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We are trying to create a chaser circuit using a CD4017 counter with the output of a 555 timer as the CD4017's input. The schematic diagram used is here (photo taken from circuit digest):

enter image description here

When probing the outputs, we get this waveform

output waveform

Can someone explain why or what causes the /\ /\ /\ /\ /\ portion on the output waveform?

[edit]

Probing the output of 555 and the capacitor produces these waveforms: output waveform of 555 and capacitor

Unfortunately, we weren't able to include both the output waveforms (that of the 555 and CD4017) at the same time on a single display. (lol :( ) Also, we forgot to set the traces on the same volts/div and sec/div

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  • \$\begingroup\$ Hard to say without more info. But it appears to occur around the time of each clock from the 555. Can you now add the 555 output to your scope picture? (I'm wondering about proper bypass caps on your ICs and if all this is wired on a protoboard. Plus, I'm curious about the power supply you are using, as well.) \$\endgroup\$
    – jonk
    Commented Nov 23, 2016 at 11:06
  • \$\begingroup\$ hi! thanks for the response. sorry, i do not have a picture with both of the outputs from 555 and 4017 put together on the same panel. Also, everything is wired on a breadboard and we are using a constant DC voltage supply (~9V) \$\endgroup\$
    – nooble
    Commented Nov 23, 2016 at 12:06
  • \$\begingroup\$ What's a "chaser circuit"? If you just have a oscillator driving a counter, then you should get a sequence of square waves, each half the frequency of the previous. Which output produced the top waveform? How does the time scale relate to the oscillator period? What voltages? \$\endgroup\$
    – Olin Lathrop
    Commented Nov 23, 2016 at 12:29
  • \$\begingroup\$ I see no chip power decoupling capacitors. \$\endgroup\$
    – Andy aka
    Commented Nov 23, 2016 at 12:34
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    \$\begingroup\$ @OlinLathrop The 4017 is a decade counter with ten outputs that go HI in sequence from a source of pulses is connected to the CLOCK input. The outputs are one at a time, so they "chase." \$\endgroup\$
    – jonk
    Commented Nov 23, 2016 at 12:45

1 Answer 1

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My guess, and I cheerfully admit it is a guess, is that you have a bad or missing connection to the Vdd power supply pin on the CD4017.

Power then would being supplied via the 555 through the input protection network on the CD4017.

That could account for the apparently floating outputs when the 555 output goes low.

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