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Some kind of morse code device

Discussion in 'General Electronics Discussion' started by Tomson, Nov 6, 2014.

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  1. Tomson


    Nov 6, 2014

    I try to build a morse code device but I have some problems.

    The concept is to use a momentary switch connected to a DC 9V battery and a device to generate a buzz as well as a mobile phone with headset.

    I thought of something like a piezo buzzer but I can't use a piezo buzzer because my plan is to generate a silent buzz signal wich shall be connected to the microphone pin of a mobile phone headset (3.5mm jack) and not be heard otherwise to transmit it over a call.

    So you could use two mobile phones each connected to such a modified headset to send morse codes (through a call) simply by pressing the momentary switch and hear incoming signals through the headphones.

    Has anyone an idea how a possible schematic could look and what components could be used?

    Thank you!

    Kindest Regards,

  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    Nov 28, 2011
    Hi Tomson and welcome to Electronics Point :)

    So you want to establish a call between two mobile phones, and transmit a "silent buzz" through the microphone that won't be heard by the people talking on the phones, but also will be heard? I think you need to explain yourself a bit better!

    Start by telling us WHAT you want to achieve, not necessarily HOW you think you can achieve it.
  3. Tomson


    Nov 6, 2014
    Hi Kris,

    Thank you for the fast answer. The mobile phones shall only be used to send the signal over a longer distance (as transmitters). Instead of speaking the mobile phones shall only send and receive the buzz tones through headsets. So that you could actually morse with no need to speak. So you press the button and the other person hears the buzz and can note it down for example. Then the other person can press their button and you will hear the buzz. I hope this explains it a little bit better. (It's quite hard, I am sorry)
  4. davenn

    davenn Moderator

    Sep 5, 2009
    I think he means it wouldnt be an audible buzz to the person doing the sending
    The is audio from the morse sender goes directly to the mic or preferably the external mic input socket

    That is do-able

  5. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    Nov 28, 2011
    OK, yes, you can modify a headset, or make a headset extension box with circuitry inside it and a socket for a normal headset or headphones or ear buds, so that the microphone audio comes from an oscillator that generates a frequency when a button is pressed. So if two people had the same thing, and they established a cellphone call between them, when one person pressed his button, the other person would hear a beep in his ears, and vice versa.

    You need a small battery-powered oscillator. There are lots of circuits available. It could be powered from a CR2032 lithium button cell, connected through the pushbutton so it doesn't consume any current when not in use.

    Would you like me to draw up a circuit design?

    Where are you located? (So I know which component supplier to recommend.)
  6. Tomson


    Nov 6, 2014

    davvenn got what I meant :)

    A circuit design would be very great Kris. This is a really generous offer from you. I hope I can return the favour somehow :) I am located in Germany and usually use or as suppliers for my projects but I am also able to order from any country within the European Union if needed. Thank you again for the support!

    Best Regards,

  7. Gryd3


    Jun 25, 2014
    This could be done with software as well...
    Otherwise you will need to connect your device physically with a headset plug, or wirelessly with bluetooth.
    Regardless of data transmission, you will need power for the device as well.

    Is using an iPhone or Android App out of the question? (I am not that fluent with programming for iOS or Android, so this is more of a theory. I cannot provide examples)
  8. galaxy


    Nov 3, 2012
    Maybe I am misunderstanding the requirements but every cell phone I have used will send dtmf tones.
    The longer you hold the key down, the longer the tone, so you can do 'dots and dashes'.
  9. shrtrnd


    Jan 15, 2010
    Wow, Morse Code coming full-circle. Audio transmissions killed-off Morse, and now somebody's figured-out a way to use audio to transmit Morse Code.
    davenn and KrisBlueNZ like this.
  10. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    Nov 28, 2011
    OK, just in case you still want an external circuit to do this, here's my design. It uses a Rohm BU4S584G2 single-gate CMOS inverter with Schmitt trigger input, a versatile device that can be used to make an oscillator with only one resistor and one capacitor and operates over a wide supply voltage range.

