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  • How to generate the sound of a certain frequency?

    Angello

    Member

    Updated: Oct 26, 2024
    Views: 1.2K
    Hello everyone!

    I'm and elec eng student. I'm on the first year of studies and I already have a project in Digital Systems.
    I really don't know where to start with the project.

    Basically project is:
    To design and construct a single octave digital piano/keyboard.

    As I said I have no idea where to start. I searched net with google, found some circuits and etc.

    I don't really get tho, why there are transistors, Schmitt's triggers in the circuits.

    Can anyone tell me how to get a certain frequency from the speaker?
    Why most of the circuits involve transistors and Schmitt's triggers?

    I don't want you guys telling me what exactly to do, but give me maybe some links for useful info. Explain why to use certain components etc.

    Thanks in advance guys.
    Regards
    Angello
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Replies

  • reachrkata

    Member • Oct 31, 2009

    I think this link gives a circuit to you without the need of Schmitt triggers -

    <a href="https://ece.uprm.edu/%7Epol/pdf/icee04CruzPol.pdf" target="_blank" rel="nofollow noopener noreferrer">PDF</a>

    - Karthik
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  • nucleuz

    Member • Oct 31, 2009

    Its not very difficult
    it actually very easy project.first try to make a so many square wave of different frequency with the help of micro controller.U can adjust the frequency by changing the delay time. Connect the port pins to speaker with the help of push buttons.if u generate 10 square waves u can hear 10 different sounds.

    Regards
    Jishnu
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  • Angello

    Member • Oct 31, 2009

    Thanks a lot lads for the help. I have to think a little bit more about what you said and posted me😉
    Can you also explain in simple english what Schmitt trigger does?

    Thanks
    Patryk
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  • nucleuz

    Member • Oct 31, 2009

    Schmitt trigger is a simple circuit.U r having a analogue signal.[​IMG]

    Here U is the Signal.And the red line show the threshold line.A is the Schmitt trigger output.
    working principle is very simple .when ever the input voltage cross the threshold voltage then the output will go to high.And when ever the voltage goes down to threshold voltage the out put will go to low.

    Regards
    Jishnu
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  • Angello

    Member • Oct 31, 2009

    So basically it changes the out put depending on its input? So in a way it behaves like a logic gate?

    The picture on <a href="https://en.wikipedia.org/wiki/File:Smitt_hysteresis_graph.svg" target="_blank" rel="nofollow noopener noreferrer">File:smitt Hysteresis Graph.svg</a>is confusing me tho. Why A behaves like a threshold and B like and High-Low out put?

    And#-Link-Snipped-# is also Schmitt Trigger right? Why is there Vdd Vss going in there? Or is it overall a Schmitt Trigger?

    Ohh and by the way, what Vcc Vss Vdd Vee stands for? Or is it and old way to descried positive and negative terminals of voltage? I keep reading different things on net about this V's with different subscripts, which makes me even more confused. And I'm only a first year!😛


    Thanks Jishnu for all the explaining.
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  • Angello

    Member • Nov 8, 2009

    Ok, so I got my frequency from 555timer, but it is a square wave and I need a sine wave.
    I was looking around the net for some schematics, but nothing specific really.

    I was thinking of using a bandpass filter - that what I found out could change square wave to sine wave, - but don't know how it should look like, what goes inside and what are values of either resistors, capacitors of inductors.

    Can anyone help me?
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  • joshce

    Member • Nov 25, 2009

    This may be late but hopefully helps someone:

    A schmitt trigger compares the input voltage to two thresholds. When the input crosses the lower threshold the output goes low, when the input crosses the upper threshold the output goes high. The purpose is noise immunity of the input signal. Your output wont go high-low-high if noise pushes it passed one threshold voltage but not both. A regular comparator would!

    The V subscripts have to do with transistors. You have two kinds: Field-Effect Transistors (MOSFET- work with metal on semiconductors and electric fields) and Bipolar Junction Transistors (BJT- two semiconductor junctions pn and np). If you look in a electronics index for either term you will see the diagram. Vdd is the drain voltage of a MOSFET. Vss is the source voltage of a MOSFET.
    Vee is the emitter voltage of a BJT. Vcc is the collector voltage of a BJT.

    Here is a hint for the music:
    Octaves are at integer multiple ranges of 110 Hz. You can change between notes by adding exponentials of 2 such as:

    220*2^(0/12) = 220 - bottom of the octave
    220*2^(1/12) = 233 - note2
    220*2^(2/12) = 247 - note3
    220*2^(11/12) = 415 - top of the octave
    440 is the next octave because 220*2^(12/12) = 440

    Generate different tones at those frequencies.
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  • Angello

    Member • Jan 8, 2010

    Joshce thanks a mil! At last I know what V's comes from😁
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  • Tsardoz

    Member • Jan 9, 2010

    Angello,

    Try looking for a "sine wave oscillator" on internet. There is plenty out there. In all circuits there will be a couple of components that determine frequency. You can use switches to switch different components in and out of the circuit.

    If you want to filter a square wave to get a sine wave, you could look at using switched capacitor filters.

    Or a microcontroller is a neat solution. Then the project becomes a software one rather than hardware. There are plenty of ways to skin a cat.
    eg.
    #-Link-Snipped-#
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  • Angello

    Member • Jan 10, 2010

    I got my freq with use of 555 timers. But another problem raised when I wanted to amplify these waves in an op amp to make them look more like ac current and also make it possible to hear them from speaker (and prevent burning the speaker with a dc).

    I use something like this :
    #-Link-Snipped-#
    Except with and output going to one speaker.

    The freq inferred with one another and and I got nothing(or maybe something like a white noise). Anyone can tell me why!?

    Another thing is described here:

    #-Link-Snipped-#

    please look at this and let me know for any possible solutions!

    regards
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  • Van Helsing

    Member • Jan 12, 2010

    Some time ago there was an IC by Mostek the MK50240. This awsome IC generated a full octave from a single input frequency. By now I really don't have any idea the master octave is generated. Anyway, if you are interested in the math that make "sense" on music take a look at:

    <a href="https://en.wikipedia.org/wiki/Music_and_mathematics" target="_blank" rel="nofollow noopener noreferrer">Music And Mathematics</a>

    This will explain why and how it works.
    Cheers.
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  • Saandeep Sreerambatla

    Member • Jan 12, 2010

    I guess you have to use a amplifier which amplifies the sound depending on the frequency you need.

    Use a amplifier which uses BJT ,such that you can design it according to the requirements like frequency , noise level etc..

    IF you use MOSFET then noise will be pretty much lower! but its costy.
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