Hi,
I have a circuit build with an CD4017 which gets a clock signal from a CD4047.
On the CD4017 I connected 4 LEDs behind an ULN2004AD transistor array.

I want the 4 LEDs blink in sequence which works good so far.
The LEDs are connected to CD4017 Q0-Q3 (pins (3, 2, 4, 7), Q4 (pin 10) is connected to RESET (pin 15).
So I want the 4 LEDs to blink and then reset the 4017 and start with Q0 again.

As I said that works quite well BUT the CD4017 is not reset on Q4. There are a few (milli-)seconds black where none of the LEDs is lighting up and then it starts back with Q0. In the "blackout time" the 4017 runs through the ports Q4-Q9 where no LEDs are connected. But I want it to reset on Q4. I don't understand why its not working?

Hope someone can help. I already checked so many topics here (and also on Google) but none of the solutions worked for me...

Thank you.

Circuit diagram (made with easyEDA):
Voltage is +3.7V, not 5V like on the image.

 

On the CD4017 I connected 4 LEDs behind an ULN2004AD transistor array.

What current are the LEDs being operated at?

Circuit diagram (made with easyEDA):

That's a terrible way to draw a schematic. I refer to that style as "netlist style" because it's about as difficult to read as a netlist. Pin order symbols are only useful for showing routing congestion. They do nothing to convey circuit intent.

Will take some time to analyze your "schematic" to make sense of it before I can comment on your problem.

 

The symptom you describe suggests that RESET is not connected to Q4. Check your wiring.
Check using other outputs.

 

Circuit diagram (made with easyEDA):
Voltage is +3.7V, not 5V like on the image.

Pin 6 on the timer is floating.

From National Semiconductor datasheet:

 

You have two outputs shorted together. (CD4047 output pin 13 and CD4017 pin 10).
Use an OR gate or diodes to separate them.

 

The symptom you describe suggests that RESET is not connected to Q4. Check your wiring.
Check using other outputs.

I already tried (all) other outputs but with no effect.
If I manually connect pin 15 to VDD the CD4017 resets but it doesn'r reset when it's triggered over one of the CD4017 outputs.

I have another CD4017 on my board which has the exact same wiring and this one works well.
I already tried another PCB with another CD4017 to see if the chip is broken but I have the same issue on the other board.
The only difference is the clock, the CD4017 which works well gets it's clock from CD4047 pin 10 and the other CD4017 which doesnt work as expected get it's signal from CD4047 pin 13. The reason is that I need the different impulses (pin 13 is double "speed" than pin 10).

 

I have another CD4017 on my board which has the exact same wiring and this one works well.
I already tried another PCB with another CD4017 to see if the chip is broken but I have the same issue on the other board.

Have you tried swapping CD4017?

Post a picture of your wiring. Sounds like a wiring issue or defective counter.

 

Have you tried swapping CD4017?

Post a picture of your wiring. Sounds like a wiring issue or defective counter.

Yes, I tried that already. No effect.
I could post a photo of my PCB but wou wouldn't see anything there because I ordered the board from JLCPCB so most of the wiring is not visible. I also soldered another PCB with completely new parts and it's also not working. So I think the CD4017 is okay, it must be somewhere else.

 

You have two outputs shorted together. (CD4047 output pin 13 and CD4017 pin 10).
Use an OR gate or diodes to separate them.

Sorry but I don't see where there are shorted together?
CD4047 pin 13 goes to CD4017 pin 15 (clock)
CD4017 pin 10 (Q4) goes to CD4017 pin 15 (reset)

Am I missing something?

 

Try testing the circuit first on a breadboard.

 

Sorry but I don't see where there are shorted together?

There's no short. It's just difficult to follow your schematic "style".

Your usage of connector symbols is also non-standard. The ones that point towards the pins are typically inputs and outputs would use a connector that pointed away from the pins.

 

There's no short. It's just difficult to follow your schematic "style".

Your usage of connector symbols is also non-standard. The ones that point towards the pins are typically inputs and outputs would use a connector that pointed away from the pins.

I'm sorry if this confuses you. The use of the symbols is predefined in easyEDA and unfortunately cannot be changed by me.

 

I'm sorry if this confuses you.

It doesn't confuse me. It just makes your schematic more difficult to read and my preference is to just not read them. Yours was simple enough that I decided to try to help.

The use of the symbols is predefined in easyEDA and unfortunately cannot be changed by me.

Crappy tool...

Pin order symbols are almost always bad. The CD4047 timer symbol in Eagle isn't as good as it could be, but it's far better than what easyEDA is using. Those symbols have absolutely no thought given to them.

 

It doesn't confuse me. It just makes your schematic more difficult to read and my preference is to just not read them. Yours was simple enough that I decided to try to help.
Crappy tool...

Pin order symbols are almost always bad. The CD4047 timer symbol in Eagle isn't as good as it could be, but it's far better than what easyEDA is using. Those symbols have absolutely no thought given to them.

Thank you very much, I really appreciate your help. I'm also getting a bit frustrated about what else I can do.

 

I'm also getting a bit frustrated about what else I can do.

Do you have a dual channel oscilloscope or logic probe that you can use to monitor the signal on O4?

Two channel scope because you want to trigger on the clock pulse to be able to see any brief HIGH output on Q4.

 

Do you have a dual channel oscilloscope or logic probe that you can use to monitor the signal on O4?

Two channel scope because you want to trigger on the clock pulse to be able to see any brief HIGH output on Q4.

Sorry I don't have any of those devices. I just have a multimeter.

 

Try testing the circuit first on a breadboard.

I put everything on a breadboard yesterday and tested and everything works perfectly.
On the one hand, this is good because it means that the circuit basically works. On the other hand, bad because the problem still exists.

 

I put everything on a breadboard yesterday and tested and everything works perfectly.
On the one hand, this is good because it means that the circuit basically works. On the other hand, bad because the problem still exists.

What problem?

 

What problem?

The problem with the other board, the CD4017 which does not reset correctly.

 

The problem with the other board, the CD4017 which does not reset correctly.

Here is a simulation showing correct connections (see post #4)