Extremely basic oscilliscope questions for a beginner - Page 1
Forum section: electronics / beginners

author: sofakng
author_rank: Regular Contributor
timestamp: September 06, 2018, 07:43:05 pm
content: I'm trying to learn electronics and I purchased a Rigol 1054Z during an eBay sale at the beginning of the summer but I haven't learned too much yet.I'd like to troubleshoot an HDMI connection and the HPD signal (0-5v on/off) and the +5V power quality.My theory is that the HPD line is dropping below 5v causing drop-outs on my TV and I'd like to if this happening and if so, how often it's happening. I'd also like to see the +5V signal (different wire) and how closely it's sticking to 5.0v.Here are my questions:1) Does a digital oscilloscope draw from left to right and then once it reaches the right, it continues drawing from the left again? I think of a signal as continuous; starting and then going on forever so this type of display is confusing me...2) Do I want to use ROLL MODE for my above measurements? I'm not looking at a wave form in my situation, but instead want to see how often an event is occurring and the quality of a signal. Also, does roll mode function more like I describe above (ie. a signal going on forever constantly drawing on the right side of the screen... this seems more useful than a left-to-right, left-to-right, type of display?)Sorry for my extremely basic questions! I'm trying to read, watch, and learn as much as possible but some things I just can't get through my thick head.

author: ArthurDent
author_rank: Super Contributor
timestamp: September 06, 2018, 08:00:48 pm
content: Generally the ‘roll’ mode is for very slow signals. If you’ve seen medical monitors where they are displaying heart rate, the current image position appears centered as the trace is scrolling across the screen from right to left.The older scopes that had CRTs would sweep from left to right across the screen then there was a ‘blanking pulse’ that would allow the trace to almost instantly zip back to the left where it would start drawing again. The new scopes do something that looks the same but they are displaying what is written in memory on the LCD screen.

author: vk6zgo
author_rank: Super Contributor
timestamp: September 07, 2018, 12:59:43 pm
content: Analog 'scopes have a function which was commonly referred to as "free running", where the sweep is running continuously, not needing triggering from any input signal.This was convenient for looking at DC voltages, as when DC coupled, the position of the line on the screen would be deflected vertically by an amount depending on the voltage & the volts/div setting of the Oscilloscope.With early DSOs, there was not a real equivalent function, meaning that people had to use "work arounds".The "roll" mode was one of those used, but it was not very useful, seeing & displaying the change in voltage as a slow pulse.Modern DSOs do have a real equivalent to "free run" & can be used in the same way as their analog predecessors.

author: StillTrying
author_rank: Super Contributor
timestamp: September 07, 2018, 02:08:03 pm
content: Quote from: vk6zgo on September 07, 2018, 12:59:43 pmJust AUTO trigger on a DSO ?When probing mostly DC voltages such as around a logic IC, AUTO trigger keeps starting and stopping, ....so I sometimes switch the trigger to AC line, which gives a permanent trace, which you see flicking up to 5V - or not, without taking your eyes off the IC pins/probe.

author: vk6zgo
author_rank: Super Contributor
timestamp: September 07, 2018, 04:47:33 pm
content: Quote from: StillTrying on September 07, 2018, 02:08:03 pmWould it be better with a faster time /div setting in AUTO? (that's also what they call it on analog 'scopes)I didn't bring up the term AUTO because of possible confusion with the AUTOSET button on DSOs.I think there was a discussion on this forum about AUTO trigger.From memory, the repetition rate of drawing the line on a DSO in that mode doesn't directly follow the time/div setting, (It is quite a bit slower, whereas with an analog instrument it is a little bit faster), but it does change with the setting of that control.I don't have a modern (or indeed, any) DSO, so any information on their function had been gleaned from the Internet, (mainly from this forum.

author: David Hess
author_rank: Super Contributor
timestamp: September 07, 2018, 05:33:21 pm
content: Quote from: vk6zgo on September 07, 2018, 04:47:33 pmThese are two different things.Automatic versus single sweep or normal just means that the sweep is triggered automatically after a timeout if no trigger event is detected. This is what creates the pause in updating the display.Automatic also may refer to how the trigger level is updated. In the event of loss of triggering, automatic level sets the trigger level to 50% of the peak-to-peak value. Unfortunately this interacts with the automatic triggering above to continuously interrupt the sweeps. Automatic peak-to-peak level is something else entirely where the trigger level is updated continuously without interrupting the sweeps and is much faster but offhand I do not know of any modern DSOs which support this.Usually the two separate configurations above are combined but they are separate on some oscilloscopes or at least on some older oscilloscopes. You might for instance want automatic sweeps without automatic level for a continuous sweep without annoying pauses.As far a the original question, I would probably start off using automatic mode with the trigger configured to continuous sweep if possible at a low time/div, say 1ms/div, and with persistence set to a longer duration just to get an idea about what is going on.Then the sweep can be set to normal and the trigger adjusted to view a specific event if there is one.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: September 07, 2018, 06:41:06 pm
content: Quote from: sofakng on September 06, 2018, 07:43:05 pmUtility > Pass/Failexplore the options underneath this menu itemuse them and your "normal" state signals to set up a Maskthe scope will identify and count instances of failure to match the Mask

author: vk6zgo
author_rank: Super Contributor
timestamp: September 08, 2018, 03:47:14 am
content: Quote from: David Hess on September 07, 2018, 05:33:21 pmIndeed!I meant with the 'scope in AUTO trigger mode, but configured to "free run".(continuous sweep)Sorry to be vague, but with an analog instrument, these functions are pretty much intuitive.QuoteMy comments about the repetition rate of drawing the line was in connection with continuous sweep.

author: David Hess
author_rank: Super Contributor
timestamp: September 08, 2018, 06:08:57 am
content: Quote from: vk6zgo on September 08, 2018, 03:47:14 amMy point is that the trigger settings can interfere with producing a continuous sweep even if no trigger is present.On oscilloscopes where this is a problem, what I sometimes end up doing is setting the trigger source to an unused channel or the external trigger so it does not interfere with the automatic sweep.