Problem with BCD to decimal decoder (K155ID1)

Discussion in 'The Projects Forum' started by zOlt, Feb 16, 2009.

  1. zOlt

    Thread Starter New Member

    Feb 16, 2009
    3
    0
    Hello,

    Noob question.. :rolleyes:

    I have a problem here trying to test a few K155ID1's that I've came across but i just don't get how they work.

    Ive tried using this simple schematics to test it out but no luck. Can someone tell me what I'm doing wrong.

    So when you look at the truth table if all 4 inputs are low (0v?) output "0" shoud be on turning IN-14 bulb on right? I mean the gate should open letting the common ground to pass the IC and turn on the lamp. Or im totally off here :confused:

    even when i try different combinations relaying 5v to inputs accordingly it just doesnt work.

    Here's the scematics im trying to do.
     
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  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    If you get the data sheet for a 7441 IC, you will see that all outputs are disabled for any input above 9d. Your drawing has all inputs floating, so there's no telling what might go on.

    To test this IC, pull the inputs up to +5 through individual 4.7K resistors. Then you can apply ground to the inputs in such a way to make up the BCD for 0 - 9.

    If you don't have a Nixie tube handy, just use a 10K resistor to pull each individual output up to some DC voltage and check to see if the correct one goes low for the BCD input.
     
  3. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    Two problems I have noticed.

    a. There is no anode current limiting resistor. Check that they are required or not.

    b. TTL inputs defaults to HIGH logic level if left unconnected. Your circuit does not indicate connections to 0V on the inputs. If you left them open, then there will be four HIGHs and according to the truth table, there will be no output for 74141.

    First test the operation of the display by jumper the corresponding pin to 0V to confirm the digit glows. Then you can test the operation of the 74141.
     
  4. zOlt

    Thread Starter New Member

    Feb 16, 2009
    3
    0
    Tube is not the problem because it works just fine when i skip the IC.

    So you are saying that for instance if i want to enable output "5", i need to connect 5V to inputs C and A and connect ground to inputs B and D, because i tried that and it makes no sense :confused:

    All i need to know what to connect to inputs to get LOW

    Truth table
     
  5. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    When a bit on an input is 0 connect it to ground.

    When a bit on an input is 1 connect it to 5V.

    According to your diagram, for the lamp to turn on you need to connect all inputs to ground.
     
  6. zOlt

    Thread Starter New Member

    Feb 16, 2009
    3
    0

    BEST ANSWER!!! Thanks mate :)

    ///CLOSE THREAD
     
  7. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    You are welcome ;)

    That is why we are here.
     
  8. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    Just to clarify if someone later found this thread.

    The 7441 do "react" to BCD code higher than value 9 and turns on one of its decimal output.

    The K155ID1, which claims to a replacement for 74141, works like the 74141 and does not outputs anything for BCD code 0A to 0F.
     
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