Lynx {Glenn Jones} wrote:
> Sorry this is off topic, but i think that this can help many people
> who arent experts at electronics, and it is related to pics, in a way.

Yes!  Some of my old electronics around the house predate my
understanding of the need for decoupling capacitors.  And CMOS input
pullups!  Every now and then something stops working and I have to
figure out where I went wrong ten years ago.  The latest failure was the
connection from an optocoupler after a motion detector into a CMOS input
that was read by the "alarm" system.  I had no pull-up on the input, the
optocoupler was simply connected directly to ground.  Being woken up at
night is a very good way to refine my designs.

> Anyway, My questions are, what are decoupling capacitors needed for?

They decouple something.  Like a train.  Disconnecting the circuit from
the induced noise from outside.  ;-) ;-)  [i.e. I don't know]

> What value works best?

0.1uF

> Which chips should i make sure to decouple?

Anything with a counter, flip-flop, or oscillator is my rule.

> What are signs that decoupling capacitors are needed?

Spontaneous resets.  Resets or unexpected behaviour when you stick a
transmitting mobile phone near the circuit.  Unexpected input data when
an output is driven.

--
James Cameron                                      (cameron@stl.dec.com)

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