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Understanding Electronics Basics #1

Discussion in 'General Electronics Chat' started by cowboybob, Feb 16, 2012.

  1. Muttley600

    Muttley600 New Member

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    Think I've covered that now apart from questions about cicuit, but I'll let you correct me first [​IMG]

    but they have the same 'e' numbers if I'm correct even though they are two different things

    I'm doubting that now?

    I was right to doubt :-( I have checked frequency & it is wrong
     
    Last edited: Mar 22, 2012
  2. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    My Emphasis.

    KISS is correct. He's also correct that a scope can lull one into confusing the two.

    As we have been discussing the wavelength of a single cycle, it is very easy to mix both the "time" taken for the cycle to complete from start to finish (its frequency) and the "distance" traveled on the scope screen ( the number of graticules from start to finish) which is divided into time segments, from which we derive frequency. Go to the bottom of the post for a further explanation.

    But, still and all, he's right.

    No. I wanted you to see a "practical" application of the use of an RC circuit. In this case, to control the "width" (duration, or time on [or off], for that matter) of a single pulse that is controlled by the RC circuit (≈1 second). From that understanding we can investigate (and already have, actually) how an RC circuit can control the "frequency".

    It's only in this circuit that the frequency of the signal is controlled by the "period" of the trigger switch (4 seconds), which is 1 divided by 4, or 1/4 Hz, or 0.25Hz.

    Let me rephrase your sentence: "...the trigger is every 4s (true, BUT) & the pulse is every 4s also. See below:

    View attachment 62504 Please excuse the crude lettering.

    The resolution of the scope screen and a little trigger "jitter" ( an electronic excuse) is causing the less than perfect presentation. While I was looking at mine it jittered as well. When I took the snip shot it just happened to look gooder. Don't worry about it.

    No. And I'm going to have to eat a little crow here. Let's call it "wavelength in seconds" because, in point of fact, wavelength, as a term by itself, is a distance traveled, NOT a time. But for the time being, when you see the term "wavelength" think "wavelength in seconds", especially when we're using the scope.

    The time between one trigger pulse and the next is 4s, as determined by the switch. See below:

    View attachment 62505 I have GOT to get some kind of lettering app for the snip tool...

    I know this is tough, if for no other reasons trying to nail downall the definitions of all the terms. You'll eventually absorb it, so long as this instructor can quit making mistakes...
     
    Last edited: Mar 22, 2012
  3. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    I did ask you to read up until "standing waves" here: http://en.wikipedia.org/wiki/Wavelength

    λ = v/f. We haven't covered this at all. v is the speed in which it travels in the medium. In a vacuum, the speed of light is aprox 3.8E8 m/s.
    λ is the wavelength. f is the frequency and v is the velocity. This number dictates how big antenna's have to be for radio frequencies. The antenna can be any evenly divisible multiple of the wavelength long. It's not uncommon to design antenna's for 1/2 or 1/4 wavelength. Telephone antenna's are really small and a TV antenna is much larger.


    The other term you need to be familiar with is f = 1/period.
     
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  4. dave

    Dave New Member

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  5. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Teach Muttley the correct term: A wave whose period is: 395.57ms; If you want frequency do the math 1/395.57 ms.

    Making sure any answer has the correct unit has to be drilled into his head. That concept was drilled into mine a little late.

    Units are extremely important.

    PS: CBB: You haven't taught him to use the cursors, or have you?
     
    Last edited: Mar 22, 2012
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  6. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    And I know that, but I painted myself into a corner and didn't know when to stop. Thanks fro keeping an eye out for me.

    I need to amend a graphic in post# 462.

    Where I labeled the scope display "frequency", that was the wrong term.

    It should have looked and read like below:

    View attachment 62511

    Sorry for the error.

    No. I haven't. The scope face where the cursor info is displayed is extremely "busy" when data is displayed and can be quite confusing for a new user. And we haven't gotten it clear, exactly yet, as to what represents a complete cycle, so...

