IC decoupling

Hi All
Great to be here
Please be gentle with me I am not as young as I pretend to be !

I have a question (having been out of electronics for nearly 15 years.)

I am building a little circuit that basically is cascade of CMOS bcd counters and drivers for 7 seg leds....(before everyone yells "USE A PIC" ...I don't want to ) the input will be from a hand controlled switch so VERY slow.
So decouple the ic's or not?
I intend to have a well smoothed power supply etc..

If I do decouple, for the ultra low count, I would not even begin to guess a value any ideas?

John

Yes, decouple. 0.1µF monolithic or ceramic is sort of standard. The counting may be slow, but the switching of hi/lo states isn't.

Ken

John_B said:

So decouple the ic's or not?

Click to expand...

ALWAYS - absolutely 100% - decouple the chips, and the supply as well.

0.1uF close to every chip, and a scattering of electrolytics across the board.

Don't forget debouncing on your slow input as well.

You might also want to put a 10uF tantalum (or ceramic) close to the LED driver supply voltage. If all your LEDs switch on at once, it could cause some bounce on the LED supply voltage. A 10uF will provide a low impedance path for the initial surge of current. Was that gentle enough?

Beautifully gentle

Thanks guys for all your input.
Somehow I gotta find some room for the caps *S*....I must admit I was expecting to decouple just hopeful I wouldn't !

Hopefully I will be able to offer input to the group not just getting stuff out !

thanks again.....

John