# How to calculating requirements of power supply for a project

I am starting with electronics and been working with Arduino for some time now. I did some basic LED and servo motor project and was hoping to jump into making an obstacle-avoidance car. I used 4 AA batteries to make it, but the voltage was too low, as the motors were not moving. Then I knew about the volt requirements and all that. I also tried with a 9v alkaline battery, but it didn't help much.

Here are the electrical parts I used:

1. Arduino
2. Ultrasonic sensor
3. 4 toy motor
4. 1 hobby servo motor
5. Motor driver shield L293D
6. Battery

These are the operating voltages that I know of:

1. Arduino = 7 to 12 v
2. Hobby servo motor = 3.0V~ 7.2V
3. Toy motor = 3v ~ 12v dc; has a No load current 40 - 80 mA

Because AA batteries are of 1.5v and are in series, it has 6v, and I am assuming that was the reason it was not working as expected. What I am confused about is, how do I choose a battery or power supply to be specific.

Please forgive me for asking such a noob question. Since 1 Arduino + 4 toy motor + 1 hobby servo motor = 7v + 4 x 12v + 7v = 62 v, but I checked and I couldn't find battery that is above 15v. I surely don't understand how to pick a power supply. Could you please help me out on how to calculate and choose the right battery/power supply? Also, what to look for if for example, I want to run it for a minimum of 10 minutes?

• The loads of a supply are typically connected in parallel, not in series. Read Series and Parallel Circuits. Sep 27 '20 at 16:27
• 9V batteries can hardly handle any current, so that's probably why that didn't work for you. I'd add more AA batteries in series. Using 6 would give you 6-9V (6V when empty, 9V when full). 8 would give you 8-12V. In that case you'd have to run the servo from the regulated 5V on the Arduino, as to not exceed its rated voltage. Sep 27 '20 at 18:35