voltage limiter or regulator

I send unstable voltage to my arduino uno which maximum voltage 5V , I want to use a controller or a limitteur voltage to obtain a fixed voltage, what do you suggest ??

Is it high enough for the on-board regulator on the Vin pin?

KeithRB:
Is it high enough for the on-board regulator on the Vin pin?

It’s a voltage unstable so it is very likely to exceed 5v which is the maximum voltage for my arduinoin in addition I need to use a fixed voltage, you don’t think that the reguateur voltage is a good idea ??

The Vin pin can take 7 - 12 volts, and has an onboard regulator to regulate it to 5. It is unclear that you need an addtional regulator.

Ingelectro: I send unstable voltage...

How "unstable"? You can't expect a reply without any information.

Pololu sells some step up/step down regulators that will accept voltages over a wide input range above and below 5 V, and produce a steady 5 V. http://www.pololu.com/category/133/step-up-step-down-voltage-regulators