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Signal generator using 555 timer

Discussion in 'General Electronics Discussion' started by Terry01, Aug 30, 2017.

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  1. Terry01

    Terry01

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    I built my first signal generator on my breadboard tonight. Its very VERY simple but it'll do for now for something to hook my scope up to when it comes. I can hook a potentiometer into it too so it'll be fun to watch it working and how it changes. I have another 1 from eBay coming that does a wee bit more types of waves and stuff. Only cost a fiver or thereabouts. Once I learn how to use them properly I'll buy a decent one. I know its simple stuff but everyone has to start somewhere. I think my scope should come tomorrow :)
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Good start, Terry, but don't be surprised if your new scope shows a not so ideal signal from the 555. The 555 is a great little bugger but not renowned for cristal clear signals :D

    Your scope will (or at least should) have a calibration output to hook up your probes to and trim (compensate) the phase. Use this first to compensate your probes and to get an idea what a good square wave looks like, then check your 555 circuit. Measure at different points of the circuit, possibly using two probes simultaneously to get a feeling for the different signals around a 555 and how they are related to each other.

    Have fun!
     
    Terry01 likes this.
  3. dorke

    dorke

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    Jun 20, 2015
    Nice start,
    I wonder what scope have you ordered?
    Are you aware of Software Audio Scopes and signal generators that are free on Pcs and Smart phones?
     
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  4. Terry01

    Terry01

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    Jul 5, 2017
    Its a second hand Tenma scope. Just a cheapo for now till I learn how to use one then I'll get a decent one. I got it from eBay so it may well be a banger or maybe not. If its a scrapper I'll have fun with the insides. Once I get it a couple of the guys here have offered to help if I need it so that's good to know. I trust their knowledge and know how. I'm sure that unless its a complete wreck they'll just need a few photos to see it then they'll know what needs fixed. I'm just gathering what I can pick up on here and a couple YouTube channels information wise. I did watch a few channels but have filtered it down to a couple of the best ones.
     
  5. hevans1944

    hevans1944 Hop - AC8NS

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    The usual 1:1 probes do not have (or need) compensation, so don't go looking for an adjustment that isn't there. Check the results pages of this Google search for more information.

    If you did purchase 10X (1:10) or 100X (1:100) probes, these DO have (and require) compensation. A decent "square-like" waveform with fast rising and falling edges is needed. Most bench scopes provide this signal. You simply adjust the compensation variable capacitor, located in the body of the probe, for a "flat top" at the edges with neither overshoot nor rounding. Some probes, such a 1000X (1:1000) high voltage probes, place the trimmer capacitor in a little box with an integral connector for the 'scope.
     
    Terry01 likes this.
  6. Terry01

    Terry01

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    Jul 5, 2017
    My scope arrived today. It looks clean enough and I'm able to get a nice strong crisp trace that runs perfectly along one of the division marker lines so that's good. It was a wide fat trace at first but just needed the focus adjusted a wee bit. Just need my probes to arrive now :)

    I got x10 probes so I'll adjust them too when they come. I'll let you know how I get on.

    Thanks for the help guys.
     
    hevans1944 likes this.
  7. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    No compensation: right. Usual: no In my experience the usual probe is an x10 probe, used for its high impedance. x1 probes are for special cases.

    This may be completely the other way round in the world of radio technology.
     
  8. hevans1944

    hevans1944 Hop - AC8NS

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    I think you have it right, Harald. My "go to" probe, that I usually use on the bench for design or troubleshooting, is a switchable 1X/10X probe. I only use the 1X probe when I need the maximum sensitivity of the 'scope to observe very small signals.

    Some of these switch-selected dual-attenuation probes even have a separate annular pin connection surrounding the BNC on the 'scope, used to electrically advise the 'scope which attenuation factor has been selected, so as to digitally display correctly the volts per division calibration. Nice feature, when it works, and if your 'scope has an alpha-numeric digital display that accommodates the feature. My Tektronix 'scopes are rather old, and only one of them features an on-screen digital display. So I mostly don't need the 'scope to tell me which probe attenuation I am using.

    Good point that the 10X probe also increases the input impedance of the 'scope from (usually) one megohm to ten megohms. This can be very important when probing analog circuits with high circuit impedances.
     
  9. dorke

    dorke

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    Hop,
    more importantly, is the fact that a 10X probe reduces the scop's capacitance by a factor of 10 !
    Probing in high frequency circuits essentially requires a 10X probe.

    An active probe is another issue altogether...
     
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  10. Terry01

    Terry01

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    My probes came today,they have x1 and x10. I've been probing more than I normally do on a Friday! :)

    The scope seems to be working fine and doing as it should. I've been using it most of the day and am picking up how to use it quite quick.

