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Help amplifying a circuit — Parallax Forums

Help amplifying a circuit

SONIC the HedgehogSONIC the Hedgehog Posts: 321
edited 2012-08-28 18:14 in General Discussion
I've been experimenting alot with computer architecture, and I needed a clock, but I don't have the resistors necessary to build an astabke circuit on a 555 timer to suit my needs, so does anyone know how to amplify a crystal oscillator? Any help or insight is appreciated!

Comments

  • Dr_AculaDr_Acula Posts: 5,484
    edited 2012-08-27 17:14
    You mean like these sorts of circuits? http://www.z80.info/uexosc.htm

    How fast do you want this to go. 555 are good up to hundreds of kilohertz. Xtals - probably the slowest is going to be 1Mhz.
  • kwinnkwinn Posts: 8,697
    edited 2012-08-27 17:30
    Dr_Acula wrote: »
    You mean like these sorts of circuits? http://www.z80.info/uexosc.htm

    How fast do you want this to go. 555 are good up to hundreds of kilohertz. Xtals - probably the slowest is going to be 1Mhz.

    Unless you use a 32KHz watch crystal.
  • Dr_AculaDr_Acula Posts: 5,484
    edited 2012-08-27 17:42
    Hey, cool idea re the watch xtal. And of course, that is 32768hz which divides down to 1 sec as it is a power of two.
  • kwinnkwinn Posts: 8,697
    edited 2012-08-27 17:58
    They are very handy for low power consumption projects that need very little in the way of cpu processing power.
  • SONIC the HedgehogSONIC the Hedgehog Posts: 321
    edited 2012-08-27 18:00
    That's perfect thanks! I was hoping to try and get up to 160mHz.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2012-08-28 09:10
    A 555 will never get to 160Mhz. In fact you will be hard pressed to find a crystal anywhere near a fraction of that. I have a few 75Mhz and I think one 80Mhz crystal controlled oscillator. Maybe there is a way to double the frequency.

    Seems a bit odd to not have resistors. They are very cheap.

    Frankly, the problems with a stable 160Mhz oscillator are challenging. First, it is a very fast frequency. And then, if this is a square wave with any power you might be generating a lot of harmonic noise that will upset someone.

    And of course, what kind of chips are you going to be able to connect with? That is quite fast for homebrew.
  • RDL2004RDL2004 Posts: 2,554
    edited 2012-08-28 09:47
    You can get pre-built oscillator modules that get up to that frequency. They use a crystal along with a PLL, and they're not cheap. Maybe you could build one yourself that would be less expensive but still adequate for your needs.

    www.mouser.com/ProductDetail/ON-Semiconductor/NBVSPA024LNHTAG/
  • ercoerco Posts: 20,259
    edited 2012-08-28 09:53
    Dr_Acula wrote: »
    Hey, cool idea re the watch xtal. And of course, that is 32768hz which divides down to 1 sec as it is a power of two.

    But at 15 for a buck, they are prohibitively expensive, almost as much as a resistor! :)

    http://www.ebay.com/itm/15x-Seiko-32-768KHz-WATCH-CRYSTAL-32-768-32-KHz-SMD-SMT-/271029538031?pt=LH_DefaultDomain_0&hash=item3f1a9e8cef
  • Mark_TMark_T Posts: 1,981
    edited 2012-08-28 10:30
    SONIC the Hedgehog wrote: »
    I've been experimenting alot with computer architecture, and I needed a clock, but I don't have the resistors necessary to build an astabke circuit on a 555 timer to suit my needs, so does anyone know how to amplify a crystal oscillator? Any help or insight is appreciated!

    For frequencies around a few MHz you can try the standard CMOS inverter oscillator. String an _odd_ number of inverters (try 3 to start with) head to tail (not schmidt triggers though), and feedback from the last to the first with a 1M resistor in parallel with a xtal. Add capacitors around 22pF to ground at each end of the crystal. The CD4049 hex inverter can be used. Lower frequencies need more inverters (the propagation delay needs to be about 1/2 the oscillation period I think). Take the output from the middle of the string if possible (ie not just a single inverter) to reduce frequency-pulling effects? Buffer the output with a 74HC gate for more current-driving capability and faster edges.

    For higher frequencies the 74HC series can be substituted I suspect. 74HC04 hex inverter for instance (any NOR or NAND gate can be configured as an inverter of course if one's lying around unused).

    If the oscillator circuit wants to run faster than the crystal it may excite an overtone of the xtal, which will about 3 or 5 times the nominal frequency (not exactly though). Add more inverters or more capacitance to tame this.
  • localrogerlocalroger Posts: 3,452
    edited 2012-08-28 12:11
    Dr_Acula wrote: »
    Xtals - probably the slowest is going to be 1Mhz.

    They're not very common any more but I have a small pile of 100 KHz crystals from Radio Shack vintage PBox frequency marker kits, which I cleaned up for $1 apiece when RS discontinued the PBox line.
  • SONIC the HedgehogSONIC the Hedgehog Posts: 321
    edited 2012-08-28 17:34
    I don't think that speeds 100% important, I'm really building a simple memory module to play around and experiment with, but I didn't have a clock set up and was questioning the 555 vs an actual crystal.
  • SONIC the HedgehogSONIC the Hedgehog Posts: 321
    edited 2012-08-28 17:52
    Oh and about the resistors, I didn't have the kinds I think I needed on me, nor did I feel like going to the local radio shack.
  • Dr_AculaDr_Acula Posts: 5,484
    edited 2012-08-28 18:10
    I'm really building a simple memory module to play around and experiment with

    Is that going to be running at 160Mhz? Or do you want to debug it at a slower frequency (I've someones clocked chips once every 10 secs for debugging). And of course, rather than building 555 timers or xtal oscillators, you can always use a Propeller chip to create the clock and then program the speed in software. No resistors needed for that :)
  • SONIC the HedgehogSONIC the Hedgehog Posts: 321
    edited 2012-08-28 18:14
    Dr_Acula wrote: »
    Is that going to be running at 160Mhz? Or do you want to debug it at a slower frequency (I've someones clocked chips once every 10 secs for debugging). And of course, rather than building 555 timers or xtal oscillators, you can always use a Propeller chip to create the clock and then program the speed in software. No resistors needed for that :)
    That's actually what I'm leaning towards right now as I already have a nice square wave program ready to use, but I'd have to set up my propeller. I also want to to expand this project and finished the alu I started, do I figure memory is a nice and easy start.
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