Digital Electronics Oscillators Help

Discussion in 'The Projects Forum' started by ExpL0siV3Man79, Aug 8, 2018.

  1. ExpL0siV3Man79

    Thread Starter Member

    Jun 4, 2018
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    I am trying to make a short distance transmitter and receiver using logic gates , 555 timers , Capacitors , OpAmps and Crystal Resonators . I know how to make a transmitter with 555 timer (square wave) it transmits Morse code at a frequency of around 24kHz but I can't make a proper receiver of my own . Any idea for a circuit? I really don't know what to do ...
     
  2. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    Interesting nickname.
     
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  3. crutschow

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    Mar 14, 2008
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    Is this over the air or over wire.
    How does the 555 send the Morse Code?
    How is the 24kHz modulated?
     
  4. danadak

    Well-Known Member

    Mar 10, 2018
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    Google "vlf amateur radio", tons of stuff out there
    on VLF.

    Regards, Dana.
     
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  5. ExpL0siV3Man79

    Thread Starter Member

    Jun 4, 2018
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    Well I googled it but found nothing for more that 9kHz . For the transmitter I used a 32.768kHz crystal to generate the carrier wave . I have 2 of these crystals . Can I use the second one to make a low pass filter for the receive and then lead the signal to an amplifier ?

    Also can I use an NE555 timer chip to filter out all the other frequencies from the receiver?
     
    Last edited by a moderator: Aug 9, 2018
  6. bertus

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    Apr 5, 2008
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  7. ExpL0siV3Man79

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    Jun 4, 2018
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    I just added a 4 pin push button , one pole is connected to the antenna and the other pole is connected to ground through a resistor . Amplitude is reduced significantly when I press the button but the oscillation's frequency remains stable
     
  8. danadak

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  9. jpanhalt

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    Jan 18, 2008
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  10. ExpL0siV3Man79

    Thread Starter Member

    Jun 4, 2018
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    So you say that I can't make a band pass filter out of crystal oscillators . For a 32.768kHz signal what is the length of the wire (antenna) in meters . The width of the wire is 22mm
     
  11. jpanhalt

    Expert

    Jan 18, 2008
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    Here are the designs. I followed the FEBO design and used 100 ft of shielded coax:
    http://www.stormwise.com/page28-VLF.htm
    Here's the antenna I made: https://www.febo.com/time-freq/wwvb/antenna/


    Here's my receiver schematic w/ antenna:
    upload_2018-8-9_7-18-15.png

    My antenna:
    upload_2018-8-9_7-24-10.png

    And the tuner/match box:
    upload_2018-8-9_7-25-22.png

    I was an air core variable capacitor to get close, then used mica fixed capacitors for the final tuning. Mine was tuned to 6o kHz (WWVB), but you can tune to any VLF.
     
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  12. ExpL0siV3Man79

    Thread Starter Member

    Jun 4, 2018
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    This is the transmiter circuit : http://tinyurl.com/y8wur7md
    analog out == antenna
    P.S. frequency is 32.768 kHz not 400Hz
    Can't I use just one wire (long or short I dont really care) to receive the signal ove a distance of around 10 - 15 meters ?
     
  13. jpanhalt

    Expert

    Jan 18, 2008
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    So far as I know, you can use a coat hanger. 32768 Hz is about 9155 meters in air; shorter in water based on the refractive index. Anything practical will be "short" in radio theory.

    Where did the "400 Hz" come from? Your original post mentioned 24 kHz, now 32 kHz. My experience is at 60 kHz, which is close enough for comparison. I have also listened to the Soviet/US? submarine bands on SDR at lower than 24 kHz as I recall.
     
  14. ExpL0siV3Man79

    Thread Starter Member

    Jun 4, 2018
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    I used this frequency for demonstration purposes . I increased the 555 timer oscillation square wave frequency at 53.something kHz . Now what is the length of the wire needed ? if I use it to transmit under sea water how shorter does the wire become??
     
  15. jpanhalt

    Expert

    Jan 18, 2008
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    Look up "refractive index." It is wavelength dependent. Since your antenna(s) will be a small fraction of the wavelength in any case, you decide how long a wire you want or can use and design around that. You have been given several links on point.

    Edit: Here's a link that might help: https://en.wikipedia.org/wiki/Wavelength
     
    Last edited: Aug 9, 2018
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