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Tone Generator Connected To Speaker

  1. Aug 28, 2010 #1
    First, let me just say that I am very new to electrical engineering. It is something that I started teaching myself mere months ago. So, basically, it is probably best that you guys assume I know nothing.

    As I have expanded my knowledge, I have built some little things. For instance, an LED light, an electro-static (Van de Graaff) generator, a "brushless" DC motor, et cetera...

    Most recently, I have been trying to make a little tone-generating circuit. I originally thought I could just connect an LC circuit to a speaker, and run a current through it. Upon researching why that did not work, I came across Hartley and Colpitts circuits, both of which used a transistor to keep the oscillations going.

    So, I got a transistor. Still, no tone. I have tried numerous simple circuits that I have seen online. Any tones should have been within the audible range. Yet, I have heard none.

    Thinking I might need to amplify the signal, I have tried connecting some of my circuits to the Line In on my computer, rather than directly to a speaker. Typically when connecting to Line In, I would get my power directly from one of my computer's 5V connectors. Such seemed easier than using a battery.

    Basically, I was wondering if you guys could show me a circuit that should work. Maybe then I can figure out what I am doing wrong...

    I currently have two capacitors of 10 µF each and one that is 470 µF. My three inductors are each 100 µH. I also have an MPS2222A transistor and a plethora of 1/4 W resistors.

    I appreciate any help you guys can give me! Thanks!
  2. jcsd
  3. Aug 28, 2010 #2


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    I have a small circuit which makes a surprising level of noise in a speaker.

    It needs an NPN and a PNP transistor and this means you have to be careful about which leads go where.

    [PLAIN]http://dl.dropbox.com/u/4222062/NPN%20PNP%20OSC.PNG [Broken]

    This has the waveform shown, so it sounds a bit rough, but it will certainly make some noise. It runs off a 1.5 volt battery and is OK for such things as a door buzzer.
    The speaker is shown as an 8 ohm resistor in the circuit.
    As it stands, it would oscillate at about 140 Hz, but this could be changed by varying the 100 K and the 0.1 uF capacitor.

    It is possible that your oscillator was not oscillating. An LC oscillator has to have components whose reactances were carefully selected.
    Last edited by a moderator: May 4, 2017
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