Ttl ic frequency mixer not working.

Discussion in 'The Projects Forum' started by eswara1997, Dec 14, 2013.

  1. eswara1997

    Thread Starter Member

    Dec 14, 2013
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    I am trying to build a mixer to connect two oscillators to. I am using a ttl 74LS266 IC. However when i complete all of the connections i receive no output. THe frequencies are going in properly, but i receive no output. I also checked the other gates and saw that there was no output in any of them. I should be getting a high output on the other unused gates, however i don't. I tried 2 chips of the same model, and got no output from either one.

    can this be a malfunction of the chip itself. Is there anyway i can test this. Additionally what type of chip can i replace this with.

    Attached is the schematic of my circuit. The schematic uses a CMOS 4077 however i am using the ttl 74LS266. My two oscillators use 74LS132 chips instead of 4093s.

    I need a mixer and i am stumped by this dillemma.
    thank you!
     
  2. ronv

    AAC Fanatic!

    Nov 12, 2008
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    I could be wrong, and I probably am.:rolleyes: I think they are using the digital chip as a very high gain op amp. I think you need to use the cmos ICs and they probably won't be to stable either.
     
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    You are powering the TTL with 5V?

    The oscillators are not intended or designed to work with TTL gates. The TTL "mixer" in lieu of CMOs should work.
     
  4. eswara1997

    Thread Starter Member

    Dec 14, 2013
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    well my problem with the CMOS was that my CMOS started getting very hot so i trashed them. My oscillators themselves work fine. I'm getting frequencies. I did change up my resistors and capacitors to compensate for additional current. And yes i'm using 5 volts.

    Another person mentioned that this chip is an open collector and needs a pullout. Can someone elucidate?
     
  5. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Which chip?
     
  6. eswara1997

    Thread Starter Member

    Dec 14, 2013
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    the 266 is an open collector
    my lOL is max of 8mA, so my pull-up resistor will be 5/.008 which is 625 ohms for minimum value
    So what multiple of this do i use for my value.
     
  7. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Somewhere between 1K and 4.7K
     
  8. vk6zgo

    Active Member

    Jul 21, 2012
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    What are you trying to achieve?

    Using the rough formula f=1/1.2CR,with the pot set at its max,you will have an output frequency from that oscillator of around 416.67kHz,& from the other oscillator,around 555.56kHz,giving a difference frequency of around 138.89kHz.
    You should be able to adjust the pot to reduce the difference frequency into the audio range,& ultimately to "zero-beat",where there will be no output from the "mixer".

    It could be that you have already inadvertently reached zero-beat,so it may be an idea to adjust the pot.
    Alternately,the LP filter consisting of the 1nF cap & 10kΩ resistor may be rolling off a very high difference frequency----have you checked for output directly on the I.C. pin?

    You can check the "mixer" I.C. by connecting one input to +5V & looking to see if the other input signal appears at the output.
     
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