    Happy its a keeper! :)
     
  11. BobK

    BobK

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    Great. You will find getting a scope is something like being blind and getting sight!

    Bob
     
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  12. Terry01

    Terry01

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    Just today I've learned a lot. Mostly familiarizing myself with some of the functions and getting a decent trace each time on the different parts of the circuits. I'll get better and better the more I use it,I'll also learn to understand it more too. Just about everything gives a trace of some kind. I've mostly just been using 1 probe too so I'll get to using both soon,looking forward to that. :)
     
  13. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    We could give you better advice on how to use your 'scope if you would tell us which model Tenma you purchased. There is a huge range of features available on most oscilloscopes, depending on model, but virtually all "modern" 'scopes feature a linear, triggered, horizontal sweep with adjustable sweep rates from microseconds per horizontal division to seconds per division.

    Better 'scopes offer a calibrated horizontal sweep, so if you can display one cycle of the waveform, the time for one cycle can be measured by the length of the sweep from beginning to end of that cycle. The reciprocal of this period measurement is, of course, the frequency of the waveform. Accuracy to about two significant figures is reasonable, so the oscilloscope does not replace a frequency counter but it does get you into the ballpark in terms of measuring frequency.

    Very important to triggered-sweep oscilloscopes is the accuracy and stability of the trigger settings. Very seldom will you be interested in just one or more complete cycles of a waveform. Instead, you would like to inspect a short time interval of the waveform, one that is particularly important to your circuit operation. This means your trigger must occur very near the beginning of the interval you want to inspect. Often the only way to accomplish this is to use a delayed trigger. A repetitive point on the waveform is used to initiate the delay. After the expiration of the delay interval, the actual sweep (the portion displayed on the CRT) is either triggered immediately or it is triggered according to your selected criterion of amplitude and slope (positive or negative) of the waveform.

    It can get a lot more complicated, but that should be enough for your consideration right now. Tell us the model number of your 'scope and what you expect to "see" with it. As @BobK said in post #11, using an oscilloscope is like suddenly gaining sight after being blind. It opens up a vast array of test procedures that simply cannot be accomplished in any other way. I use my 'scopes more often than my multimeter, although both have a place on my bench. Oscilloscopes "look" at the dynamics of circuit operation, while other devices mostly are useful only for examining steady-state conditions.
     
  14. Terry01

    Terry01

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    Its a Tenma 72-6815. I was looking online for a user manual for it but can't find one. You can look every function up on google or ask the guys here and find out what it does and means but I'd rather have the user manual for that machine. I'll just be using it for looking over hobby stuff I build and things like that,nothing meaningful yet. It will depend too on how much I end up learning in the future.
     
  15. dorke

    dorke

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    You can get the User Manual of the Tenma 72-6800 here ,similar model (20MHz).
    You can also contact the company for the exact User Manual.
    The scope is analog, a very basic model.
     
  16. BobK

    BobK

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    Which is what I would recommend for a beginner. DSOs are tricky to use, though far more capable, especially for capturing one time events.

    Bob
     
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  17. dorke

    dorke

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    Bob,
    In general I agree with you.
    It is basically a "definition of needs" and price.
    I have the classic ("legendary") Tek 465B which I got for about 50$.

    A DSO is a must for nowadays applications, non-repetitive signals, single shot events.
     
  18. BobK

    BobK

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    Perhaps what is needed is an analog mode on a DSO so beginners could start with that.

    Bob
     
  19. Terry01

    Terry01

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    Jul 5, 2017
    I bought this one because I am very new to electronics,like VERY new. I've had a go at soldering and although I'm no master I can solder so I'll just get better as I learn more and solder more. I got myself half a dozen mixed boxes of components. Its been good fun googling them and sort of learning as I read more. I've been watching stuff on YouTube and Hila Science and picking up what I can on here. I'm learning bits and pieces and find it very interesting. Its purely a hobby for me,just for fun and something to do. I'm very happy with what I've learned and looking forward to learning more. I have no interest in studying to deadlines or whatever. I sit at my desk and try things out or whatever and as soon as I get fed up I put the tools down till tomorrow. I love it that way. I could have went and spent £1000 on a scope but I'm still very capable of frying it doing something "silly". If I cook this one I'll have fun trying to fix it and if I can't I'll get another no sweat. If I cook £1000 worth that would piss me off and it wouldn't be fun no more. Once I learn how to use this one properly and am fluent using it the odds are I will spend a bit more on a digital one. I like the fact I have to take 5 mins to set this one up too and work out whats on the screen. I think that'll set me in good stead too for when do get a digital one. I'll prob just use this one for 6 months or so then maybe think about going digital. :)
     
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