Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: Vogavt on December 31, 2011, 12:32:29 AM
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I know very little about oscopes but have used them some at a former job.
I've searched through many threads that popped up from the search feature here in the forum as to what and how one could use them, where to connect the probes to obtain various readings, etc. to compare to what is shown in Mach, i.e., what is actual versus expected.
However, I didnt' find much information regarding such; only things like "if you have an oscope you could see..." or "hook up your oscope and look for ....".
I think they are fascinatiing tools but just don't know where to start if I were to purchase one. My main reason for wanting one is to know where and how to look for possible lost steps or anything else someone would care to share with me.
Any insight would be most appreciated!
Vogavt
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Hi Vogavt,
Just one tip - If you are using a mains operated oscilloscope (without an autotransformer or other means of isolation) make sure the earth connection of the probe is only connected to an earth point on your machine. Shorting various unknown points to earth while testing can ultimately spell disaster. :'(
The portable, battery operated, hand held scopes are in may ways a lot safer to use when it comes to trouble shooting as they have a floating GND and the above does not apply. ;)
Tweakie.
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Thanks for the tip!
Has anyone put together any sort of document that spells out clearly something to the effect of "connecting probe here and here will allow you to and look for ..."? I would think that would be a very useful piece of information.
My only thoughts are not everyone is using the same BOB's, etc., which miight muddy the water. However, if there is knowledge of commonalities between board's pins then it might be a starting point.
Treat me like a newbie when it comes to this..
;D
Vogavt
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uNless you are looking for some specific problem it will be of little help and probably more confusing than help.
Just a thought. (;-) TP
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uNless you are looking for some specific problem it will be of little help and probably more confusing than help.
Just a thought. (;-) TP
agreed
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Hmmm..
Okay, so back to the original thought. I've seen several questions/comments posted here about problems and someone stated "if you have an oscope you could see..." or "hook up your oscope and look for ....".
Again, not much to go on since the replies don't typically give anything much in detail
So, per your comment, let's look at something specific: let's say I'm missing steps.
How and where would I connect the probe from the oscope to see whether it's a board issue or software?
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Hi Vogavt,
I understand your thinking but it can be much more involved than just connecting up the probes.
The O'Scope screen displays a graph with (usually) Voltage on the Y Axis and Time on the X Axis but interpretation or understanding of that graph can take a lot of experience. To many the display is very pretty but totally meaningless.
I don't wish to appear disrespectful but I suggest you start at the beginning and research o'scope techniques which could be a vast subject and certainly beyond the scope of this forum.
This may be a good place to start http://www.doctronics.co.uk/scope.htm but there are many other tutorials available.
Tweakie.
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Once you have basic understanding of how the scope works and is set up, it's limitations, then you need some experience using it along with the understanding of what and how you are measuring the circuit. Without the electronics knowledge background the instrument can quickly become nothing more than a boat anchor.
Trying to find missing steps cans really be a challenge, for instance, relative to software one would need to ask......
What am i measuring?
Is the software at fault, motherboard, port, something in between or along the way........
How do i isolate the circuit for sampling
Is my scope adequate to do the job......
So echoing what was said........... beyond the scope of this forum.
RICH
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Thanks for the responses.
Don't need another "pretty" boat anchor around.
;D
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Thanks for the responses.
Don't need another "pretty" boat anchor around.
;D
Sounds like a wise choice to me. ;)
Tweakie.
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I agree that using a scope for looking for missed steps is probably not the best way to go, but a scope can be invaluable for troubleshooting and building circuits. Look at it like a 2 axis display. The vertical axis shows voltage and horizontal axis shows time. Connect your probe ground to the DB25 ground and the probe tip to the pin yo want to measure. When Mach is sending pulses, you can very accurately see the pin voltage and timing. You can set the scale to zoom in and out. If you have a multi-channel scope, you can connect to the direction and step pins and see the relationship and timing between the two.
When looking for a scope, don't go cheap. The better the scope the easier it will be to use. Get at least 20MHZ and make sure it is a digital storage scope. Most of the decent scopes will trigger on a falling or rising edge. This is important for capturing serial input. Without the ability to edge trigger, you would never be able to see or capture the serial data coming in. The better scopes will also automatically detect probe attenuation (1X, 10X, etc.).
You can buy a good scope these days for around $500. It is an instrument that comes with a learning curve, but don't let that discourage you.