EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: Arch on February 12, 2014, 12:09:33 am
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Hi, I just picked up a cheap (emphasis on cheap!) Siglent SDS1052DL and I seem to get a lot of noise. It's not so bad when there is no probe connected (I think it works as everyone would expect) but when I connect the probe it starts to get a bit of noise which is not so bad, but when I turn on the fluorescent light above my bench it can have up to 100mv pp of noise that seems to be forming a sine wave within a sine wave
Now, there are a bunch of things with this oscilloscope that has disappointed me so far (for example when it freezes for a split second when it triggers, or when the built in square wave works perfect but I adjust the vertical resolution, a relay clicks, and the bottom of the square wave becomes a steep slope all of a sudden) so I think I am returning it and I will save for a better oscilloscope at a later date.
So, questions for my future decisions:
- I have a wireless router that is probably under a metre away, should this cause noise? I imagine the probe can act as an antenna? Or should this not happen if the probe was decent?
- Is it normal for a fluorescent light to cause so much noise? the light is maybe 2/3 of a metre above my desk
- Is it normal for a scope to freeze for a split second when triggering?
- I was looking in to the rigol DS1074Z as a scope to buy at a later date, is this considered decent for a hobbyist? Or does it still have annoying problems like the cheaper scopes? Does it freeze when triggering?
- As usual, the device says keep out of direct sunlight; does this include light passing through windows? (I guess this is a little unrelated but I am curious)
- Does it matter where the power cable is plugged in? Does it have to go direct to the wall, is a surge protector ok if it's grounded, what about with a UPS?
My current reason for getting the scope is because I am trying to get in to building some guitar pedals for myself and I would like to know what is actually happening. I think I measured my guitar giving off over 400mv ac sometimes if I strum it so the 100mv noise makes using this scope ineffective for me
I think my goals are changing to get a proper work bench and move away from the router first, and then a decent scope like the rigol above if it's good enough for guitar signal analysis
I am mostly interested in the compact form/nice screen of the digital storage scopes and I find 7" screens are like a sweet spot for any smaller device but would there be a reason I should prefer an older used analog scope for my purposes? Would an analog scope be better for viewing guitar signals? I was going to buy one, but I found the siglent for the same price and it's more convenient for my current workspace. Maybe it was a bit of a mistake to buy in to it's looks and form :P
I am part way through the scopes for dopes video and it looks like it'll be a good watch, and I think I watched all the eevblog multimeter videos a couple of times each and decided I would upgrade from my $20 cheapie to a fluke 87V. At least I am happy with that purchase :P
Is anyone else from toronto and thinks that it's oddly annoying trying to get test and measurement equipment here? Everything is so much more expensive to buy or it's difficult to find a product that doesn't cost $100 to ship + whatever brokerage fee the shipping companies charge for importing in to canada
Anyway, enough from me for now :blah:
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Regarding the noise - an unconnected probe can easily pickup noise like that from the lighting ballasts, etc., as well as from the mains wiring. The real questions are - does the noise exist if you short the probe tip to it's ground connection? - does the noise exist if you connect the probe's ground to your circuit's ground? If the answer to either of these is yes, then it sounds like you have a fault somewhere.
Regarding "freezing" when triggered - what you're likely seeing is what happens when the scope switches from "Auto" trigger to normal trigger. The "auto" trigger circuit looks to see if there is a valid signal to trigger on, and if it doesn't see one in a little while, it sends its own trigger anyway. It continues to do this until it gets a "real" trigger. Some scopes take a while to switch between these modes, some do it nearly instantaneously. Check out my videos on triggering controls, and the one on auto-triggering, for more information.
For your case, where you are looking at complex audio waveforms and not triggering on anything in particular, you can use the trick where you tell the scope to trigger on the "Line", which will cause the scope to trigger on the line voltage frequency continuously, so there won't be any switching between auto and normal, and the scope won't freeze on you.
An analog scope is nice for it's instant response on varying analog signals, etc., but won't help you too much if you need to examine waveforms in detail for distortion, clipping, etc. Personally, I use an analog scope for most of what I do on my hobby bench.
I hope this info helps...
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I'm not sure what your knowledge level is but check some the following.
- Calibrate the scope, it's in the manual (warm up time 30 minutes before doing a cal)
- Generally your probes should be set to and compensated for x10, you must also set the scope to the same. It's in the manual.
