Two transmitters, one receiver speaker-microphone circuit

Discussion in 'Analog & Mixed-Signal Design' started by fp1996, Jan 13, 2017.

  1. fp1996

    Thread Starter New Member

    Jan 13, 2017
    I'm doing an analog electronics project now, and the aim is to use signals from two speakers, and receive both of them with one microphone.

    The signals that are given by the speakers are signals of different frequency ranges, and have different voltage offsets.
    I am interested in finding the difference between the DC offset value of these signals.

    However, as far as I've learned, if I receive both of them with an electret microphone and filtered them, its output removes all information about the DC offset value,
    so how could I be able to preserve those values? Is there some other way to do this? (Using antennas, infrared sensors or LEDS etc is also possible)

    NOTE: We HAVE to use two transmitters and one receiver.
  2. #12


    Nov 30, 2010
    There must be a misunderstanding. Speakers can not perform DC. That's called, "wind". It always goes the same direction and has a steady velocity.

    If you apply a DC current to the speaker you might be able to optically measure the displacement of the speaker cone from its rest position. How to measure both speakers with one sensor escapes me at the moment.
  3. Motanache


    Mar 2, 2015
    It seems to me a problem to check knowledge about filtering.

    Can not directly send a signal that has DC component through sound, infrared or radio waves.

    The solution, any of the options would you choose, be a higher frequency modulated with given signal or a chopping (two different methods):

    Take the example of two speakers and one microphone(the first method with modulation).
    Each speaker will have a different carriers frequency that it emits.

    Each of these two carrier frequencies will be modulated with one of two given signals.

    With microphone we get this signal that is a mixture between these two.
    After microphone then preamplifier follows with two filters to separate these two carriers frequency.

    After that follows demodulation and obtaining initial signal.

    If will be up to me I'd make an A / D conversion of signal and would send data either by sound or by radio or light. In digital data for each signal may be preceded by a proper ID to each signal.
    Obviously for transmission via sound signal given should vary more slowly.
    Since it is just $ 2 a microcontroller with A/D conversion.

    But I realize that the digital and analogic at school are different courses, must find a way only analog.
    If you work with two radio transmitter and single radio receiver, you must use the same frequency for all.
    The simplest is chopping with a different chopping frequency for the each signals.
    At the reception we have filters that separate these chopping frequencies.

    It depends on the modulation method.
    If is amplitude modulation (AM), the DC component is lost.
    If is frequency modulation (FM) , the DC component is lost.

    The microphone did not receive any continue component. It not measure constant air pressure. Only variations.
    Last edited: Jan 14, 2017
  4. crutschow


    Mar 14, 2008
    As #12 noted, speakers only output AC so there cannot be a (DC) voltage offset.