I read from the technical specifics page for the arduino boards that if the supplied voltage is less than 7v, it may supply less than 5v
but what if I connect 3 micro/mini servos (and nothing else), would it be able to reliably supply 5v ?
No, even those tiny motors can pull some current which the Arduino can't deliver if you power it via Vin (thus the regulator).
And that 7V limit has nothing to do with what you connect. If you drop below 7V you don't get 5V from the Arduino. If you want to power it with 5V just use the USB. Easy way, grab a charger. A charger (of 1A or bigger) can also power the micro servo's 
thanks sept
so even the smaller arduino nano, micro etc have voltage/current protection for their size if I choose a 7-9v power supply right?
Almost all Arduinos have voltage regulators which can power the Arduino from a wide range of input voltages. 7-16V is likely to work for most Arduinos.
The problem is if you're trying to power something else, like a servo. The Arduino's onboard regulator can't supply enough current for a servo. Even an LCD display can overheat the regulator under some conditions.
If you told us exactly which servo (link to a datasheet) then we might have a better answer for you.
Most don't have voltage or current protection. A normal Uno has current protection but that does not take in account the overheating of the regulator. And I've never seen one with voltage protection, only most boards have a regulator to accept a voltage range.
morgan
I've yet to select any servos but I do have a shortlist, eg futaba s9650, 3016 as the project is still in the conception stage. thanks
sept
how would I know if i need voltage protection? power source would be a battery.
MorganS:
Almost all Arduinos have voltage regulators which can power the Arduino from a wide range of input voltages. 7-16V is likely to work for most Arduinos.The problem is if you're trying to power something else, like a servo. The Arduino's onboard regulator can't supply enough current for a servo. Even an LCD display can overheat the regulator under some conditions.
If you told us exactly which servo (link to a datasheet) then we might have a better answer for you.
I personally do not go higher than 12V on Vin, this is due to the power dissipation in the 5V regulator onboard the controller.
Servos tend to appear as surge loads due to the characteristic of their operation.
A combination of low current rating regulator, thin on board conductors and very little in the way of filter capacitance, means the on board 5V, when supplied by the Vin, will cause the controller to reset when a servo wants to move.
Tom...
I use one of these.
or
To supply servos.
I've decided to use a linear voltage regulator instead and independently power the servos and arduino
if I use a 7806, would the 6v output be ok for the arduino since they recommend 7-9v input?
also, I am quite confused over the choice of capacitors to use since some diagrams show 100uf, some 0.33uf etc
Input will be either 3s lipo, 9V or 7.2v (rechargeable batteries).
If I use 7.2v rechargeable batteries, is it going to work since the volt regulator needs a difference of 2.5v between input and output.
Will the use of these input voltages cause the 7806 and/or arduino to run hot?
arduino_x:
Problem with servos is that the specs seldom quote a current figure: some sites do, but it's not common, not that I've seen anyway.You can calculate the current from what they give you though. They tell you the torque and the rotation speed so you can get the power since P=Tw and then current from i=P/V.
I found this calculator.
this is fine?
Use a 7805 and power the Promini through it's Vcc pin (instead of a 7806 to RAW).
Having separate supplies should help unless the servos take so much current that the LiPo voltage drops too low to be regulated and the 328P resets.
Be sure to connect all grounds together - servo to battery, regulator to battery, promini to battery.
CrossRoads:
Use a 7805 and power the Promini through it's Vcc pin (instead of a 7806 to RAW).Having separate supplies should help unless the servos take so much current that the LiPo voltage drops too low to be regulated and the 328P resets.
Be sure to connect all grounds together - servo to battery, regulator to battery, promini to battery.
what if I need 6v to the servos?
would this be ok?
battery-> 1 wire leads to the board, the other leads to the 7806 then servos - > ground wire joins back?
not sure whether this will be too messy as the 7806 requires some capacitors.
What about electrical noise?
A "6V" servo will probably work fine on a "7.2V" battery. That is a pretty common battery for RC toys and mass-produced toys aren't going to use too many fancy voltage regulators. However I've not blown up enough servos myself to tell you if it "definitely will". I can only say "probably".
Using a 7806 to get 6V on a battery-powered system is a bad idea. Under ideal conditions, you are throwing away 15% of your battery capacity. Probably more in real conditions.
If you really have to convert voltages for high-power devices like servos, then have a look at the range of DC-DC converters available at Pololu.