- Yes cheap scope. I'd say play with it and see what you can make it do.
Have fun.
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Regarding the noise - an unconnected probe can easily pickup noise like that from the lighting ballasts, etc., as well as from the mains wiring. The real questions are - does the noise exist if you short the probe tip to it's ground connection? - does the noise exist if you connect the probe's ground to your circuit's ground? If the answer to either of these is yes, then it sounds like you have a fault somewhere.
Regarding "freezing" when triggered - what you're likely seeing is what happens when the scope switches from "Auto" trigger to normal trigger. The "auto" trigger circuit looks to see if there is a valid signal to trigger on, and if it doesn't see one in a little while, it sends its own trigger anyway. It continues to do this until it gets a "real" trigger. Some scopes take a while to switch between these modes, some do it nearly instantaneously. Check out my videos on triggering controls, and the one on auto-triggering, for more information.
For your case, where you are looking at complex audio waveforms and not triggering on anything in particular, you can use the trick where you tell the scope to trigger on the "Line", which will cause the scope to trigger on the line voltage frequency continuously, so there won't be any switching between auto and normal, and the scope won't freeze on you.
An analog scope is nice for it's instant response on varying analog signals, etc., but won't help you too much if you need to examine waveforms in detail for distortion, clipping, etc. Personally, I use an analog scope for most of what I do on my hobby bench.
I hope this info helps...
There is definitely still noise when I am connected to circuits. I tried connecting to a circuit I threw together the other day, and to one that was built in the 70's in a factory. Both run on a 9v battery if that matters.
I'll take a look at your videos, I am not sure what triggering on the "Line" is exactly from that definition but I'll watch the videos and come to some conclusions and if not I will come back to ask more questions :D
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I'm not sure what your knowledge level is but check some the following.
- Calibrate the scope, it's in the manual (warm up time 30 minutes before doing a cal)
- Generally your probes should be set to and compensated for x10, you must also set the scope to the same. It's in the manual.
- Yes cheap scope. I'd say play with it and see what you can make it do.
Have fun.
I haven't tried waiting 30 mins to do a self calibration but maybe I will try
I set the probes to x10 and set it in the scope too and it doesn't seem to resolve any issues
Definitely playing with it, even while having problems I feel that I am learning :P but maybe that is the best way to learn
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First you can take this as playing around but it does have some real use.
- Try hooking both probes up to the same source, you should of course see the same signal.
- The autoset will have a few triggering options. Push menu on (if it isn't already) then hit autoset. The autoset options should appear. You will have the same options under single shot but need to set the trigger level.
- Hit CH1 or CH2 and select filter type. These are software filters and really fun for audio work. Not ideal to leave on permanently because of course they remove part of your signal. Too much 60hz just dial it out.
- fft is really fun, hit math then push the top menu button until you see FFT.
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How long is the ground lead on your probe?
Is the noise there when you short the probe tip to the ground lead?
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First you can take this as playing around but it does have some real use.
- Try hooking both probes up to the same source, you should of course see the same signal.
- The autoset will have a few triggering options. Push menu on (if it isn't already) then hit autoset. The autoset options should appear. You will have the same options under single shot but need to set the trigger level.
- Hit CH1 or CH2 and select filter type. These are software filters and really fun for audio work. Not ideal to leave on permanently because of course they remove part of your signal. Too much 60hz just dial it out.
- fft is really fun, hit math then push the top menu button until you see FFT.
I tried these out quickly, pretty neat :P Not sure what I was seeing with the FFT stuff, it was bouncing around like crazy lot when I was on the square wave test signal. I'll have to read up on the filter options, there were icons I am not familiar with...maybe it's in the manual
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How long is the ground lead on your probe?
Is the noise there when you short the probe tip to the ground lead?
The ground lead is just over 6"
When I connect the ground lead to the tip of the probe, the scope shows a relatively nice line
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If you have a memory stuck you can plug it in the front usb connector and hit the print key. That will put a picture of the screen on the stick and you can post it if you like.
- Filters are equivalent to tone and treble setting on an amp but they are much more selective. You could set them for example to listen to everything above, below equal to or not equal to the note "G". Very handy for audio work.
- FFT (Fast Fourier Transformation) Shows what we call the "frequency domain". It's probably easier if I just say that it can show you individual notes from your electric guitar.
- That scope also has a hardware frequency counter, also a very handy tool for audio work.