    But, perhaps, now is the time.

    Thanks for the input.

    CBB
     
    Last edited: Mar 22, 2012
  7. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    www.irfanview.com is a great free graphics program for conversion and viewing especially with all of the so called plug-ins. Under edit, use "show paint dialog". The program can open so many kinds of files which means the directory file filter fails at times. Certain files are part of a class like pdf. You can only do one "undo" function and it's not a graphics program with so called "layers".
     
  8. Muttley600

    Muttley600 New Member

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    Quick scan through, looks like I have lots to learn :)

    I'm accurately measuring by exporting graph & altering lower table to minute detail

    I don't know what I'm doing wrong, I'm getting 2.52799Hz not 25Hz, it's going to be that blinking decimal point again isn't it :-(

    Well, thats me for the night, back tomorrow

    What about my RC calculation?
    Why did I have to put 50ms where you put 5?

    Night both :)
     
    Last edited: Mar 22, 2012
  9. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    Last things first.

    With the timed switch settings "t On" set to 1ms and "t Off" set to 5ms, the trigger trace on the scope just looked like a very brief down-going "spike". It's interesting you chose to extend the "t Off to 50ms ( as I did in subsequent tests) because that gave the scope trace of the trigger pulse a better "definition" in the trace (easier to see).

    For one thing, the answer is 1/4 Hz, which is 0.25 Hz, not 25 Hz. Your off by a factor (multiplier or divider) of 100. So yes, the decimal issue is beating you up. Don't know what to tell you other than to just keep practicing.

    As KISS suggested, I'm going to demonstrate how to use the "Cursor" functions on the scope. These allow for more precise determination of timing (X axis) values.

    The sim "snips" will be posted shortly. (I have GOT to re-boot this machine - slow as molasses in January).
     
    Last edited: Mar 23, 2012
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  10. Muttley600

    Muttley600 New Member

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    On phone for now so spending time looking at differences

    λ means wavelength & is measured in 'm'etres & 1000mm = 1M

    λ is inversely proportional to Frequency (what's the symbol for 'f'?)
    Meaning the exponent numbers go in opposite directions to each other

    So 1Hz = 10 (ex 0)
    1s= 10 (ex 0)

    1KHz= 10 (3)
    1ms = 10 (-3)

    So wavelength is measured over distance
    Frequency measured over time
    No point going into velocity yet as we haven't covered phase

    So again, to get frequency I measure like so:
    1/ (time) = frequency



    Morning (in your time) CBB :)
     
    Last edited: Mar 23, 2012
  11. Muttley600

    Muttley600 New Member

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    Yes, I'm still getting beaten up by decimal point, as you say (hopefully) practise makes perfect

    Got it [​IMG] they say simple things please simple minds [​IMG]

    I was seeing it as 395ms where really it was 3.95s
     
    Last edited: Mar 23, 2012
  12. Muttley600

    Muttley600 New Member

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    Cool, now I now what I'm looking at I can have a play

    Hopefully link below will help you & yes I see my mistake on timing

    No need to beat yourself up, you don't know what your working with this end & thats with me wanting to learn [​IMG][​IMG]

    I know I'll get it in the end, it just may take a while [​IMG]
     
    Last edited: Mar 23, 2012
  13. Muttley600

    Muttley600 New Member

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    Picture it 9 for editing pictures

    I've just been playing with 'paint' in windows 7, you can add text via that as well, so save snip, open it in picture libary, then right click & choose 'edit' (4th line down)
    then you'll find a little 'A' on the left hand side of brushes & hey, voila, ability to add text
     
    Last edited: Mar 23, 2012
  14. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    YES! You've got it!!
     
  15. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Don't use the word over because it can mean divide as in 1 over 4 being 1/4.

    So wavelength is measured in distance units
    Frequency is measured in cycles/s or Hz (or some of the other variants such as MHz or KHz)

    Velocity is just another word for speed, but km/h isn't appropriate. Science uses the kgs (killograms,meters, seconds) system or the cgs (centemeters, grams, seconds) system.
     
