Quote Originally Posted by xnihilo View Post
Hi.

Could somone tell me what should be the values for External weak pullups.
I'm using 10K but I thing it is too much. I read somewere I should use 4.7K.
So what value should I use to be safe?
I have used both values without problems although I normally use 10k.

Do I need to use external pulldown resistors on pins that are default LOW.
Let's say I want RA5 on PIC16F684 to be low by default oce I disable internalm wpu, should I use an external weak pull down resistor to tie it to ground? If yes, what value?
It really does depend on what the input to the PIC is coming from although, generally, it is best to use a pull-down resistor otherwise it mght be left 'floating'.

Should use a RC networks (0.1 capa with an external resistor for weak pull ups or just a resistor?
again, depends on what it is being connected to. Some times it is necessary to use a capacitor to reduce noise etc

I've seen that in some circuit, the designer used a 47 UF capacitor on his 7.2V power supply for supplying a circuit with a PIC16F684. Why would he use this capacitor as the current is DC?? Is it needed to filter something or to prevent some voltage loss or something?
I'm assuming the capacitor was placed across the power supply of a voltage regulator. This is common practice and helps "smooth" the voltage. If I'm using a 5V regulator, I normally have a 47uF or 100uF across the input to the regulator and 10uF on the output of the regulator. Normally, I have 100nF capacitors across both input and output of the regulator in addition to the 47/100uF and 10uF caps. Some may say that this is unneccessary with todays voltage regs. Have a look at the specific voltage regulator data sheet; it may suggest different values.

Hope this helps

Rob