Electronic – arduino – 5V 4A power supply for simple circuit

Here is a possible DIY solution for solar powered Arduino system: https://www.cooking-hacks.com/documentation/tutorials/arduino-solar/

The principle is pretty basic. A rechargable battery sufficient to power the system for 18-24 hours, a panel of photo-voltaic cells (solar battery), and something to manage charging the battery from the solar panel.

There are many possible solutions, from full custom assembled from various parts, to a turn-key complete system in a box. It would be good to have a basic meter if you are playing around with electronic stuff. You could measure the actual current used by your Arduino, and calculate the size of battery you need for the expected solar radiation in your location. You would need a larger battery farther toward the polar regions than you would need near the equator, etc.

Although I haven't used the SG90 servo, most RC servos want to see about 6 Vdc with significant current capability.

Even though the servo might be lightly loaded, you still have to get the motor spinning everytime the servo begins to move. The motor stall current can be significant - anywhere from several hundred mA all the way to to several Amps.

Because the servo is lightly loaded, you can probably get away with a really simple linear regulator. The simplest such regulator is a simple Zener diode followed by a series-pass current-boost transistor.

Something that I have used in the past is as follows:

^{simulate this circuit – Schematic created using CircuitLab}

This is good for up to 1 Amp or more for brief surges and is perfectly adequate for powering a RC servo. Note that the regulation is fairly lousy but the servo won't mind.

[Edit]

Someone commented that this servo doesn't want to see more than 5V. This is an easy fix: simply change the Zener diode to a 6.2V part instead of 7.5V. That would be 1N4735 or 1N5234. This will provide a nominal 5V output.