Why 1 million ohms resistors?

Discussion in 'General Electronics Chat' started by brucester, Dec 24, 2012.

  1. brucester

    Thread Starter New Member

    Dec 24, 2012
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    Hi,

    I am putting together a simple kit i bought from a local electronic shop.

    My question is, why does it have a 10M resistor and 2 1M resistors when only a 9 volt battery is used?

    What is their purpose in circuits with such small power sources?

    What components use 0.00000009 amps?

    Thanks :)

    oh, and merry christmas :)
     
  2. Metalmann

    Active Member

    Dec 8, 2012
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    Merry Christmas back at you, and I hope you get your money back on that kit.

    Happy New Year!:D
     
  3. MrChips

    Moderator

    Oct 2, 2009
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    There are millions of circuits that run on microamps
    such as clocks, cellphones, cameras, computers, etc. etc.
     
  4. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    Why would you want the OP to return a kit because of 2 15 cent resistors that the OP may or may not be able to use?
     
  5. brucester

    Thread Starter New Member

    Dec 24, 2012
    19
    0
    The circuit actually uses them and it works well. I was just wondering what their purpose was.

    This is the kit i built, took about an hour to solder together: http://www.jaycar.com.au/productView.asp?ID=kj8224

    It basically creeks like a cricket and flashes its led eyes whenever it hears a sound
     
  6. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    Congratulations! Keep it up. Eventually you should consider looking at micro controllers. A lot of cool things you can do with them.

    .
     
  7. dataman19

    Member

    Dec 26, 2009
    136
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    So,
    Looking at the cricket kit link...
    The link answered your question......
    ..
    This circuit is a micro amp circuit....
    ..
    Hence, all the resistors...
    ..
    Oh yea - Merry Christmas everyone...
    ..
    Dave
    Phoenix, AZ
     
  8. JingleJoe

    Member

    Jul 23, 2011
    185
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    As it is becoming aparent from previous posts, the answer is very simply; some circuits don't require more power than that to operate. Some can work from a tiny few microamps. :) That's modern tech for you!

    P.S. the topic title was really misleading :rolleyes: you mean 1 million ohms, not 1 million resistors :D
     
  9. WBahn

    Moderator

    Mar 31, 2012
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    You should have included this additional information (about the kit) in your first post. I originally read your post as though you were assembling a generic electronics kit, meaning creating a collection of parts for use in future projects, and were wondering why a generic resistor kit included such high value resistors. The fact that you were talking about a specific project kit casts a completely different light on it.

    For battery powered applications, you want to design the circuits to draw as little power as possible and, given the emphasis in recent years on battery-powered devices (think smart phones, cameras, iPods, etc., etc.) there are now many, many ICs out there that draw fractions of a microamp, at least in certain modes. Similarly, there are many discrete circuits you can design and build that use comparable current levels. So 10MΩ resistors are not at all unreasonable to see in 9V circuits.

    As for what they are being used for in this particular kit... well, we'd need to see the schematic to have a chance at making a reasonable guess at that. My not-necessarily reasonable guess is that they might be being used in a voltage divider to set a threshold level that the signal from the microphone has to rise above in order to activate the cricket.

    Oh, and try to come up with better thread names. I was expecting this to be a post about why there are a million different values of resistance or something like that.

    Welcome aboard and Merry Christmas!
     
  10. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I have adapted the title of the thread for better understanding.

    Bertus
     
  11. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    Sort of like the title for my two books I would like to write.

    "Million Dollar Ideas". A book of ideas worth a million dollars.

    And

    "Million Dollar Ideas" (emphasis on the word dollar) . A book of a million ideas but each only worth a buck. :)
     
    absf and shortbus like this.
  12. Metalmann

    Active Member

    Dec 8, 2012
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    I thought he was jokingly referring to a bad kit.;) And, Merry Christmas!
     
  13. nigelwright7557

    Senior Member

    May 10, 2008
    487
    71
    Designers tend to use larger resistors to save on batteries.

    1M isn't a bad value. However a friend of mine used 10M in some telecoms equipment then found it failed in hot climates where the air was humid !
    They had to install air conditioning to make the equipment work !
     
  14. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Can you tell me how does a value relate to reliability here? The manufacturer and type yes, but linking failure due to humidity to resistor value is nonsense.
     
  15. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    No it was actually common in the old days of carbon resistors.

    High value resistors were very unreliable, especially with moisture and/or high voltages.

    We're very spoilt these days with modern metal film resistors etc.
     
    #12 likes this.
  16. JingleJoe

    Member

    Jul 23, 2011
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    Old resistors age like a fine wine, getting stronger with time.
     
  17. #12

    Expert

    Nov 30, 2010
    16,261
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    Yes, RB is right. Back in the tube days, any resistor over 100k ohms would drift upwards in value over time. Measuring and replacing all the high value resistors was as common as replacing the leaky electrolytic capacitors.
     
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