Help attaching a 1.5-3v motor

Forum 2005-2010 (read only) Hardware Interfacing
1

Hey everyone, I am still a noob and need help attaching this motor to the Arduino:

I thought I could use this relay which would switch the motor on and off from a 3v supply (2 AA's):

The motor acts a little funny and I don't know why. It turns on in spurts. I have to be missing something dumb right?

#define RELAY 5

void setup(){
  pinMode(RELAY, OUTPUT); 
}

void loop(){
  digitalWrite(RELAY, HIGH);
  delay(5000);
  digitalWrite(RELAY, LOW);
  delay(5000); 
}
2

It turns on in spurts of five seconds?
Do you have the coil resistance for the relay?

3

It says 250 ohms on the side.

4

Well I put a diode across it and it worked. I don't know why though. Any words of wisdom?

5

Sorry, I automatically assumed you had a diode across the relay - I didn't think to ask.
The relay coil is an inductor (so is the motor), and when it switches off, the magnetic field created when current is flowing through it collapses, and induces a current in the opposite direction. This is very brief but can potentially damage the output pin or transistor switching the relay. The diode absorbs the spike.

6

The diode absorbs the spike.

I thought that the purpose of the diode was to block the spike. May just be a semantic issue, but I think of capacitors as absorbing current and diodes as blocking it.

7

I thought that the purpose of the diode was to block the spike.

No it shorts it out. Normally the diode is not conducting but a reverse voltage makes it conduct and so shorts out the spike.

8

May just be a semantic issue

Would you settle for "dissipates" then? ;D