Build an audio switch with channel priorities

Discussion in 'Radio Propagation Questions' started by Jessieight, Jan 4, 2018.

  1. Jessieight

    Jessieight New Member

    I am building an audio switch with channel priorities.

    I will use this in car events where we communicate car-to-car on FRS radios. A few of us also use 2 meter amateur radios for longer range communication. The intent will be that, when no radio signal is being picked up by either radio, the audio from my media player will be on. If a signal is detected on the 2 meter radio, the switch will mute the media channel and play the 2 meter audio. If a signal is detected on the FRS channel, no matter what other signals are present, it will be selected.

    I have found a signal detection ship I intend to use as part of the circuit: (NJM2072D - )


    The above image is extracted from the datasheet for reference.

    • There appears to be a capacitor symbol above the "INPUT" label connected to pin 1 but there is no associated value. I find no indication in the datasheet about how to select a value. Is this just a DC blocking cap? What would be an appropriate value?
    • Pin 2 is labeled "GAIN" but there is no description of what component to attach to vary gain. Does the internal schematic suggest anything?
    • Pin 5 shows what appears to be a 10uF capacitor but the schematic symbol is confusing. This cap is used to adjust recovery time. Does the symbol indicate I should attach this pin to ground if no cap is used?
    • The example enter code here application circuit shows the audio signal being sampled after an microphone amp. My intention is to sample the audio at speaker output signal levels. Does this appear to be a problem and, if so, what signal conditioning would I have to apply?
  2. G4ZFQ

    G4ZFQ New Member

  3. jerry51

    jerry51 New Member

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