Arduino Reset Pin - Is A Resistor Needed?

Forum 2005-2010 (read only) Hardware Interfacing
1

The title says it all... Do I need a resistor for a button on the reset pin? I would say yes, but I'm not sure. Do I need just a button, or do I need a resistor liek in the "Button" example?

2

Yet another fine subject to do some research into basic concepts of the fascinating world of electronics. Here's some fodder for Google - I hope you can type that in yourself:

Current limiting resistor
pull-up resistor
pull-down resistor
Ohm's law

And always a good place to look for answers of this kind is the data-sheet of the ATmega8 processor. If you don't have it, get it and read it. If you have it, open it and read it.

Korman

3

I have no idea if it's true for all AVR processors but the ATmega8 does not require an external pullup resistor. Figure 14. Reset Logic in the datasheet indicates that there is an internal pullup resistor.

However, it will not hurt anything to include an external pullup resistor.

The Button Tutorial shows a pulldown resistor.

4

Spoilsport, he could have opened the data-sheet on his own.

Korman

5

Spoilsport

I appreciate the restraint. I've been called far worse (but not here).

he could have opened the data-sheet on his own

That seems a bit cruel to me. The reset pullup is not actually mentioned in the text so there is no way to search for it. You have to carefully look at each figure involving the reset logic to find that resistor.

In my case, the hard work was done by someone else. I simply remembered reading about the internal reset pullup here..
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1284139304/2#2

(Thank you RuggedCircuits! That bit of knowledge has helped me!)

6

There are some web sites that suggest you can do without it. However there have been people who have had trouble with a stand alone system having not fitted. It's only a resistor so why not put it in.

7

It's only a resistor so why not put it in.

I can think of only one reason: It physically won't fit. I'm trying to sqeeze a processor and electronics into the space occupied by a AA cell.

Other than that, the peace of mind is definately worth the 2 pence.

8

It physically won't fit.

Can you use an SMD resistor? That can go just about anywhere.

9

Can you use an SMD resistor? That can go just about anywhere.

Excellent idea! Only two problems: I don't have any. The hardware works and I'm not touching it!