Switch for 2 way radio project

Discussion in 'The Projects Forum' started by robbo99, Aug 20, 2013.

  1. robbo99

    Thread Starter New Member

    Aug 20, 2013
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    Hi, all. I am by no means an electronics expert so please be gentle!

    I need a switch that sits in a circuit with two inputs (input 1= N/A, input 2 = 2 way radio) and a single speaker output.

    I want the radio input only to be triggered when a signal is received on the radio or when a user hits a button. So in effect input 1 is always on unless input 2 is triggered by a radio signal or physical depression of a button. Once the button is released or the radio signal stops, i want the switch to flick back to input 1.

    Any ideas on such a switch?

    I have had this suggested to me, but looking for an expert http://www.fairchildsemi.com/ds/FS/FSA5157.pdf

    thanks
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,151
    3,058
    The manual button operation is easy compared to the "automatic" switching based on a radio signal.

    Are you thinking this will allow you to listen to whatever you like until someone comes on the radio, at which time your tunes or whatever are replaced by the radio signal? What sort of 2-way radio is it?
     
  3. robbo99

    Thread Starter New Member

    Aug 20, 2013
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    hi, yes thats right signal 1 is audio which needs to be always on unless triggered off by an incoming radio signal.
    radios are just standard 2 way radios, nothing special.

    Got any suggestions on the switch?
    Thanks
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,151
    3,058
    What you need, I believe, is a form of squelch. If this function is not built into your radios already, then you need to make your own. I'm not the person to help with that.

    I think if you can get a squelch function working, that on/off signal can be used to switch the audio source as you need.

    That switch you linked appears to be meant for switching the power output of the audio system. I would prefer to switch at the level of the input signal, so there is one amp and one speaker, but two signal sources. Would that make sense on your arrangement?
     
  5. robbo99

    Thread Starter New Member

    Aug 20, 2013
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    Hi wayneh,

    thats right, switch at the input level so there is a clear break between the audio output of the ipod and the incoming signal from the radio i.e. 2 signal sources.

    Someone suggested using a relay as a switch to flip between inputs, the relay being triggered with a noise on the radio input. the guys in Maplin weren't so sure.

    any thoughts?
     
  6. inwo

    Well-Known Member

    Nov 7, 2013
    2,433
    315
    Last edited: Jun 5, 2014
  7. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,545
    1,252
    The Fairchild part has a max signal range of 5V p-p and a peak signal current of 500 mA. This was designed for a cell phone, and will not handle cleanly the signal of a normal 4 or 8 ohm speaker. I agree with inwo, there are a ton of VOX products and projects on the innergoogle to buy or build.

    ak
     
  8. robbo99

    Thread Starter New Member

    Aug 20, 2013
    5
    0
    thanks for your replies. i checked out the VOX switch; it looks to be right, kinda annoyed i didnt see this when i was already looking at a VOX to avoid having a PTT for transmit mode.

    anyway, i found this site (http://circuitsbook.com/voiceoperatedswitch.html) but im not clear on this...

    where am i supposed to plug the different circuits to? i.e. vos would trigger connection of the radio circuit, and break the ipod circuit.

    perhaps im being dumb
     
  9. inwo

    Well-Known Member

    Nov 7, 2013
    2,433
    315
    The relay contacts aren't shown in the schematic.

    Radio output to input of vox.
    Connect the speaker to common.
    Radio output to NO.
    Standby audio to NC.

    Or whatever audio levels used switching and sensing.
     
  10. robbo99

    Thread Starter New Member

    Aug 20, 2013
    5
    0
    blast from the past...just came across this thread in an old email...

    in case anyone's interested, this thread was just the start of my journey into the creation of a product i call the Airwave. you can find out more about here at www.theairwave.co.uk

    thanks
     
  11. ebeowulf17

    Active Member

    Aug 12, 2014
    678
    79
    Wow, that's come a long way in a year. Congrats!
     
  12. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    a simple way is that if the radio has a light that indicates the radio is reciving a signal, use that as an output to drive a relay. or look at the specs for the radio, most of my ham radios and he buisness band radios I am familiar with have a switched output comming out to an accessory jack already.
     
  13. Art

    Distinguished Member

    Sep 10, 2007
    785
    61
    It would be much nicer to look at the AGC (the signal LED) than voice, then you'd get the switch with the received carrier and music would clear when noise would clear on the radio .. And you'd have the same silence buffer that you'd get on the radio.
     
  14. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    agc voltage is not normally used for squelch, they use background noise or hiss, which is reduced when recieving a carrier. a high pass filter in the audio line picks off the noise which is rectified and filtered to give a changing voltage when a carrier is recieved,
     
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