Oscilloscope help

I have set up a 555 monostable circuit and I want to watch it operate on my oscilloscope. I am pretty much a complete newbie when it comes to o-scope operation.

I have set up a circuit just like in this video and you can see where he monitors it on his scope: https://youtu.be/057q6v7uwwU?t=13m14s

I have tried and tried to replicate that, but no luck. I am hoping that I can get some help in general terms first (not necessarily button-by-button), but if that is unavoidable, I have a Rigol DS 1054.

I think it has to do with triggers. I have used triggers before, but in this case the trigger signal is a LOW. I am not sure if I am setting that up right.

Or is he not using triggers and instead just leaving the scope in "Run"?

He is probably using, ext trigger source, where he is adjusting a trigger voltage off screen.


Look at the video again. The trigger is “auto”, meaning the trigger is any change in signal. And his trigger is +, not low, as seen in the top trace on the scope. Perhaps your probe is not looking at the correct pin on the circuit.

I hope that is all correct.

Apparently I had it on the wrong pins. It worked beautifully. Very cool!

MrGibbage: Apparently I had it on the wrong pins. It worked beautifully. Very cool!

Great! Glad you figured it out.


Wrong pins can do that ;)


Last question about o-scopes for now. Why does it take so long to see the trace? When I press the button, it takes like ten seconds to see it on the scope, and then the trace slowly goes to the right, but I presume it is in real time because when the LED goes off, it happens at the same time on the scope. So why does it take so long to see it the first time? I’d love to just be able to put the probe on and see what is going on without the ten second wait.

What is your horizontal seep rate set to?

This is because your horizontal time base is so slow it takes 10 seconds to gather all the data. Wind up the time base.

DSS’s have two display modes, one is commonly used, collect the data for the whole screen, then apply
filtering etc and display it.

For slow timebase the screen will be updated in real time, often less processing is done (for a cheap 'scope at
least). The reason is that signal processing is all in the digital domain, typically using FIR digital filters which
have large sample delays which would be obtrusive when sampling at very low rates.

Oh yeah, including the timebase would have been smarter. I had it set to 5 sec/div. I needed it that slow because I had my time delay in my circuit at about 30 seconds.

I have noticed that this doesn't seem to happen at faster speeds. My guess is, it is still happening, it's just that it is fast enough that I don't really notice.

But I still wonder why it is necessary. It seems like if it is doing something that is usually desirable (i.e., a "feature"), that it could be turned off when having a long time base.

@MarkT, I think you are answering the "why", but I gotta say I didn't understand your answer. :(

I guess in the big scheme of things, I probably don't need to know why it happens, but just understand that it does and learn to work with it. No big deal, I guess.

There are quite a few instructional videos about using a DSS on YouTube.

I suggest you review these as they go through the basic usage concepts.