How do I interface audio amp to key encoder

Discussion in 'The Projects Forum' started by Etronic, Dec 15, 2014.

  1. Etronic

    Thread Starter Active Member

    Oct 7, 2011
    127
    2
    Hi all



    I need to know has anyone on here ever used a keypad encoder like the 74c922 from Digikey.



    I need to interface an Audio amps output to the encoder IC. So I could pick up keypresses from another

    keypad that I already build.It has an audio feedback sound when each key is press.trying to mimic the keypad

    by using the Audio amp to pickup the sound from each key that is pressed with the second keypad setup

    using an audio amp interface to the 74c922 encoder IC.



    Does anyone or some one on this site know or what I could use to interface between the audio amps output and the 74c922 encoder.There must be a why to do this.

    mimicking a keypad. I hope you understand me and what I'm doing. School research project.





    All help is appreciated.
     
  2. lightingman

    Senior Member

    Apr 19, 2007
    374
    22
    The 74C922 is a 4X4 keypad encoder in its own right. I scans the keypad and gives a binary output dependent on the key pressed. It also gives a valid key-down output. I feel that this maybe the wrong device for what you are doing.

    Could you give a little more info?

    Daniel.
     
  3. Etronic

    Thread Starter Active Member

    Oct 7, 2011
    127
    2

    No? Its the right encoder chip i need. I need what I stated in the post. I need to interface an audio amps output to the encoder chip I stated.
    I'm looking for one chip or 2 chips that will interface the audio amp output then some other chip to connect to the encoder like mimicking a key pad But. With out using a keypad. The audio amp replaces the keypad. NOT DTMF. As you are thinging. assuming.

    Any body else can help.
     
  4. lightingman

    Senior Member

    Apr 19, 2007
    374
    22
    So let's get this right....

    The 74C922 has four X lines and four Y lines. There are four outputs that scan the keypad and four that receive an output from the key that has been pressed. The decoder in the IC selects the valid key by sending an output to each row of switches, one at a time. If let's say switch 2 on the second row is pressed, the first row will be enabled and the decoder will sense no signal (no switches pressed on that row) it will now switch the first row off and the second row on. At that point, the decoder will sense that the second switch on that row is pressed and the appropriate output will be given. At the end of a complete scan of the keypad, it will all start again.

    What I am saying is that you will need physical switches or CMOS switches such as the CD4066 to mimic them. Using four CD4066's will give you 16 switches and therefore, 16 separate inputs. You can then interface them to other devices.

    Having said that, all you have really achieved here is a 16 line to 4 line decoder and something like a CD4067 would do that without all the work.

    Daniel.
     
  5. Etronic

    Thread Starter Active Member

    Oct 7, 2011
    127
    2
    lightingman

    You are Correct on your statement above?

    Right replacing physical switches or keypad. using the chip you suggested.

    So this CD4067 will mimic a matrix switch keypad. Is that correct.

    How do I connect my audio amps output to the CD4067 or do I need some other chip to interface to the audio amp, before the CD4067. AND what pins on the CD4067 get connected to the row pins and the column pins on the 74c922 encoder. need more help Please.
     
    Last edited: Dec 16, 2014
  6. Papabravo

    Expert

    Feb 24, 2006
    10,179
    1,800
    As I understand what you are saying, you want to connect the output of an audio amplifier to a decoder. I don't think that is possible in any meaningful way. Don't you want the output of the audio amplifier to be connected to a speaker. There is a "Data Available" signal from the decoder you can use to enable the amplifier to make a sound. Is that what you want to do.

    I'm surprised you can still get this part since it was from the much deprecated 74C series of logic chips.
     
  7. lightingman

    Senior Member

    Apr 19, 2007
    374
    22
    I am sorry and not being rude my friend, but this is not making sense now.

    The output of your amplifier (if say 100 watts) could be around 28 volts. Put that into any digital IC 74, 74HC, 74C or 4000 series will destroy it instantly.

    I would really like to help, but I am now a little confused at what you are trying to achieve.

