I was trying to build an analog counter with chips I had on hand, and then it got out of hand. I breadboarded this circuit and it worked, I built a protoboard from it and it worked until I mounted it and then a section went dark. Now Ive rebuilt the board twice and I cant get it to work at all. Here is the wiring diagram, is there something inherently wrong with this circuit that would make the chips fail? Not shown in the diagram but all the LEDs were grounded with 200 ohms so they were receiving around 15 milliamps. Thanks for any help!

 

For one thing, you are missing proper power-line filtering. Put a 0.1 μF ceramic disc capacitor between +V and GND at every IC. Also add a 10 μF electrolytic capacitor between +V and GND.

Don't leave any input pin not connected to something. You have one CD4017 chip with pin-15 not connected.

 

For one thing, you are missing proper power-line filtering. Put a 0.1 μF ceramic disc capacitor between +V and GND at every IC. Also add a 10 μF electrolytic capacitor between +V and GND.

Don't leave any input pin not connected to something. You have one CD4017 chip with pin-15 not connected.

Thank you, I will filter the ICs and the power. So If I am not using one of the LED output pins, should run that pin to ground? The missing pin 15 is connected pin 11 of the last chip on the board. I accidentally left it off of the diagram.

 

Check to be sure that outputs from I.C. components are not connected directly together.

 

Here is a wiring diagram with your suggestions and the LEDs shown. This helps show the unused pins.

 

Well, if you breadboarded it and worked, and the protoboard worked, then the circuit logic would seem to be ok.

From the datasheet it seems that at 15mA you are exceeding the output current limit, so perhaps the chips are failing due to that.

 

Well, if you breadboarded it and worked, and the protoboard worked, then the circuit logic would seem to be ok.

From the datasheet it seems that at 15mA you are exceeding the output current limit, so perhaps the chips are failing due to that.

Is that the current limit on the 4081B or the 4017BE? I wasn't sure about what kind of current was gong into the 4081B. Only one LED is ever active at a time so I thought the 4017s were good.

 

Thank you, I will filter the ICs and the power. So If I am not using one of the LED output pins, should run that pin to ground? The missing pin 15 is connected pin 11 of the last chip on the board. I accidentally left it off of the diagram.

Do not connect to unused outputs.
Think of inputs as ears and outputs as mouths. You do not want to gag someone by sticking something in their mouth.

 

So If I am not using one of the LED output pins, should run that pin to ground?

No. That is not what he said. Re-read post #2.

Something true about almost all IC's, all logic IC's, and especially all CMOS logic IC's, is that there should never be unused *inputs* not connected to anything (floating). An unused input should be terminated high or low, depending on the pin function.

ak

 

Do not connect to unused outputs.

Got it, thanks! I was thinking all ports and not just in-put.

 

Got it, thanks! I was thinking all ports and not just in-put.

One more way to think about this. An output is a voltage source.
Do you really want to connect a voltage source to ground?
Absolutely not.

 

Only one LED is ever active at a time so I thought the 4017s were good.

You should always have the datasheets to hand when designing a circuit. Here's the CD4017 specs for output:



A long way short of 15mA.

 

You should always have the datasheets to hand when designing a circuit. Here's the CD4017 specs for output:

View attachment 330876

A long way short of 15mA.

sorry the top is getting cropped off there, which column is showing the amperage? The voltage drop across these LEDs is around 2.9 volts

 

... which column is showing the amperage?

You still don't have the datasheet to hand????

Here you go:

 

The data sheet shows the current available while maintaining a certain output voltage.

You can get more current from the outputs but with a lower output voltage...the frustrating thing is not being able to get the power ratings of an output pin.

So, for example, at 12-volts VDD you could get 10mA from an output, but the output voltage might be 9 volts, so the power would be .030 watts.

Then you have to consider how long an output is active per second...blah blah blah...etc.

I have gotten 10mA from 4017Bs in many projects. (but not at 6-volts VDD)

If you were actually limited by the current ratings in the datasheet, you wouldn't even be able to drive a transistor into saturation with more than a few mA of collector current.

 

Oh, one more thing. You cannot use an output to drive an LED and drive another logic circuit at the same time.
You need to buffer the logic signal separately to drive the LED, otherwise the LED is going to disturb the logic output.

 

I have gotten 10mA from 4017Bs in many projects. (but not at 6-volts VDD)

So if I drop my LEDs to run on 10mA which is fine, and take my supply up to 12 volts, do you think the 4017Bs will take it?

 

So if I drop my LEDs to run on 10mA which is fine, and take my supply up to 12 volts, do you think the 4017Bs will take it?

I would leave it as is and look for a different problem.

 

In your second diagram you have your 104 caps in series with the positive power inputs...that's not correct, they should be across the power pins.

It also looks like the 10uf cap is connected wrong.

 

You are using Q0 to cascade your CD4017 counters?
You should be using CARRY OUT instead.