Why do Arduino needs 7V - 12V ?

The uC of Arduino Mega needs only 5V. When I plug Servos and Arduino to 6V Power Supply, it always turn off and on because Arduino don’t have enough power. I see in description Arduino needs 7V - 12V, but why is this so? Why can’t this voltage regulator convert 6V to 5V ?

And what is the solution? Because it should be power supplied from only one 6V source.

why is this so?

Old, inefficient design.

Use a different regulator and apply the regulator output to the Vcc (5V) pin. This one will work on a large range of input voltages, above and below 5V.

A linear regulator needs about 1.5V above the voltage it is trying to regulate to. This is known as the drop out voltage and is the consequence of the design using bipolar transistors and how they work. You can get “low dropout” regulators where this voltage can be in the order of 1 to 0.5V, but they are more expensive and require more expensive capacitors to surround them. So it is a matter of need versus cost on the Arduino board.

Not many people need that feature but every one would have to pay for it.

When I plug Servos and Arduino to 6V Power Supply, it always turn off and on because Arduino don't have enough power

Nothing to do with the regulator or smaller supply voltage, it is the interference from the servos. You need some solid decoupling circuits involving inductors and capacitors to isolate the servo supply from the Arduino. See the last schematic on this page De-coupling

Grumpy_Mike:
A linear regulator needs about 1.5V above the voltage it is trying to regulate to. This is known as the drop out voltage and is the consequence of the design using bipolar transistors and how they work. You can get “low dropout” regulators where this voltage can be in the order of 1 to 0.5V, but they are more expensive and require more expensive capacitors to surround them. So it is a matter of need versus cost on the Arduino board.

Not many people need that feature but every one would have to pay for it.
Nothing to do with the regulator or smaller supply voltage, it is the interference from the servos. You need some solid decoupling circuits involving inductors and capacitors to isolate the servo supply from the Arduino. See the last schematic on this page De-coupling

Okay, thank you. I am using 16 servos. 8x mg996r and 8x 9g servos. Which inductor should I buy? I often order from aliexpress or ebay. I think I also have to use a bigger capacitor ? Maybe I could use 2200 uF from old mainboards?

I am using Arduino Mega Sensor Shield to connect it to servos.

Eight mg996r have a combined stall (startup/move) current of 20Amp.
Add 5-6Amp to that for the eight 9g servos, so you need a 5-6volt/25Amp supply for the servos alone.
Not possible to route that sort of current through a sensor shield.
Leo..

well i can solder extra conductor track on the back of sensor shield

well i can solder extra conductor track on the back of sensor shield

You certainly can, but it may just vaporize.

you need a 5-6volt/25Amp supply for the servos alone

forgoden:
Because it should be power supplied from only one 6V source.

That is false.
You can have a separate power supply on each servo if needed.
Just make sure to run a ground wire for each to the arduino.

well i can solder extra conductor track on the back of sensor shield

The connectors may only be rated for low current as well. The female headers on the Arduino are only rated for 1A.

forgoden:
well i can solder extra conductor track on the back of sensor shield

“The bitterness of poor quality remains long after the sweetness of low price is forgotten” – Benjamin Franklin

"A slow and painful learning curve leads to well ingrained habits" -- somebody.

Hi,

Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?
Including the power supplies and servos.

Thanks... Tom.. :slight_smile: