We are building a robot using 4 servos on a Arduino Uno board. I plan to hook it to a 9v battery when we show it. I read another thread saying he used 9v battery and it ruined the board? I am scared. Please help me on here--if I use 9v battery to power my uno board, and plug in all 4 servos into 5v power pin, would it burn my board or it will be ok? How do you calculate how much power you need for the whole thing? Thanks.
Little square 9V battery? They only have 300mAH or so of capacity, will not last long.
On board regulator is only good for 800mA max.
You are better off to connect the servos in parallel with the board with their own regulator, connecting all the grounds together.
You need to check the current rating (mA) on the servos. Your total current draw is the sum of the servo currents plus the Arduino current. That will tell you about how long your battery will last, and if you can use the on-board regulator.
I read another thread saying he used 9v battery and it ruined the board? I am scared.
If you want to be safe, do what CrossRoads says and don't power the servos from the Arduino...[/b] Just sent the control pluse from the Arduino to the servo. It's best not to power anything other than a few LEDs from the Arduino's voltage regulator and if you need to power more stuff (like motors), you'll need to make some calculations to see if it's possible. I would guess that when you make the calculations, you'll find that the 4 servos are over-stressing the Arduino's regulator.
The more current you draw through the Arduino's voltage regulator, the hotter it gets. And the more voltage you "drop" across the regulator, the hotter it gets. (Power is calculated as Voltage x Current, and the power is dissipated as heat.)
Of course, any power wasted/dissipated in the regulator has to come from the power supply or battery. This shortens battery life. With 9V into a linear regulator and 5V used in your circuit, you are wasting almost as much power as you are using in the Arduino & servo.
Switching regulators are more complicated, but they can be almost 100% efficient. Under normal conditions, you'll get more current-out of a switching regulator than goes-in. (It's not more than 100% efficient and the voltage-out is less than the voltage going-in, which is the whole point of a voltage regulator.)
The energy in a battery is related to it's milliamp-hour rating. A [u]9V Energizer battery[/u] is rated at about 500mAh. So at 100mA, it can go for about 5 hours.* At 500mA, the milliamp-hour rating is reduced, and you can go less than one hour.
- IIRC A battery is considered "good" down to about 80% of it's full-charge voltage. So, you'd be at about 7V and the battery could power the Arduino for awhile longer.
charboing:
We are building a robot using 4 servos on a Arduino Uno board. I plan to hook it to a 9v battery when we show it. I read another thread saying he used 9v battery and it ruined the board? I am scared. Please help me on here--if I use 9v battery to power my uno board, and plug in all 4 servos into 5v power pin, would it burn my board or it will be ok? How do you calculate how much power you need for the whole thing? Thanks.
Servos are typically designed to be powered by 5V-6V. Supplying 9V has a definite risk of frying the electronics.
A typical PP3 9V battery has a maximum capacity of a few hundred mAh. A typical hobby servo is generally reckoned to need up to an Amp (depending on the forces it's being asked to generate) so could flatten a PP3 very quickly. However a PP3 also has a very low output current, and may not even be enough to operate the servo motor properly.
By far a better power source is a set of four AA batteries.