Mixer circuit with input priority ?

Discussion in 'The Projects Forum' started by mbabayan, Jul 12, 2010.

  1. mbabayan

    Thread Starter Member

    Jul 12, 2010
    30
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    Hi,

    I'm thinking about building a motorcycle intercom system, and the core of it would be a mixer circuit. Now, I found plenty of those online, but they all miss a feature that I need:

    I need for different inputs to have different priority, so when signal appears on an input, all inputs with lower priority get faded automatically. When signal disappears, level should return back.

    I'm not sure where to start looking - any direction would be greatly appreciated.

    Thanks
    -MB
     
  2. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    That can be done with some simple combinational logic and a few analog switches, such as 4016's.

    Am I correct in assuming you want a "first come, first served" priority?

    You might also look at some of the audio control consoles described in recent editions of the ARRL Handbook. Hams have been doing this sort of thing for a long time. :)

    Eric
     
  3. Dx3

    Member

    Jun 19, 2010
    87
    7
    I am reminded of grocery store announcment circuits. When the manager picks up the microphone, it stops the muzak and allows the voice to be amplified. I can't remember where I saw that circuit.
     
  4. mbabayan

    Thread Starter Member

    Jul 12, 2010
    30
    1
    If first come first served means time based (what input signal appeared first), then no.
    Priority should be input based, in that, it is fixed. Some flexibility would be nice too, e.g., in order of decreasing priority (sources don't matter, just to name them)
    - Intercom has top priority
    - Two-way radio
    - GPS
    - Music

    when signal appears on, say, two way radio, GPS and Music get faded, but intercom still has priority.
    I would actually prefer for fade, not complete cutoff. Possibly gradual fade-in back when overriding signal is gone.
    Basically, each input would trigger a "gate" that would decrease level on the below inputs and gradually rise it back when untriggered.

    Now, I feel terribly out of context here - what is ARRL handbook? I found it online though.
     
  5. windoze killa

    AAC Fanatic!

    Feb 23, 2006
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    I know exactly what you are trying to do.

    Firstly you need ccts to detect the audio I/P levels. These detected levels can be used in a logic switch arrangement. These can then be used to switch the outputs of a 4016 as KL7AJ suggested.

    Can you tell us how many inputs and what order of priority you want?
     
  6. mbabayan

    Thread Starter Member

    Jul 12, 2010
    30
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    Just attached a very high level and overly naive diagram :)
    This doesn't take into consideration the fact that at least some inputs and both outputs are stereo.


    Ok, the stretch goal :) :

    4 line level inputs with 1-2-3-4 priorities get mixed in (in according to priority). Signal above threshold (adjustable) fades out anything with lower priority.
    On top of that, 2 mic inputs which are mixed in _after_ main mixing has happened. There should be two separate outputs, which both get main mixed in signal as well as _one_ mic.
    Noise cancellation comes in the picture somewhere as well :)

    Now, with 4016, I wouldn't be able to gradually fade-in the volume back, would I?
    What does CCTS stand for?

    Thanks.
     
    Last edited: Jul 12, 2010
  7. windoze killa

    AAC Fanatic!

    Feb 23, 2006
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    Firstly "cct" is an abreviation of circuit.

    Jumping to the end first. I assume the mic I/Ps are for the intercom. If so do you expect these to be voice activated (background noise could be a problem in helmet)? If not if you press a switch to activate the mic then your priority for these disappears. The switch can mute the other I/Ps at the same time. You would want a gradual fade in after a few seconds to allow the other person on the bike to reply before it starts coming back on.

    As far as the other I/Ps this still wouldn't be too much of a probem. The 4016 is just a switch. You would need other audio circuitry to handle the fade in and fade out parts. Simple timing ccts should be able to do this. In conjunction with the I/P selector cct switching the 4016.

    I am not sure what 4 inputs you would want on a bike. Radio is one and phone another but what else would you need?
     
  8. mbabayan

    Thread Starter Member

    Jul 12, 2010
    30
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    Just attached a high level diagram of what I want to do to my previous reply.

    Audio should be full-duplex between the two mics, phone-like conversation.
    Noise reduction and/or VOX will have to be dealt with.

    4 inputs I'm thinking about are two-way radio, GPS navigation, music and phone.

    Does what I drew make any sense from high-level block prospective?

    Thanks.
     
  9. windoze killa

    AAC Fanatic!

    Feb 23, 2006
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    I will try and get you some sort of cct on here by the end of today. Currently I am missing a heap of libraries.

    In the mean time I don't think you need a mixer. Just a switch to select the required I/P.
     
  10. mbabayan

    Thread Starter Member

    Jul 12, 2010
    30
    1
    Thanks a lot !

    I think I'd need a mixer if I'm trying to fade-out the lower priority inputs instead of cutting them off.

