1Hz Timebase from Wall Wart

Discussion in 'The Projects Forum' started by franklinmknight, Jan 12, 2010.

  1. franklinmknight

    Thread Starter New Member

    Jan 3, 2010
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    Ok, so I've been doing some research and I'm unable to find anything reliable; it appears that all the helpful sounding links no longer exist. From what I understand is that when you rectify 120VAC from the fall the 60Hz signal doubles to 120Hz; I think it's only through half-wave rectification. For my school project I'm only allowed to use DC, no AC; aside from a wall wart. So does a wall wart really generate the 120Hz signal and what is the easiest and way to divide that to 1Hz?

    Also, if possible please include links and/or schematics; helps with the learning process. :)

    Thanks all in advance.
     
  2. jgessling

    Active Member

    Jul 31, 2009
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    There are many kinds of wall warts. Some put out AC. You could use one of those and get your time base from that. Look at Howstuffworks and search for digital clock for a example circuit.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    When you perform half-wave rectification, one polarity of the wave is simply lopped off; you just get (very) rippled DC, either the positive or negative component of the sinewave, at the same frequency that the input was.

    If you perform full-wave rectification, you get rippled DC at twice the input frequency.

    Whether you get rippled DC or not depends on your particular wall-wart. Many have poor or non-existent regulation, others are actually quite good. I just looked at a wall-wart I had sitting around; just a 4v 200mA unit. I was a bit surprised to see that it had no detectable ripple on it's DC out - of course, that was with no load applied.

    As far as 1Hz timebases, find ONsemi's datasheets for the MC14040B and MC14060B. You can download them directly from http://www.Onsemi.com
    The former has schematics for use with crystals and 60Hz input, the latter has schematics for use with crystals and other ideas.
     
  4. franklinmknight

    Thread Starter New Member

    Jan 3, 2010
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    Would you happen to know anything about the 555/556 timer method? I don't know if it's any better or worse than the suggestions previously listed.
     
  5. CDRIVE

    Senior Member

    Jul 1, 2008
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    Was your instructor specific about the required accuracy and stability of the time base? If it's not critical you could easily build an astable 555 time base generator.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    555/556 timers are convenient and cheap if you don't require accuracy. However, they are woefully inadequate for any sort of timekeeping purposes. Even crystal timebases will wander several seconds per day if they are not compensated TCXO's (temperature compensated crystal oscillators) are more stable, and OCXO's (oven-ized crystal controlled oscillators) are more stable yet. Those are just a few types, there are many more.
     
  7. franklinmknight

    Thread Starter New Member

    Jan 3, 2010
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    At this point in time I'm not all that worried about accuracy. I'm running short on time and need a simple, cheap, and relatively fast approach. So if yall consider this the best approach for my situation, can I get some more information? Google must have changed because I can no longer find reliable information.
     
  8. CDRIVE

    Senior Member

    Jul 1, 2008
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    Since you don't appear to need great accuracy or stability, what are you going to drive with the time base?
     
  9. Wendy

    Moderator

    Mar 24, 2008
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    Adding to CDRIVES question, what logic family? Does it need to be a +12V to ground square wave (think CMOS) or 4.5V to ground (TTL)?
     
  10. CDRIVE

    Senior Member

    Jul 1, 2008
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    Adding to the comments Sgt.Wookie posted regarding varying degrees of stability and accuracy of crystal time bases:

    Many years ago, before we had many of the specialized chips available to us now, a ham designed a freq counter employing a receiver front end tuned to WWV. Most of his circuitry was discrete at that time. He used the WWV signal to control a phase locked loop that in turn kept the on board 10MHz crystal osc. locked to to the carrier. No ovens!

    Really great for those living in Fort Collins Colorado as they wouldn't need much of an antenna. :D
     
  11. t06afre

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  12. KMoffett

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  13. franklinmknight

    Thread Starter New Member

    Jan 3, 2010
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  14. retched

    AAC Fanatic!

    Dec 5, 2009
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    if you need a 1 hz time base- less accuracy, in a hurry, go to a dollar store or craft store and get yourself clock guts. The made in china clockworks have a ceramic 1hz resonator in them.. You probably have one in the house. The clockworks are the ones used to make a photo into a clock..
    EVEN if they say QUARTZ, if they also say MADE IN CHINA, they are ceramic resonators.

    [ed]
    Here you are. I found a website that shows you exactly how to do what I was suggesting.
    http://josepino.com/?one_second_timebase
     
    Last edited: Jan 13, 2010
  15. jgessling

    Active Member

    Jul 31, 2009
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  16. Mike33

    AAC Fanatic!

    Feb 4, 2005
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    Simple, cheap and fast method to get 1Hz is to use a 555, ayuh! Depends on what you need to do with the 1Hz signal (what are you driving?)...do you need to get it from the walwart, or ANY way at all? The 555 will do this quite well for 'school project' purposes, but as stated above, accuracy will suffer a bit. Good for flashing an LED about 1x per second, tho! My thoughts here are based on availablity (Radio shack...) and speed of construction, plus the ability to tweak the circuit (learning and using for other applications).
    So possibly tell us more about the project, why you need the 1Hz, and are you restricted in what you can use?

    ~Mike
     
  17. beenthere

    Retired Moderator

    Apr 20, 2004
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    Half wave rectified is really DC. The pulsations don't cross zero, so it's no longer AC.
     
  18. t06afre

    AAC Fanatic!

    May 11, 2009
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    Also remember that a wall warts do come in many shapes. AC,unstabilized DC, and stabilized DC. If you use a wall wart as timing source only a pure AC wall wart will be useful in your project. I think as a very good rule thumb of thumb. The unstabilized DC type is equipped with some sort of filter capacitor. Hence it can not be used as timing source. Please correct me if I am wrong on the latter ;)
     
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