Problem connecting motor to arduino

Question

I am trying to connect a DC motor to an arduino.

When I set it up like in the first image below, it works and the motor rotates. However, when I set it up in the second image it does not work, am I missing something really obvious? Any help would be great..

Code I am using for image 2:

int pinMe = 11; // the pin we will use as output

void setup() {
  // put your setup code here, to run once:
  pinMode(pinMe,OUTPUT);
  digitalWrite(pinMe,HIGH);
}

void loop() {
  // put your main code here, to run repeatedly:
  digitalWrite(pinMe,HIGH);


}

Also when I check the voltage in the second image from pin 11 to ground it reads 4.98V but when I add the two wires from the motor to the bread board (in image 2) the voltage reads 0.14V

Answer 1

You have connected your motor directly to an OUTPUT pin of a microcontroller rated at 20mA output current, bad idea.

Firstly it will destroy your micro, the reason you see such a low voltage when you connect the motor to a output is because the PTC is saving it or as @gbulmer mentioned that you may have fried the internal driving circuitry of the AVR(the main chip on the arduino), you should confirm this with a LED and resistor.

The load is inductive also this will destroy your arduino.

You should have the following setup, using a transistor, current limiting resistor and a flyback diode:

http://www.electronics-tutorials.ws/io/io32.gif?74587b

Answer 2

Your problem is very simple and common. If you read the specifications for Arduino Uno you will find that the max current per I/O pin is only 40mA.

The motor you are using will need much higher current(if not constant then pulsating), without the current your motor fails to start and hence you are not able to get the motor to rotate.

When you connected directly to 5V, you got enough current as it was from the input which you have given to the Arduino.

A simple solution to your problem is to use a motor driver IC like L293D or if you want you can also use a transistor to drive the motors.