1
\$\begingroup\$

I'm trying to build a 13 count johnson ring counter (which flashes LEDs sequentially 1 thru 13 and then repeats), and I found this circuit which looks perfect: 4017 johnson counter

I assembled it with an extra LED on the 555's output pin. Oddly, when I apply power, this LED stays solid on, while none of the outputs of the 4017 are lit. In trying to troubleshoot this, I noticed that the wiring of the 555 differs from all of the standard implementations described on wikipedia (astable, monostable & bistable). QUESTIONS:

  1. Does anyone know if this is a reasonable way to use a 555? The commenters on the aforementioned post seemed to think it was.
  2. Otherwise, if you see it to be faulty, can you suggest an appropriate fix for this circuit? I tried a normal astable setup and got nothing, but I have to admit that my understanding of what the AND gates are doing is too foggy to know if this should work.

Thanks in advance for you help!

Edit: discovered a loose ground to the breadboard with the LEDs. Plugged this in, and now I see that a few of the LEDS are lit -- flickering & different brightnesses -- mostly on the second 4017. Totally stumped.

\$\endgroup\$
8
  • \$\begingroup\$ what value are you using for that anonymous cap in the diagram bottom right? I'm not sure what it should be doing, but a large enough value might prevent the 4017s from clocking? \$\endgroup\$
    – Neil_UK
    Dec 25, 2015 at 8:45
  • \$\begingroup\$ @user44635 It's a 100nF, value stuck between the two diodes, up and down. \$\endgroup\$
    – user59864
    Dec 25, 2015 at 9:10
  • \$\begingroup\$ The schematics would be much easier to read if the pin names were also there. \$\endgroup\$
    – user59864
    Dec 25, 2015 at 9:11
  • \$\begingroup\$ Instead of using this circuit which you don't fully understand, build the logic for johnson counter with discrete D- flip flops. \$\endgroup\$
    – ammar.cma
    Dec 25, 2015 at 9:40
  • \$\begingroup\$ @G Math 100nF ! that's a hellauv big value. What's it's supposed to do??? \$\endgroup\$
    – Neil_UK
    Dec 25, 2015 at 20:50

0

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Browse other questions tagged or ask your own question.