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For days I've tried to create a simple led walker using a 555 and 4017 IC, with a 9v battery.

My latest attempt was from the electronics for dummies book: enter image description here enter image description here

I'm not using these exact values, instead of a megaOhm potmeter I'm using a 100k resistance for example, and using a polarized capacitator for C1. Doesn't seem to matter for the results, I've tried all kinds of combinations of resistances and capacitators for the 555, getting very slow to very fast output signals. That's not the problem.

The problem is that the 4017 isn't doing anything. It starts up in a weird state where 3 leds are on at the same time, and nothing happens. In this pic I hooked up a led and speakers to see if I get a good signal from the 555 (you can see 3 leds are on, on the right side): enter image description here

This is without the leds hooked up: enter image description here

Things I've tried:

  • replacing the 4017
  • varying the 555 signal speed
  • removing the led/speakers from the 555 output so its only connected to the 4017

I'm out of ideas so hopefully someone can help me troubleshoot this.

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  • \$\begingroup\$ Can you use a voltmeter or oscilloscope to look at the 4017 output signals without the LEDs connected? Do they rise and fall with the clock input as you would expect? If they dont, use a voltmeter to check that the voltages on the input pins are what you expect. \$\endgroup\$
    – InBedded16
    Commented Jul 16 at 16:44
  • \$\begingroup\$ You don't use the reset input to achieve a start condition, all internal flipflops set to zero. The weird state where 3 leds are on is cleared by reset. \$\endgroup\$
    – Uwe
    Commented Jul 16 at 16:52
  • \$\begingroup\$ 4015, 4017 or 40175? The IC number in the header, in the body text and on the IC package should be equal. \$\endgroup\$
    – Uwe
    Commented Jul 16 at 16:57
  • \$\begingroup\$ Fixed the title, cant believe I got a completely different IC by asking for a 4017 \$\endgroup\$
    – Oli
    Commented Jul 16 at 17:00

1 Answer 1

Reset to default
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Enhance

40175

A 40175 is a quad D-type flip flop. You need a 4017. And power supply decoupling capacitors.

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  • \$\begingroup\$ Thanks, any specific number or type I should look for? Also, what kind of value for the capacitator, and is it really needed? \$\endgroup\$
    – Oli
    Commented Jul 16 at 16:55
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    \$\begingroup\$ Just some type of 4017 that's compatible with the voltages and currents you're running; speed isn't an issue for this application. I would do a small electrolytic (~10 µF) where the power leads enter the board and then some smaller ceramics (0.1 µF) across the power pins of each individual chip. Digital logic circuits driving LED like this are an excellent way to observe the effects of insufficient power supply decoupling. \$\endgroup\$
    – vir
    Commented Jul 16 at 16:59
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    \$\begingroup\$ 40175, excellent catch! \$\endgroup\$
    – Uwe
    Commented Jul 16 at 17:01

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