nte 2018 not working

[ChrisP58]

Decoupling caps are typically 0.1uF ceramic caps place close to the poser supply pins of the logic IC parts. When the pins change states from 1 to 0 and back, the ICs draw very short spikes of current. The spikes are only a few picoSeconds long so there is very little energy in them, but they can cause glitches that make logic circuits misbehave. The decoupling caps prevent these little current spikes from affecting Vcc but providing local power storage.

Ideally you would have one cap per IC. But if you have a good PCB layout with a ground plane and low-z vcc traces, you can often get by with one cap per 3 or 4 ICs.

I'm not sure what you mean about replacing the 138 decoders with a decade counter. The two functions are not directly compatible.

 

[ebb]

this is what you wrote about replacing the 138 with decade counter
The pinout is the same for both the 138 and 238. The symbol difference is only that the 238 won't have bubbles on the outputs.

Make sure that all input pin are tied either to another output, or +5v or ground. No logic inputs may be left floating!!!!

You will need to add decoupling caps to the layout.

Your schematic shows the ULN2801. If that is what you will be using you need to add a 2.7K resister in series with each ULN2801 input. The ULN2803 already has that resistor.

You can replace the two hc138 parts with a single HC42 decade decoder.

 

[ChrisP58]

The 74HC42 is a decade decoder, not a counter.

Here is the updated schematic using the HC42.

Looking this over I see a possible problem. Output 00 will be on when the system is reset even before the first clock pulse. As such, it may not be a usable output for you.

If you really need 80 outputs, you may need to go back to the two HC138 decoders to get an 11th enable to drive one more HC238 output decoder.