Hello everyone..

I'm trying to do a counter, works on simulation, trying to assemble on board, but I'm having same issue on each IC.
Here is schematic, simplified:


Signal going in is fine,


On pin 13 (Q8), signal is fine,


but on pin 12 (Q9), I get loss of signal.


Normally, I would assume that IC is bad, but I'm getting same thing on 3 different IC's, at exactly same pin..
Any ideas/suggestions?

 

If your reset pin is floating as shown in your schematic, then it is possible that once you get enough stages changing shape the current draw is too much and you get a glitch.

I'd recommend doing two things at this point:

1) Make sure that no inputs are floating.
2) Properly bypass the IC power supply.

 

Yup, grounded reset pin, and it worked. Thank You.

 

Yup, grounded reset pin, and it worked. Thank You.

Just be sure to learn the lesson -- NEVER leave logic inputs floating (unless the data sheet specifically recommends it).

 

With CMOS even inputs of sections of multi-section packages, such as gates, decoders, muxes, etc. should not be left floating. Floating inputs can assume a voltage such that both P and N devices are partially on allowing DC power supply current flow. Floating inputs can pick up enough noise to cause switching. Each time a CMOS output switches there is a brief current pulse, again because both P and N devices are partially on at the same time. If the switching is fast enough, the average current may be significant. Either the DC issue or the pulse current issue can cause a circuit you expect to draw a few microamps to consume tens to hundreds of microamps or even into the milliamp range. This is quite unsatisfactory in battery powered gear.