    What I was trying to explain is that if you were to connect 16 CMOS switches to the crosspoint I/O's of the 74C922 and then read them as a four bit binary result, you would simply have a 16 decimal input to four bit binary decoder. The 4067 is just that.

    Daniel.
     
  8. Etronic

    Thread Starter Active Member

    Oct 7, 2011
    127
    2
    Tell me this? Does the CD4067 mimic a 16 switches of a 3X4 and 4X4 matrix keypad (Yes or NO.) You stated in post #4 that it will.

    This is the kind of chip I need? To replace the keypad. but? mimic the same functions as the keypad. Does the CD4067 DO THIS.

    My audio amp output is nowhere close to (100 watts) Its more like 800 mW or less. At 5V power supply.
     
    Last edited: Dec 16, 2014
  9. Etronic

    Thread Starter Active Member

    Oct 7, 2011
    127
    2
    lightman
    What I was trying to explain is that if you were to connect 16 CMOS switches to the crosspoint I/O's of the 74C922 and then read them as a four bit binary result, you would simply have a 16 decimal input to four bit binary decoder. The 4067 is just that.



    Tell me this? Can the CD4067 mimic 16 switches in a 3X4 and 4X4 matrix keypad (Yes or NO.) You stated in post #4 that it will.



    This is the kind of chip I need? To replace the keypad. but? mimic the same functions as a matrix keypad. Does the CD4067 DO THIS.

    My audio amp output is nowhere close to (100 watts) Its more like 800 mW or less. At 5V power supply.
     
  10. JWHassler

    Member

    Sep 25, 2013
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  11. Etronic

    Thread Starter Active Member

    Oct 7, 2011
    127
    2
    Please can some one tell me how to do this.


    Could you tell me How do I connect the 74c922 outputs to the input of pin2 on the 8870 DTMF decoder. there only one input on the 8870 pin two to detect the tones. Do I need another chip between
    the 74c922 and the 8870.If so which chip and can you give me the pin out connections.Please Help!
     
  12. Papabravo

    Expert

    Feb 24, 2006
    10,179
    1,800
    You cannot connect digital outputs to analog inputs. No matter how big a hammer you have you cannot pound a round peg into a square hole. You might want to take a step back and describe what it is you are trying to do. The introduction of the 8870 is a new wrinkle.
     
  13. rogs

    Active Member

    Aug 28, 2009
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  14. JWHassler

    Member

    Sep 25, 2013
    201
    33
  15. Papabravo

    Expert

    Feb 24, 2006
    10,179
    1,800
    Holy autopilot batman! Have we been trolled again??!!
     
  16. Etronic

    Thread Starter Active Member

    Oct 7, 2011
    127
    2
    That thread you have mentioned has been completed by me over ten months ago. Without required help from any one else who posted there. And working 100% the way I need it to work.
    I had to work on it until I got it working without further help. And no one on that thread new how to solve the problem.
    But I did. Go figured that? And I'm not even an engineer. I'm only fourteen.
     
  17. Etronic

    Thread Starter Active Member

    Oct 7, 2011
    127
    2
    You don't know what you are talking about.That's why you have know positive answer or can give a positive comment. Batman!
    You can help or don't comment. Matter of fact I don't need your help.
     
  18. Etronic

    Thread Starter Active Member

    Oct 7, 2011
    127
    2
    No there's no trolling here.little man. just negative people like you who just waste other posters time. Batman! Grow help.
     
  19. Etronic

    Thread Starter Active Member

    Oct 7, 2011
    127
    2
    Hey Mr the one who baffled is you.Mr engineer.where;s you positive help on this post.Just negative comments.Don't help me or anyone else on here.
     
  20. Etronic

    Thread Starter Active Member

    Oct 7, 2011
    127
    2
    If you read the whole thread you might understand
    what I'm try to do. I know you can't connect diigital outputs to analog inputs. That why i mentioned what chip could I interface to the output of the 74c922 to the input of the 8870. maybe an DAC CHIP maybe not.what would you have mentioned if you read and understood my post.
     
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