What is this resistor for?

Discussion in 'General Electronics Chat' started by peck68, Mar 24, 2010.

  1. peck68

    Thread Starter Member

    Nov 27, 2009
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    I don't really have a 15M resistor - i don't even think the shop even sells them either...

    [​IMG]
    http://www.reuk.co.uk/Making-Very-Accurate-Timers.htm

    That 15M resistor just left of the timing crystal, what is it for? Is it possible to just go up to 10M? (since i have 10x 1M)
     
  2. retched

    AAC Fanatic!

    Dec 5, 2009
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    I believe they are dividing the crystal down to a 2hz timebase

    You can use your 10M and a 5M in series.
     
  3. peck68

    Thread Starter Member

    Nov 27, 2009
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    But then that would dwarf the 330k resistor? Im not even sure what that is used for lol :confused:

    Silly question of me but I haven't used crystals before, but why do i even need resistors in that section? Surely the crystal isnt going to produce a whopping current

    Looking here:
    http://www.electronics-tutorials.ws/oscillator/crystal.html
    [​IMG]

    The crystal is just connected directly to the chip (even though it is a microprocessor, a 4060 still has the same inputs - ish)
     
    Last edited: Mar 24, 2010
  4. Von

    Active Member

    Oct 29, 2008
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    I believe it is to reduce any voltage differential across the crystal. Such voltage can lead to aging and reduced lifetime.
     
    Last edited: Mar 24, 2010
  5. retched

    AAC Fanatic!

    Dec 5, 2009
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    Its how the 4060B takes the pulses. The difference between pins 10 and 11 set the 4060B count speed.
     
  6. peck68

    Thread Starter Member

    Nov 27, 2009
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    Soo... It is a definite 15M then? Or a mis-type as retched said earlier?
     
  7. retched

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  8. peck68

    Thread Starter Member

    Nov 27, 2009
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    Darn it - anyway thanks for the help
     
  9. retched

    AAC Fanatic!

    Dec 5, 2009
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    What are you trying to do, I may be able to help.

    You can add up a bunch of resistors to = 15M..It doesn't have to be 1
     
  10. peck68

    Thread Starter Member

    Nov 27, 2009
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    Oh I was just making a 1Hz clock generator - looking through my parts bin I realised I had not a resistor above 1M ;)

    However on Maplins there is a 10M, 3M9 and a 1M resistor, I do have a 100K though - I could just couple them all together and get it that way as you said

    I only made this topic to see if there was a way round me buying even more stuff :rolleyes:
     
  11. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    I think the only conceivable purpose for that is static discharge.

    eric
     
  12. SgtWookie

    Expert

    Jul 17, 2007
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    The 15M value is not terribly critical.
    Try it with 5M and see if it works.

    The point of it is to make certain that the oscillator starts. Without that resistor, the oscillator could get "stuck" on start-up.
     
  13. redlight000

    Member

    Feb 26, 2010
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    Hi Peck68,
    Just out of interest what does that circuit do.... and its use?

    cheers
    redlight000
    :D
     
  14. SgtWookie

    Expert

    Jul 17, 2007
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    It divides the 32768Hz xtal frequency down to a 1-second pulse. Very useful for clock projects.
     
  15. JDT

    Well-Known Member

    Feb 12, 2009
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    The 15M resistor is there to bias the CMOS gate that is used as a crystal oscillator. The value is not critical. High as possible but 10M will work OK.
     
  16. Wendy

    Moderator

    Mar 24, 2008
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    Actually it is 2 Hz minimum. You need another external flip flop, but other than that I agree totally with Wookie, including the try alternatives and see if it works.
     
  17. peck68

    Thread Starter Member

    Nov 27, 2009
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    Shouldnt need to? The 2Hz is divided by 2 to make 1Hz? Anyway

    I cant understand why my led isn't lighting :( i tried it with just the 4060 to get it to flash every 0.25 secs - yet its not even lighting up at all :confused:

    Is it a dud CMOS or crystal? I am using a 10M resistor instead of 15 by the way

    ---

    Edit: Ahaaa, sorry i am so stupid :D

    Had the resistor that connects the led a row below it (i keep doing this with breadboards) so it wasn't getting any power

    Flip flop works good by the way, no need for another one (unless i want 0.5hz)
     
    Last edited: Mar 25, 2010
  18. Wendy

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    Mar 24, 2008
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    Show us how your doing it (a schematic). CMOS doesn't drive LEDs very well, you'll need something like this...

    [​IMG]

    It is also entirely possible that your oscillator isn't oscillating.
     
  19. peck68

    Thread Starter Member

    Nov 27, 2009
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    No it does work now - just didn't have it connected up properly ;)

    [​IMG]

    (except its a 10M resistor instead of 15, and those 1k resistors are 10k)
     
    Last edited: Mar 25, 2010
  20. Wendy

    Moderator

    Mar 24, 2008
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    How did you wire it up? I betting not a protoboard, but I would be interested if I were wrong.
     
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