Series resistor when using weak pull-up

[Sharky]

Hi, I am designing a board that is connected to a momentary switch,
normally i just use a pull-up resister and a series resistor and a capacitor,
the series resistor and capacitor work as a low-pass filter to suppres noise.

See the attached drawing.


But now I want to use the weak pull-up, so I just removed R1 and programmed RA4 to have weak-pull-up but it don't work if I still use R2!

Should I remove R2 or just use a smaller resistor.

Sharky

[sayzer]

Hi Sharky,

Weak pull ups work on PORTB.

Also, for some reason forum servers have some issues with attachements now.


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[Sharky]

Hi Sharky,

Weak pull ups work on PORTB.

Also, for some reason forum servers have some issues with attachements now.


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Hmm, really on the 16F630 I use it work on PORTA. :)

I am not having problems programming the weak pull ups.
I just want to know if I should use a serie resistor and a decoupling capacitor
as I do when I use an externally pull up resistor.
Because if I use a 10K serie resistor as I use to do, it does not work!

Yes, I can see that it is impossible to view my attachment, but I don't know why?

Sharky

[sayzer]

For PIC16F630, PORTA weak pull-ups OK!

No schematic, bad guess.

Forum has some issue.

Let see your schematic if you can upload it to http://picsplace.to and then put the link here.


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[Sharky]

For PIC16F630, PORTA weak pull-ups OK!

No schematic, bad guess.

Forum has some issue.

Let see your schematic if you can upload it to http://picsplace.to and then put the link here.


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Here is the link:

http://img4.picsplace.to/img.php?file=img4/26/weakP.JPG

Sharky

[mister_e]

1. 10K is too high. <1K could do... usually not needed.

2. the capacitor is usually useless as you can do the debounce in software in most case.

[Sharky]

Hi Mister_e,

I normally do the debounce in software.
I have always used capacitors on inputs to suppres noise, but maybe they are not necessary?

Sharky

[mister_e]

i don't remind to have used capacitor on any of my design to supress noise when debouncing and handling could be done in software.

Now if your buttons are far of your main board, it's another story.. but even in this case, i doubt capacitor will do some magic stuff.

Maybe someone else have another point of view?

[Sharky]

The touchpad that is connected to the board have 1.5 metre of cable.

I have only used the capacitors and the serie resistors for products that needed
to have an approval.

But if I understand you right you also mean that the software debouncing will do the job.
I think that I will just try to make the board without capacitors and serie resistors on the input's and see what happen when it goes to approval.

Sharky

[mister_e]

So in this case don't use the internal weak up. Use 1K-4.7 K instead. Safer.

It's a long debate...'to use or not to use internal pull-up?'

[Sharky]

I have used pull-ups up to 100 K without problems.

I know that you don't like weak pull-ups I remember from one of my other thread's, but I would really like do know what the problem about them should be?

Because I really can see myself save some space on my PCB if I use the WPU's
but if it is to risky I will of course not use them, I would just like to know why I
should not use them!

I have read that Melanie often use them even in industrial applications and I must admit that a lady that have a catsuit gives even a Shark some respect! :D

Sharky

[sayzer]

...and who is being the Shark here, I really wonder? :)


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[mister_e]

so you should know a part of the story. I had some issue in car application, after i switch for external one i nerver ever had issue... this is why.

BUT if it works for you... use it.

Also, don't forget, if the unit is not always powered.... there's no pull-up, those pins comes 'floating' ...

But i'm from the old school. I have my own fear that some don't have. ;)