Utility of 0,1µF capa when batteries are used

Hello,

It is well known: always connect a 0,1µF between VDD and GND on a PIC!

I'm curious to know if this is still needed when the kit is powered with batteries?

If yes, what would be the reason?

Hi, Roger

Why do you always want to rebuild the world ???

Just take a scoping of the supply lines on the PIC pins ... and watch the difference ...

In certain configs no cap doesn't really matter ... in others you can't do anyting with your PIC. Batteries or not batteries.

( I MEASURED a half full 4 Sanyo 2100 mAh NiMh AA cells batt @ 0.45 Ohm internal resistance ... 78L05 does much better !!! )

If you need ONE good reason ... consider RFI generating on supply lines AND RF Generation.

Alain

Yes they still would be needed, The reason they are needed is they are known has decoupling capaictors, Thelp help prevent noise which could effect the pic or any other part of your curcuit it aslo helps out with the EMC rules, The normal rule every IC is best to have a 100N(.1uF) cap has close has possible to the IC power pins.

There may be more reason but these are the simples ones

Okay, okay guys, I was just asking...

Gonna have a look at this with a scope.

Is this capacitor that usefull, it should be embeded in the PIC, no?

Thanks a lot for your remarks and interresting infos.

Every switching circuit needs the caps.

Think of the internal circuits of the output pin either PIC or a TTL circuit. It conducts Vcc to the output then this transistor is put in off state and the other to the ground is switched on.

In an ideal world this is what should happen. But the world is not as ideal as we wish to be, so there is a small fraction of time where these two little transistors conduct at the same time producing a power drop.

You can see this in the scope clearly. Put the capacitor and all will be much cleaner. Power source has little to do with this, batteries being better in that they do not try to correct the drop by raising the level and then producing overshot.

Hope is more clear now.

So, bottom line:

Whatever you do use always capacitors!

Ioannis

Thank you again for being that clear.