    It is an SMT (surface mount technology) component and these can be hard to prototype with, but it only has five leads and one of them isn't used, so you can actually mount it on stripboard fairly easily using two adjacent tracks with thin cuts through them. Or you can use a SSOP/LSOP breakout board.


    VR1 and C1 form a delay from U1's output back to its input and this causes it to oscillate at a frequency determined by this delay, producing a roughly triangular waveform at its input, with an amplitude of around 320 mV peak to peak.

    This triangular wave is smoothed by R1 and C2, to remove some of the harshness from the sound, and this signal is further attenuated by R2. An adjustable amount of the remaining signal is picked off by VR3 and fed to the microphone on the second "ring" (the one next to the grounded sleeve) of CN2, the plug that plugs into the phone.

    The left and right audio signals from the phone, on the tip and the first ring of CN2, connect straight through to the tip and ring of CN1, which is the socket for a standard set of headphones or ear buds. CN1 and CN2's ground connections are commoned.

    VR2 creates a 0V reference for the audio signal which is about half way between the positive and negative peaks of the waveform on U1 pin 2. Without this feature, there would be a big DC swing at the audio output each time the circuit was powered up.

    Because of the bias due to the DC path through R1, R2 and VR3, varying the setting of VR2 will skew the waveform towards a sawtooth wave of one polarity or the other, but if VR2 is adjusted too far from the centre, the oscillator will stop.

    Adjust VR2 for the desired tonal quality but not close to either of the points where the oscillator stops, otherwise it may not stop reliably.

    The three adjustments are independent except that adjusting VR2 (tone) will affect the frequency somewhat, and adjusting VR1 (frequency) will affect the usable adjustment range of VR2.

    Some links to components on

    U1: BU4S584G2:

    VR1: 100k trimpot:

    VR2, VR3: 10k trimpots:

    CD:100 nF ceramic:

    C1: 120 nF: (this one is actually 150 nF but that's fine)

    C2: 15 nF:

    R1, R2: 68 kΩ:

    Other parts:

    BT1: CR2032 3V lithium button cell in holder
    SW1: SPST momentary pushbutton or Morse key
    CN1 standard stereo jack socket
    CN2 special tip-ring-ring-sleeve jack plug to suit phone
    Stripboard or similar for prototyping
    Last edited: Nov 7, 2014
    davenn likes this.
  11. davenn

    davenn Moderator

    Sep 5, 2009

    I couldn't resist ;)

    new mobile phone  haha.jpg
    shrtrnd likes this.
  12. Tomson


    Nov 6, 2014
    Thank you for all the replies, especially Kris for the circuit design! I will try to built this device as it is for my little son who desperately wants to morse wit his friend. They only have old Nokia mobile phones and no smart phones so a software solution is not possible. I will be fun to build an test it. Nice picture davenn. This would probably be the perfect morse code device nowadays :D
  13. FuZZ1L0G1C


    Mar 25, 2014
    Re Forums>Electronics Forums>Circuit Help>Some kind of morse code device (@Tomson).
    Although this thread is already close on 3 years old, I'd like to add my penny's worth to this interesting topic:
    For a pre-recorded morse-message, you could use software with your sound-card to create a modulated tone.
    The continuous sine-wave of "#Hz" audio frequency is modulated by a PWM square-wave, the marks and spaces being defined by author, then mixed, duplicated, one ch inverted, shifted 1/2 cycle, reduced -5 dB then remixed.
    This creates a mono track of (eg) 300 Hz sine for MARK and silence for SPACE.
    Disadvantage: For long messages, this is very time-consuming to do.
    A quicker easier alternative is to use a digital-electronics simulator (German software company), which allows you to build, run, and compile any number of logic designs to run (virtually) on your computer.
    By combining a virtual tone-generator with ADC, driven by a text-file input, logic gates, drivers and data-busses, a 'morse-code-generator' can be built on computer.
    I would mention the software name, but not sure if this would be flagged as 'spamming'.
    1010100111011101110010101 is the binary sequence for SOS.
    Hope this helps ;) Clive
    PS- output can be recorded to MP3 and/or saved as .WAV or .RAW data.
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