CD4017 sequencer used as a continuity tester

Discussion in 'General Electronics Chat' started by vixr, Aug 21, 2014.

  1. vixr

    Thread Starter New Member

    Jul 16, 2010
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    Hello all,
    long time lurker, first time poster.
    I have a few questions about THIS schematic from an old thread here. The thread is too old to resurrect. My question is: Can this sequencer be used to perform a continuity check? I plan to etch a PCB using the schematic and at the point where Q1-25 goes to ground at pin one, I want to run the signal out through a 30 gauge wire and back to the PCB. Hopefully giving me a lit LED if the wires and slip ring connections in between are good. Will this work? I could test the whole 48 wire slip ring in under a minute instead of the hours it takes to do it with a DMM and interpret the wiring diagram...
     
  2. vixr

    Thread Starter New Member

    Jul 16, 2010
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    My other question is if two slip ring connections are shorted, will it fry the output of the CD4017?
     
  3. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi vixr,
    If two or more slip rings are shorted, wouldn't that be a slip ring wiring failure.?
    I would suggest you consider including a shorted ring test to indicate the location of the short.
    E
     
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  4. vixr

    Thread Starter New Member

    Jul 16, 2010
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    ericgibbs,
    thank you for the quick reply. I only asked about shorted rings so I wouldnt hurt a CD4017... I have not seen many shorted rings, maybe 4 circuits in 5 years. Usually the contacts in the slip ring are intermittent or the pin/wire in the connectors are open.
     
  5. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    Hi,
    If each 4017 output has a limiting base resistor as shown in the circuit, then a shorted ring would not damage the 4017.

    Do you plan to watch the LED's stepping thru while the ring is being tested or some other method.?
    E
     
  6. vixr

    Thread Starter New Member

    Jul 16, 2010
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    Yes, visual... I am hoping a 1Hz clock signal will be long enough to see any open wires. I'm actually going to build two 25 led testers and house them in a single enclosure with a latching pushbutton for each tester. That way I can watch the sequence as long as I wish, then watch the other.
     
  7. RichardO

    Well-Known Member

    May 4, 2013
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    It looks like the circuit you found will cause and LED to go out if the contact is open. It seems to me this may be backwards. I think it would be easier to see an LED come on only if a contact is bad.

    If an LED comes on when a bad contact is detected then you can stop the test at the failure. This will leave the LED on at the first bad contact detected.
     
  8. vixr

    Thread Starter New Member

    Jul 16, 2010
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    Sir,
    Please continue...How would that best be done?
     
  9. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    3 or 4 hex inverter chips.
     
  10. vixr

    Thread Starter New Member

    Jul 16, 2010
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    Ahhh... I think I see. Like a SN7404? the datasheet shows if input is high, output is low. So the SN7404 would go inline between the end of the wire under test and the LED?
     
  11. RichardO

    Well-Known Member

    May 4, 2013
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    How embarrassing. I really haven't thought that far.

    Maybe sense when an LED is on (or not on?) by sensing the current through the LED current limiting resistor and stopping the 555 timer from oscillating. There might have to be an R/S flip-flop involved...
     
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