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  16. Muttley600

    Muttley600 New Member

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    So I have been relating frequency to ms but really I'd accounted for cycles = t, as in 2∏ = 1Hz but I was seeing 1Hz as 1s


    man, I'm confusing myself now [​IMG]

    ok, lets start again:

    we have three main units we are talking about here: or is that four [​IMG]

    We have - distance/length = λ = wavelength
    cycles/Hz = frequency (is this the ∏)
    phase/speed/velocity = time

    & all this is on the spring opening & closing nothing to do with amplitude because thats relating to VP or ωV


    If that's right, you mean we can tell three different things from this but they all look the same, I'm TRYING not to see them as the same thing........honest I am [​IMG]
     
    Last edited: Mar 23, 2012
  17. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    Very good. Suddenly, you've got it. Very, very good.

    I've been working on the Scope "cursor" demo. This feature is very useful, but not at all easy to explain how to use since there is SO much info displayed and not a little confusing when it it is.

    It does afford a level of precision (for both timing AND amplitude values) beyond what you can get just "eye-balling" the scope face.

    But, truth be told, for all the years I've used scopes (over 53 now, since I was 11), it's only recently (two years ago) that I've had a real (not a virtual sim) scope that has cursors (last CRT type [no cursors] was a Textronix 922A, which was a fantastic machine, but the HV went and for the price of replacement parts I got a hand-held digital type that is a-maz-ing).

    Anyway, again, I have generally used a scope for the "gross", (that is, generally accurate enough) circuit analyses that I perform.

    For instance, "Is there even a signal being generated by whatever I just designed???" "Forget frequency and amplitude!! Is the damn thing even oscillating??!!??"

    For the more accurate real world readings (if I want or need them) I use other instrumentation (digital freq meters, VOMs, and now the digital scope, which, BTW, gives me everything in side bars: Freq, Amplitude, Phase, PP, dB and more,).

    Just my methods. I will (eventually) get around to the scope cursor demo.
     
  18. Muttley600

    Muttley600 New Member

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    I did & have done again, I'll keep reading it until I understand it [​IMG]

    These are my lightbulb moments that keep my desire to learn alive no matter how much I struggle, I will get & TOTALLY understand this, you know we did a comms test run the other day on bikes with external ariel, this has gain numbers etc (at bottom of page)
    I want to be able to understand what this is tellingme, how it is (or isn't) an improvment over the smaller ariel we use, so I shall keep plugging away, I will never give up [​IMG]


    So I can relate F = a time period (be it, hours, minutes, seconds or ms)

    even though you've just told me F is in cycles [​IMG]

    EDIT: got it, it means f=1 (cycle/Hz) / time

    Don't panic, I will get it in the end [​IMG]
     
    Last edited: Mar 23, 2012
  19. Muttley600

    Muttley600 New Member

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    You mean like this

    View attachment 62553 View attachment 62554

    MUTT77 scope sim taken from
    MUTT78 showing cursors measuring XA - XB = DX

    X = width, soory Time/period
    Y = hieght, sorry (whatever it was showing us)
     
    Last edited: Mar 23, 2012
  20. Muttley600

    Muttley600 New Member

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    ok, it gets even more confusing now

    Frequency is equal to velocity according to link

    & was determined in cycles before Hz, no wonder there are so many variations

    but intriguingly exponents are shown as + to frequency & - for λ but surely they are the other way around [​IMG]

    Thats it, I've caught up

    I can see F, wavelength as different things

    so in my ariel attachment 1/2 wave simply means half a radian or half wave

    Does that mean below or above gnd?

    ok, what does 'cos' & 'sin' mean?

    How cool is this [​IMG]
     
    Last edited: Mar 23, 2012
  21. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    I won't be able to say much. On phone. But RADIAN FREQUENCY = 2*PI*f and is denoted by the greek lower case omega.
     

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