on January 26, 2025, 04:35:27 amMaybe they are, maybe they weren't and that's why we heard last from them in 2016...

author: BennoG
author_rank: Frequent Contributor
timestamp: January 27, 2025, 08:32:09 pm
content: Quote from: turbolargo on March 03, 2016, 11:48:45 amThis is probably an inverter and not a dimmer.Inverters work on a different principle then a dimmer (verry different)Benno