Reset switch of CD4017 counter doesn't work properly on my circuit, why?

Discussion in 'Digital Circuit Design' started by nornandxor, Jul 11, 2018.

  1. nornandxor

    Thread Starter Member

    Dec 11, 2017
    145
    7
    Hi,
    Below is the circuit that where I have the cd4017 counters and the Reset switch connected to the GND through a resistor. The issue is it doesn't work on my breadboard unless I remove the Resistor and just short the wire directly to the GND, at that time the Reset switch works!!!
    I tried a variety of different resistors ranging between 150 ohm to 1 Million ohm and none of them worked!
    Any idea why this happens!
    wq.JPG
     
  2. nornandxor

    Thread Starter Member

    Dec 11, 2017
    145
    7
    Do I really need to add a Resistor there if the Reset switch works without it? I had the Resistor there because thats what I keep seeing on other similar circuits online! Is it because the counters I'm using are SMD's or it doesn't matter?
     
  3. Sensacell

    Moderator

    Jun 19, 2012
    1,897
    572
    You need a resistor.

    Did you check the voltage on the reset pin?

    Check it with both switch open and closed- post your findings.
     
  4. ScottWang

    Moderator

    Aug 23, 2012
    6,250
    970
    R1 = 4.7K(or 5.1K) for +5Vcc,
    R1 = 10K(or 9.1K) for +9Vcc,
    R1 = 12K for +12Vcc.

    Please measures the Reset Switch to make sure that it is works fine and also check two wires which connected to the Reset Switch.

    Please measures the voltage of the pin 15(MR) when the Reset Switch is pressed and before you press it.
     
  5. nornandxor

    Thread Starter Member

    Dec 11, 2017
    145
    7
    Thank you guys for the help! I will do the measurements and update you with the results.
     
  6. danadak

    Well-Known Member

    Mar 10, 2018
    1,429
    292
  7. nornandxor

    Thread Starter Member

    Dec 11, 2017
    145
    7
    Thanks Dana,
    I appreciate your insight but I dont have enough time to go through prolonged articles! Thats why we have our lovely allaboutcircuit, the best quick problem solving tool ;)
    Also, I already have a solution for the bouncing issue, I paralleled the switch with a capacitor and thats it!
    Thanks again and please keep me updated with your thoughts and insights because I truely believe that you guys are the best compared to all other online forums and other websites! ;)
     
    Last edited: Jul 12, 2018
  8. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
    7,003
    1,985
    I don't think this is the problem, but you should add decoupling capacitors to each IC. 0.1 uF to 1.0 uF, preferably ceramic, from pin 8 to 16 with the shortest possible leads.

    Unless you are counting an input in the kilohertz frequency range or higher, bounce on the reset input will have no effect on the operation of the counter.

    What is the input signal? Frequency, pulse width, etc?

    ak
     
  9. danadak

    Well-Known Member

    Mar 10, 2018
    1,429
    292
    CD4017 timing restrictions -

    upload_2018-7-12_11-51-59.png

    and

    upload_2018-7-12_11-52-42.png

    Irrespective of frequency....

    Regards, Dana.
     
  10. crutschow

    Expert

    Mar 14, 2008
    19,515
    5,440
    Even if the switch bounce violates any of those switching parameters, that input is level sensitive not edge sensitive, and the final DC value of the switch will be the logic level that the IC will respond to at the end of the bounces.
    Bouncing of the reset signal is not his problem.
     
  11. danadak

    Well-Known Member

    Mar 10, 2018
    1,429
    292
  12. RichardO

    Senior Member

    May 4, 2013
    2,270
    878
    Are you sure that the reset signal is subject to metastability?
     
  13. danadak

    Well-Known Member

    Mar 10, 2018
    1,429
    292
    Neither sure nor unsure, did not design the 4017. So best advice is adhere to data
    sheet specs and best practices ? Runt and ill formed logic pulses not best practice.

    Regards, Dana.
     
  14. Sensacell

    Moderator

    Jun 19, 2012
    1,897
    572
    I agree that bouncing on a level-sensitive input is highly unlikely to be the problem.
     
  15. nornandxor

    Thread Starter Member

    Dec 11, 2017
    145
    7
    Some updates:
    - I couldn't get any measurements from Pin 15 (on both IC's), it just showed me 0mV, though circuit's output seems fine.
    - Again, Reset switch works only when resistor value is either 0 or a few ohms.
     
  16. ScottWang

    Moderator

    Aug 23, 2012
    6,250
    970
    So now you have to use Ohm meter to measure all the wiring about the Reset Switch, R1, MR(pin 15), and to make sure that the Reset Switch itself is fine.
     
  17. nornandxor

    Thread Starter Member

    Dec 11, 2017
    145
    7
    I changed the Reset switch, but I will start checking the wiring again, though I did many times!
     
  18. ScottWang

    Moderator

    Aug 23, 2012
    6,250
    970
    When the Reset Switch is pressed then the voltage of MR(Pin 15) should be as +Vcc.
    And you haven't show how many volts that the Vcc is?
     
  19. nornandxor

    Thread Starter Member

    Dec 11, 2017
    145
    7
    my input voltage is 3V. Everything is on a PCB now, SMD's components.
     
  20. crutschow

    Expert

    Mar 14, 2008
    19,515
    5,440
    If you read you referenced material you will see that metastability occurs in clocked circuits when an input data change to a latch occurs near a clock edge, and the bistable circuit goes into a metastable condition. However, it eventually goes into one of its two stable states..

    So a ratty signal to a DC latch set/reset input could theoretically cause a momentary metastable state but it has to eventually go to the commanded state. A latch cannot indefinitely stay in the metastable condition or stay in an illegal state.
    You are worrying about an issue that does not apply here.
     
Loading...