Radio Transmitter , Range 15 - 20 meters , underwater wireless communication , Help with schematic

Discussion in 'Wireless & RF Design' started by ExpL0siV3Man79, Aug 9, 2018.

  1. ExpL0siV3Man79

    Thread Starter Member

    Jun 4, 2018
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    I am making a radio transmitter for underwater communication . The project will run on sea water and the device should run using a 32.768 kHz crystal ... I thought of using a Pierce (inductor-LESS) oscillator which looks likes this (photo) . The NOT gate used is a 74HC04 ,{ I also have a schmitt trigger inverter model : 74LS14 in case I need it . } . the capacitors are 18pF value Rf value = 1 MOhm R2 = 220Ohm ( I dont know if it's the right choice though ) .... The thing is that I dont know if it works as an oscillator... Can anyone test it for me with an oscilloscope ? Or send me a schematic made for LTspice ? Any general advices ? Many Thanks ! :)
     
  2. Janis59

    Active Member

    Aug 21, 2017
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    I have digged this fishhole shortly thus I know its a rather big science. How You get it through if even have no Oscilloscope. You will need a mountain of apparatusses to solve this problem.
    First, the saltwater makes short for waves. At 2,4 GHz the decrease factor is ca 1000 000 000 fold through the some 10 cm thick layer. On the 27 MHz it is much lighter, about 1000 000 fold and at 1km long waves about 1000. Thus, the Long waves may seem the solution, but the size of antenna then is clearly impractical.
    Second, antenna must be well insulated from even a microscopic leak, and well, the all antenna calculation formulas are undefined because of water epsilon is roughly 81 instead of 1. Thus antenna must be computer modelled at sth like Ansys/Maxwell or etc, and later explored on the topics of SWR, Z(o), resonance, etc.
    Third, all that sh** is heavily dependant on the deapth, temperature, salinity and so on. How to adjust, unknown.

    So, its not impossible task but very much science-involving and only for small immersion deapths. However, this is message of joy probably, militarists partially have solved this for their shallow water submarines. How - have no knowledge. But for deep sea nuclear command centers it is still unsolved, seems.
     
  3. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Are you aware of the difficulties involved with radio communications through water? See, for example, this article . Could you use ultrasonic communication instead?
     
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  4. ExpL0siV3Man79

    Thread Starter Member

    Jun 4, 2018
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    Okay so I made a 555 astable oscillator circuit which runs on 53.(something) kHz and connected a speaker to it . This should theoretucaly emmit supersonic waves ? How can I detect those waves to make a receiver ?
     
  5. cariban

    New Member

    Aug 14, 2018
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    The attenuation of EM wave in salt water is significant higher than that in the area. It only works:
    1. The frequency is very low. Lower frequency has lower attenuation;
    2. The distance is very short.

    I agree with the point of Alec_t, ultrasound is a better solution for communication in the sea water.
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Theoretically yes; in practice, probably no. A normal speaker has a frequency response which tails off dramatically above the normal audio range; furthermore it is not waterproof nor is it acoustically matched for driving a water load. You would need a transducer similar to those used in fish-finders. That type is commonly driven at its self-resonant frequency, so a 555 might not be the best oscillator to use.
     
  7. cariban

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    Aug 14, 2018
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  8. ExpL0siV3Man79

    Thread Starter Member

    Jun 4, 2018
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    Can I use this if modified appropriately?
     
  9. Alec_t

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    Sep 17, 2013
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    You could try; but it's a low power piezo, so I doubt the range would be enough. What modification do you propose (apart from waterproofing it)?
     
  10. ExpL0siV3Man79

    Thread Starter Member

    Jun 4, 2018
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    maybe finding a way to amplify the emmited signal . extra OpApm , a diy enclosure or both
     
  11. cariban

    New Member

    Aug 14, 2018
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    What is bandwidth of your signal? If it is narrow band, any opamp could do the job. 20 meter is very short for ultrasound, so you don't need very high power.
     
  12. ExpL0siV3Man79

    Thread Starter Member

    Jun 4, 2018
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    Well I ve never done something similar so I didn't exactly understand you . There 555 chip is tuned at 53.something kHz the output of the 555 timer chip is then connected to a capacitor with an 1 Meg Ohm resistor to ground to get the negative 3.3 volts . The output of the capacitor is then connected to the non inverting input of the op Amp . Output of the op Amp is connected to piezo electric crystal's anode . Crystal' s cathode connected to ground
     
  13. ExpL0siV3Man79

    Thread Starter Member

    Jun 4, 2018
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    how can I add a 4 bit signal ?
     
  14. cariban

    New Member

    Aug 14, 2018
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    Just have a look at your title, it seems that you want to transmit radio, not data? If it is radio signal, is it FM, AM or other digital radio (for example DAB). You need wider bandwidth for FM radio than AM radio. In general, radio signal is considered as "narrow band".
     
  15. ExpL0siV3Man79

    Thread Starter Member

    Jun 4, 2018
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    if I had to go with radio the transmission would be AM but now you told me about ultrasonic and I don't know how this thing works at all
     
  16. cariban

    New Member

    Aug 14, 2018
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    There is no difference between ultrasonic or EM wave before the last emission stage. You just use a transducer to convert the electrical signal to ultrasonic wave. The receiver side the transducer convert the ultrasonic wave back to electrical signal.

    For AM radio transmitter, there are many kits you can buy from internet, just select the one meeting your requirement. Or as your initial idea of using 555 timer. Here I just found one guy has done this:
    http://electronics-diy.com/am-radio-transmitter-using-555-chip.php
     
  17. ExpL0siV3Man79

    Thread Starter Member

    Jun 4, 2018
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    Yeah I ve seen his design too and managed to make a prototype . My problem is with receiving the signal (AM or Ultra Sonic) . How can I receive the signal ? Won't other sound frequencies interfere with the transducer and create too much noise under water ? How can I make a tuned receiver
    . Please answer both for AM and ultra sonic . Many Thanks
     
  18. cariban

    New Member

    Aug 14, 2018
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    The noise is not a problem. The background noise is usually white, you just need to bandpass filter to filter out most noise, like those legend AM radio receivers. You may just buy the receiver kit as well. Then add the sound-electrical converter to the kit.
    Is your project just a hobby? If it is for serious usage, you need more professional design for both transmitter and receiver.
     
  19. ExpL0siV3Man79

    Thread Starter Member

    Jun 4, 2018
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    Yep the project is just a hobby . Band pass filter ? Don't I need an LC tank for that or a crystal? Can I make one using a 555 timer ?
     
  20. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    I suggest you read up about band-pass filters. There are various ways of implementing them.
    To transmit data, you could send it as coded pulses of ultrasound, e.g. as Morse code. Of course, you would have to find a way of decoding the message at the receiving end. An Arduino or other MCU could do that if suitably programmed.
     
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