    For just simple switching, I had an idea of switching using 8 channel demultiplexer (which would, naturally, have 3 control lines), feeding signal trigger from 3 top out of 4 inputs to them. This, and proper wiring of the 4 inputs to the multiplexer inputs would do the switching just fine - like this:

    Input 1 -> C1
    Input 2 -> C2
    Input 3 -> C3

    This would give me 8 combinations of signal presence.

    Wiring demux inputs corresponging to:
    001, 011, 101, 111 to Input 1,
    010 and 110 to Input 2,
    100 to Input 3 and
    000 to Input 4

    gives me the desired priority switch.

    Is this insane?:)

    Your circuit is still hightly appreaciated !:)
     
  11. windoze killa

    AAC Fanatic!

    Feb 23, 2006
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    Firstly I haven't been able to do the cct today. The IT people haven't fixed it yet.

    Secondly you don't want a multiplexer. Most of these are only digital and will be no good for audio. Also you don't want to mix the signals as you will get a really weird sound. What you need to do is switch the required input to an amplifer. You can do the fade in fade out bit at the amplifier. The fade out needs to be controlled but depending on the speed of the fade out and the following fade in you may lose a lot information.

    For example, if the GPS is trying to tell you to turn the advice will be over by the time the music fades out and the GPS fades in. This can be a problem even with a short fade out fade in setting.

    I think the main thing you should consider is making sure each of the I/Ps have a similar volume. That way when it switches from one to another it doesn't blow your ears out.

    I will have a think about what might be the best way to do it.
     
  12. mbabayan

    Thread Starter Member

    Jul 12, 2010
    30
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    I've been thinking about this one: http://www.nxp.com/#/pip/pip=[pip=74HC_HCT4051]|pp=[t=pip,i=74HC_HCT4051] - it appears to be able to switch analog signal, isn't it?

    I agree that I'd have to correct the level of I/Ps before switching, but since I wanted individual volume control on inputs, that's a given anyway.

    As far as fade, I don't really want fade-in/out. Ideally, I want to instantly drop level on lower channel when higher priority signal appears, and when it's gone, fade that channel back in in couple of seconds.
     
  13. windoze killa

    AAC Fanatic!

    Feb 23, 2006
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    That chips does seem to be able to do signals upto to about 170Mhz. Good choice.

    I will see what I can do regards the rest of it.
     
  14. mbabayan

    Thread Starter Member

    Jul 12, 2010
    30
    1
    So, I've spent quite a few hours in the LTSpice and I think I have the preamp and signal level detection part more or less figured out.
    I have output triggering from low to high when the input is above threshold.
    The issue is that it has no "inertia".

    What I'd like to add there is a delay circuit - when signal presence is detected, trigger-on in instant, but trigger off is delayed by, say, 2 seconds. Each occurence of detection of the signal resets the delay, so, it would take 2 seconds of "silence" to trigger off.

    I've been searching all over the internet including allaboutcircuits for 555 based circuits, but everything that I find do not implement what I need - they all implement predefined duration output pulse.
    Could you point me in right direction?

    Thanks,
    -MB
     
  15. windoze killa

    AAC Fanatic!

    Feb 23, 2006
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    Sounds like all is going well. Well done. I am sorry I haven't gotten back with any designs but I haven't had time at work to even scratch.

    In regards to you timing problem it should be very easy to do with 555 timers. You may need to use more level detectors in an opposite manor. To trigger the timer when no signal is present so I guess it would be a no signal detector. When the signal level drops then the output would trigger the timer.
     
  16. mbabayan

    Thread Starter Member

    Jul 12, 2010
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    One issue that I have is that there appears to be no 555 chip in LTSpice - I know that custom components could be defined there - where do I get 555 definition though?
     
    Last edited: Jul 16, 2010
  17. windoze killa

    AAC Fanatic!

    Feb 23, 2006
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    I find that quite strange. Probably the most used chip of all time. I have never used LTSpice so I don't know why it wouldn't be there.

    Are you looking for different varieties? NE555 LM555 you could try the dual timer 556.

    Try looking through this site http://home.cogeco.ca/~rpaisley4/LM555.html

    Very usefull.
     
  18. mbabayan

    Thread Starter Member

    Jul 12, 2010
    30
    1
    So, this is what I have come up so far.
    Does it make any sense outside of the simulator ? :)
    ( I did find 555 model in LTSpice, eventually).

    I can't find models for 4016 though, and, obviously, that multiplexer is not there.

    I went through the datasheet for the mux and it seems like to be able to switch audio, I need a negative reference voltage - how do I get something like -3.3 out of +9V ?
    I've tried inverting opamp, but all I get it +1V for some reason, I'm really confused on this one.
     
  19. mbabayan

    Thread Starter Member

    Jul 12, 2010
    30
    1
    bump :)

    I would really appreciate a sanity check on the cct as well as an advice about negative voltage.
     
  20. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    The circuit will have trouble with the biasing.
    Take a look at figure 3 in the attached PDF.
    It contains a lot of tips on using opamps on a single powersupply.

    Bertus
     
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