limiting current

Is there any device that i can connect to my arduino in series with the 5 volt line that will cut power if the voltage exceeds a certain amount?

arduinoPi: Is there any device that i can connect to my arduino in series with the 5 volt line that will cut power if the voltage exceeds a certain amount?

There are ways to limit current and there are way to limit voltage. Controlling one tends to keep the other within a range. So I think you need to make a more detailed explanation of what your are trying to protect from what. The +5vdc on an arduino board is generated by either the on-board +5vdc regulator or the PC's USB port, neither is a likely candidate for generating a voltage excess. And when trying to limit voltage one operates in parallel to the voltage source in question, not in series. One can control or limit current by series methods.

One classic overvoltage protection circuit is the so named 'crowbar' circuit, which is a voltage detection circuit that turns on a SCR that is wired in parallel to the voltage output which shorts out the voltage causing an upstream fuse or circuit breaker to be forced to open or trip off.

So give a realistic scenario of what kind of specific failure you are wanting to deal with and what part of a system you are trying to protect from that scenario. From that better practical protection methods may be forthcoming.

Lefty

thank you for the reply. I have a large robot that will be running off of a 12 volt lead acid battery. The arduino and a bunch of other electronics will be running off of a 5 volt switching regulator. I was hoping to be able to put all of my electronics in groups and have each with a 5 volt cut off device instead of all the electronics running off of the same 5 volt line directly. I want to take this precaution in case of the regulator failing or a short of 12 volts in a 5 volt system. I figured if there was a short it wouldn't ruin all of my electronics which seem to be quite expensive.

arduinoPi: thank you for the reply. I have a large robot that will be running off of a 12 volt lead acid battery. The arduino and a bunch of other electronics will be running off of a 5 volt switching regulator. I was hoping to be able to put all of my electronics in groups and have each with a 5 volt cut off device instead of all the electronics running off of the same 5 volt line directly. I want to take this precaution in case of the regulator failing or a short of 12 volts in a 5 volt system. I figured if there was a short it wouldn't ruin all of my electronics which seem to be quite expensive.

Well you are describing two different failure mechanisms that require two different possible solutions. The protections of all devices from a possible over voltage condition from the single 5 volt switching regulator really calls for a single 'crowbar' type protection circuit located at the output of the switching regulators. Protection from any single module developing a short circuit and causing a over current situation for the 5 volt switching regulator is best met with simple fuses or thermofuse located at the 5vdc inputs to each module or logical subsystem groups.

Here is a make up of a typical overvoltage crowbar protection circuit, many examples should be found on the web if you search them out. http://upload.wikimedia.org/wikipedia/commons/6/66/Crowbar_Circuit.jpg

Lefty

Can we take it that you are using the Atmega chip embedded on a separate board ( rather than an Arduino board ? )

No, I have the Atmega on an arduino board. Is it better if it is not?

If you are using the DC socket of an Arduino board, then 12 volts would not harm it anyway .

I am not using the DC socket I am using a 5 volt regulator that is hooked up to a 12 volt lead acid battery. Here is the regulator. http://www.pololu.com/catalog/product/2111 The power is fed directly through the 5 volt pin and ground.

I would not bother doing anything to protect the output. Normally regulators like that fail open circuit when they fail.