Help! Cant get 555 Timer tuned to 38kHz

LifedriveLifedrive Posts: 8
edited December 2009 in BASIC Stamp Vote Up0Vote Down
hi guys,

currently i'm building the infrared object detection sensor with reference from Parallax "Experiment #4: Infrared Object Detection".

I supposed to get the oscillator circuit·tuned to 38000Hz frequency, but the max value i get is only·about 11000Hz with the 1K pot adjusted to zero resistance. If i tuned the resistance higher, the frequency will drop lower.

I already checked the circuit according to the Figure 4.1 in that article,·using all the required components.

Really appreciate if anyone can help.

Thanks

·

Comments

  • 12 Comments sorted by Date Added Votes
  • DufferDuffer Posts: 374
    edited December 2009 Vote Up0Vote Down
    This might help: http://www.robotroom.com/Infrared555.html (and others) from Google search "555 timer 38KHz"

    Duffer
  • m.r.b.m.r.b. Posts: 36
    edited December 2009 Vote Up0Vote Down
    Slightly 'off topic'... But relevent, to your generation of a 38Khz carrier...

    I have had problems in the dim and distant past generating an accurate 38KHz signal (long before I discovered Prop chips!!!)
    (I used a 38Khz signal, for·stereo sub-carrier generation·for an MP3 player FM stereo low power modulator I made from scratch)


    Can I suggest the 'realitively·low fuss' method I used...

    Build·a crystal oscillator based around a couple of inverting CMOS logic gates (NOT, NAND/NOR etc with inputs tied together)...
    Buy a·38KHz crystal·(or two, they are quite electrically delicate!!)

    Try a web search for something like '38KHz crystal'··· or 'Crystal·BA1404'... you will find a whole bunch of suppliers.
    These crystals are usually in the "watch crystal" can style....


    Hope this has helped...

    Mathew...
  • VANITYVANITY Posts: 6
    edited December 2009 Vote Up0Vote Down
    LifeDrive,

    I've been trying to interface a 555 with a BS2 today and just got it going. I'm using an LM555 in A-stable mode to act as a sort of coded interrupt which will then keep track of time inside the BS2.

    I not sure what that circuit looks like, but maybe this helps:

    If you're using it in A-stable mode (square wave mode) then you should try lowering your capacitor as low as possible (try a 0.5 mf). It might not be safe for the chip to lower the discharge and threshold resistors lower than 1000 ohms, but you could try that too.

    I'm not sure about the mono-stable mode (pulse spurt mode), but you probably don't want to use this because your duty cycle will probably be too small.

    Check out this link:

    http://home.cogeco.ca/~rpaisley4/LM555.html
  • ercoerco Posts: 18,498
    edited December 2009 Vote Up0Vote Down
    Post your circuit.

    Probably·an assembly or component value error. The 555 is proven, reliable and bulletproof. It will output 200 mA, so it's hard to kill! Double check everything! When in doubt, rip it apart and start over. Use a solderless breadboard·to git 'er done·and verify function first,·only then solder it up.

    A very useful 555/556 site: http://www.kpsec.freeuk.com/555timer.htm

    Here's·my article·showing a 556 circuit that modulates the·underlying 38 khz carrier: http://www.botmag.com/articles/scribbler.shtml·This circuit is more useful than a 555 timer emitting an unmodulated 38 khz carrier.




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    ·"If you build it, they will come."
    "When you make a thing, a thing that is new, it is so complicated making it that it is bound to be ugly. But those that make it after you, they don’t have to worry about making it. And they can make it pretty, and so everybody can like it when others make it after you."

    - Pablo Picasso
  • LifedriveLifedrive Posts: 8
    edited December 2009 Vote Up0Vote Down
    Hi

    1st for all, Thanks for all the replies...

    I did try the suggestion from Vanity :

    Quote "If you're using it in A-stable mode (square wave mode) then you should try lowering your capacitor as low as possible (try a 0.5 mf). It might not be safe for the chip to lower the discharge and threshold resistors lower than 1000 ohms, but you could try that too. "

    I·managed to achieve the·38Khz··by reducing the 1000ohms resistor to 220ohms, haven't try change the capacitor as i dont have it at home. Will give it a try when i've·the capacitor as Vanity did mention lowering the resistance might not be safe for the chip.

    Yeah those websites suggested i find it very useful, actually i'm trying so hard to get a better understanding as· i'm quite new into this.

    By the way, i'm·using Stamp BS2p24 with lynxmotion Bot-board II.
  • I'm looking at getting 38k crystals for my ir project...m.r.b mentioned building a crystal oscillator based around a couple of inverted cmos logic gates. How does that work...does anyone have a schematic?
  • dr hydra wrote: »
    I'm looking at getting 38k crystals for my ir project...m.r.b mentioned building a crystal oscillator based around a couple of inverted cmos logic gates. How does that work...does anyone have a schematic?

    The HEF4069 and HCU04 data sheets usually have Crystal Oscillator examples
    eg

    https://assets.nexperia.com/documents/data-sheet/HEF4069UB.pdf
    https://assets.nexperia.com/documents/data-sheet/74AHCU04.pdf

    At 3v3 there is usually too much gain on the HCMOS parts for sub 40kHz, so I'd try the values given in Table 8. External components for resonator (f < 1 MHz) of the AHCU04 data, on the HEF4069 device.
    or you can try reducing the Vcc on the AHCU04.

    You probably need 3 gates, - the inverter/osc and then two stages to square things up.
  • Remember that breadboards can add capacitance where you don't expect it -- this might be affecting your results.
    Jon McPhalen
    Hollywood, CA
    It's Jon or JonnyMac -- please do not call me Jonny.
  • There's no hyphen in the word "astable". It's not type A stability, but rather instability: it is astable, "a-" (not) "stable". Instead of just settling in some stable state, it oscillates between two states, without ever settling on one.
  • This thread is as old as my twins. I'm still a fan of using 555/556 timers for generating 38 kHz signals. Simple & quick to build and very stable frequency output even if the supply voltage changes.

    555 timers are cheap & retro. Just like me.
    "When you make a thing, a thing that is new, it is so complicated making it that it is bound to be ugly. But those that make it after you, they don’t have to worry about making it. And they can make it pretty, and so everybody can like it when others make it after you."

    - Pablo Picasso
  • jmgjmg Posts: 10,617
    edited October 27 Vote Up0Vote Down
    erco wrote: »
    This thread is as old as my twins..

    Yes, dr hydra should really have started a new thread, as he asked about 38kHz Oscillators mentioned contents, not the title...
    Maybe the thread can be split ? ... 32/38kHz osc does come up on rare occasions.
  • Isn't the most obvious answer to the top post that the problem you can't go higher is simply that you have the wrong cap in the circuit? Either it's the wrong value, wrong type, faulty, but obviously you need a smaller value.
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