A 555 will not do anything if its pin2 is connected to ground. Pin2 normally connects to pin6 and the timing capacitor.

If you want the CD4017 to stop after 9 outputs then connect the 10th output to a transistor inverter that resets the 555's pin4.

Apologies. I should have said the negative side of the timing cap would be connected to ground.
Regarding the transistor inverter, are you referring to pin 4 of the 555 oscillator that's on the chaser board, or the 555 monostable that will be switching power to that oscillator? I thought of the same thing, sort of. I was going to try a NPN on the 10th output (resetting pin 4 of the 555 monostable) but leave the LED in there as well. I'd prefer to get all 10 LEDs lighting if possible. I can live with 9 outputs if necessary, though. Thanks again!

 

If the 555 is reset on the 10th output then the LED on the 10th output will light for such a short amount of time that you will not see it light.

I have some chaser projects that use Cmos Schmitt-trigger oscillators (not 555 oscillators) and they chase around and around a few times (with a pot to adjust the speed) then a pause before chasing again. Each LED lights brightly for a short duration to save battery power. 2 or 4 AA alkaline cells last for months.

 

Tanks guy, I'm gonna steal that one. My little CMOS flasher is still going, almost 2½ months later.

 

A 555 will not do anything if its pin2 is connected to ground. Pin2 normally connects to pin6 and the timing capacitor.

If you want the CD4017 to stop after 9 outputs then connect the 10th output to a transistor inverter that resets the 555's pin4.

I finally got back to this project (different application) and have a quick question.
Audioguru, you suggested using a transistor inverter to shut off the 4017, using the output from one of the pins to pull down the reset pin (4) on the 555. I built an inverter per the schematic at the bottom of this page:
http://www.kpsec.freeuk.com/trancirc.htm
but I'm unsure how to attach it to the chaser circuit. Connecting the 4017 output to the base resistor is straightforward. The reset pin of the 555 is currently connected to V+. Should the inverter's output connection just go to the 555 reset pin? And I don't understand how the 555 would be re-started. Could that be handled by a momentary switch that pulls pin 2 to ground? As always, thanks much for the help.

 

A 10k resistor from pin 4 of the 555 to the positive supply makes it high so the oscillator runs then the collector of the transistor makes it low to stop the oscillator. If the transistor is driven from another but slower 555 oscillator then it will turn on and off to make the chaser circuit go on and off.

The 555 does not run when the reset pin is low. Grounding pin 2 will not start it.

 

Thanks Audioguru. Let me explain what I need this circuit to do. I need to be able to start the chaser with a momentary switch, and have it shut off when it reaches a given output pin on the 4017, in this case output 9. It looks like the inverter circuit will pull pin 4 of the 555 to ground for an instant, stopping the 555 (and the 4017). But as soon as output 9 of the 4017 goes low, would the 555 start up again? Should I be controlling the oscillator's power with a second 555, configured as a monostable timer, and use the inverter to reset the monostable timer?

 

When output 9 of the CD4017 goes high then the transistor resets the 555 then the counter stops forever with the 555 continuously being reset.

You could have the output 9 capacitive-couple a pulse to set a flip-flop that resets the 555 then an external switch can reset the flip-flop that starts the 555 oscillating again.

 

I had another thought - I could use a monostable 555 to switch power to the chaser board. Dial in the one-shot to match the 0 through 9 sequence time (tedious), or use the inverter on output pin 9 to shut down the monostable timer.

 

I must have something wrong here (no surprise). I built the inverter per the schematic that I linked to in an earlier post, and as far as I can see, it's wired in correctly. I have the voltage signal from output 9 on the 4017 going to the base resistor of the inverter. Pin 4 on the 555 is connected to the inverter output. The 555 timer, the chaser board and the inverter are on the same power source. When the 4017 increments to the last output, the 555 doesn't shut down. For some reason, pin 4 is not getting pulled to ground. Anyone have any thoughts on this? Thanks for all advice.

 

This reply replaces the one I just deleted:
We don't know the part number of the transistor you used and we don't know if you connected its pins backwards.

 

Sorry - I used a 2N2222 NPN and double-checked the pinout to be sure I got it right. I did have a thought - I built it to the schematic I found online and it called out a 10K base resistor. I checked the voltage at the outputs on the LED chaser board and they are ~2VDC. Perhaps the 10K resistor is a bit high?

 

We forgot that the outputs of the CD4017 are loaded down with the current in the LEDs.
The 10k base resistor is fine when the collector resistor is 4.7k to 10k.

 

Hmm...per the schematic I used a 1K collector resistor. Should that value be higher? I should also mention how this whole thing is powered. I'm using a 12VDC 1A regulated supply for the 555 and a LM7809 to power the chaser board. It was supposed to be powered with a 9 volt battey, so I'm tapping the 12VDC supply for the LM7809. The 555 controls a relay that switches the 9VDC to the chaser board.

 

The output signal voltage of the 555 is too high for the CD4017. The input signal voltage to a CD4017 must never be higher than its supply voltage. So maybe the CD4017 is destroyed.
Use 12V as a supply voltage for the CD4017 to fix it, then re-calculate its LED current-limiting resistor. The 9V regulator is not needed and is not wanted.

The reset pin of a 555 draws no current when it is high so a 10k resistor to the positive supply will turn it on and an inverting transistor to ground will reset it. Your inverting transistor has a very low voltage driving its series base resistor but the transistor can drive the 10k collector resistor plus the reset pin's logic-low current.

 

Thanks Audioguru, I really appreciate your help with this.
The 4017 is not getting it's input signals from the 555 monostable circuit. There are two 555's in this circuit - a monostable timer that controls the time the chaser board is turned "on", and a second 555 (astable) that sends the input signals to the 4017. Both the astable 555 and the 4017 are running on 9VDC (via the LM7809). The monostable timer does run on 12VDC but it's output is isolated from the 4017 by the relay. The two circuits, the monostable timer and the astable + 4017 do share the same ground, however.

 

OK, got it. I sent the high pulse from the 4017 output pin #9 to a 250 ohm base resistor on an MPSA13. I attached pin 4 of the 555 monostable timer to the collector pin and wired the emitter back to the ground on the LED chaser board. The 555 monostable timer shuts off power to the chaser board when the 4017 increments to the #9 output pin. The only thing I'm not comfy with is that pin 4 of the 555 appears to be floating - as you all know it's usually attached to V+. Not sure how to get around this, but it's working fine.

 

A 10k resistor from pin 4 to the positive supply for the 555 pulls it up when the transistor is turned off. The resistor is called a "pullup" resistor.