teach me about crystals

Discussion in 'General Electronics Chat' started by vortmax, Nov 20, 2012.

  1. vortmax

    Thread Starter Member

    Oct 10, 2012
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    I'm building an interface circuit for a Wii camera which requires a 25 MHz clock signal. The plans I found online show the crystal/capacitor group I'm used to, but it also adds a resistor and a hex inverter.

    What is the purpose of adding the hex inverter? Do I actually need it? I don't really have enough room on my board to easily fit the IC and other components.

    I should also add that I'm interfacing with a 3V3 mcu, so I don't need to do the line level conversion included in the plans I linked to....also all of the 7404's I have access to are 5V logic, so leaving it out would make my life MUCH easier.
     
    Last edited: Nov 20, 2012
  2. takao21203

    Distinguished Member

    Apr 28, 2012
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    use a canned crystal osc. That could be SMD, or a regular one, which you place above the other components.
     
  3. Audioguru

    New Member

    Dec 20, 2007
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    Instructables are usually "designed" by little kids (some are only 10 years old) who know nothing about electronics. You found one in a foreign language.

    An oscillator must contain an amplifier (the inverter) that amplifies the input which is its output then the signal goes around and around.

    Buy a 25MHz oscillator instead that is much smaller.
     
  4. MrChips

    Moderator

    Oct 2, 2009
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    What MCU?
    Most MCUs already have a crystal oscillator circuit built in. Just add the crystal and two capacitors.
     
  5. vortmax

    Thread Starter Member

    Oct 10, 2012
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    Yea I know not to trust instructables. There are a few sources floating around the web, all based on the original Japanese blog post where they guy reverse engineered it. It's all that same basic circuit.

    The mcu is an MSP430G2553. The data sheet says it can only handle up to 16 MHz, which isn't high enough.

    Looking at as an amplifier circuit, it does make sense why the hex inverters are there. I might just have to break down and order some oscillators. So much for attempting to use what I had lying around.

    thanks guys
     
    Last edited: Nov 20, 2012
  6. ScottWang

    Moderator

    Aug 23, 2012
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    A circuit needs a clock oscillator to run, it seems as a human needs a heart to pushing the blood circulation, and to keep our body to be safe and alive.

    Many ways to generate a clock to run, in your circuit that you need a crystal clock oscillator, you can use as the circuit shows the crystal, cap, resistor, 74hc04, or to buy a module that already made up a crystal clock oscillator, and the appearance as below:

    The Golledge range of Clock Oscillators.
    http://www.golledge.com/docs/products/clockosc.htm?gclid=CKzU7_mK37MCFQtZpQodiygArQ

    You also can DIY as below to compress the size.
    Make your own crystal oscillator.
    http://members.iinet.net.au/~davem2/overclock/osc.html
     
  7. MrChips

    Moderator

    Oct 2, 2009
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    So you're trying to push a part to 25MHz when it is designed for 16MHz.

    Good luck with that.
     
  8. takao21203

    Distinguished Member

    Apr 28, 2012
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    Investigating that website a little further I can only say: OMG.

    If you need crystal OSC, ebay, Futurlec, Farnell, RS Components etc. all have them. They are cheap standard components so why bother?
     
  9. vortmax

    Thread Starter Member

    Oct 10, 2012
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    The camera has built in DSP. It does "blob" isolation and will spit out the position and size of up to 4 objects at 100Hz over I2C as a slave. The 25Mhz clock is for the internal mcu and not for communication with the external mcu. The mcu I'm using to read the camera will be running well within its tolerances as the I2C master.

    I know I can buy one, but I was trying to use parts I already have so I could start coding over the holiday weekend and not spend $5 in shipping for a $2 part.
     
    Last edited: Nov 20, 2012
  10. takao21203

    Distinguished Member

    Apr 28, 2012
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    I have many 18 MHz canned oscillators here that costed me less than 50c each.

    When I needed 12 MHz crystals (for USB), I placed a 50 dollars orders, not all of that components I need immediately, but it's good to have a 100pcs. brick around with brand new bargraph displays :)
     
  11. vortmax

    Thread Starter Member

    Oct 10, 2012
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    haha, yea... I'm slowly building up my personal stockpile of parts, so I have used that excuse a few times recently. I think my wife would kill me if she saw another mouser bill on the CC statement.
     
  12. ScottWang

    Moderator

    Aug 23, 2012
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    I'm not tell him to buy anything from that web, it just tried to shows that how the crystal oscillator module look like.
     
  13. takao21203

    Distinguished Member

    Apr 28, 2012
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    Sometimes when I see people hoarding computers, I wonder where they obtain all that money. 10000s of $! And I wonder what this shall be good for.

    I always examine websites into all nooks and crannies.

    http://members.iinet.net.au/~davem2/amiga.html

    So, this guy is a *hoarder*. Among other things.
     
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