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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?

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    The loads of a supply are typically connected in parallel, not in series. Read Series and Parallel Circuits. – Edgar Bonet 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. – Gerben Sep 27 '20 at 18:35
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A power supply a 9V battery is not. Since you are using batteries the L293D is a very poor choice for a driver, it uses silicon transistors which I believe are in a darlington configuration which will cause a voltage drop of from 1.4 to 2.8 volt on the motor. The 4 (or more) AA batteries will work but use a MOSFET bridge. You can always use a small SEPIC (Buck/Boost) converter to power it, that will keep the voltage constant until the batteries are exhausted. Set it to about 9V and power the arduino via the VIN input for more filtering. You will need a way of measuring voltage. You will lose less power with the converter then you are losing in your current driver.

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