kind of transistor for small dc motor

Hi everybody,

first of all, thank you for this great forum which help me to intro to Arduino.

I want to control a small dc motor with a pin from Arduino. I saw a schematic here http://www.hispavila.com/3ds/atmega/motorescc_files/motorcc_tr.gif and I am wondering how can I know the kind of the transistor for this power (5v)? Also, why do I have to put a resistor in front of the Arduino's pin? It is protection? I know they are electronic questions.

Thanks in advance!

If you think about it, the voltage has very little to do with the choice of transistor. Imagine you'd said "12V motor" - it could be a model railway loco...or a diesel engine starter motor. Both could be termed "small".

The diagram suggests an NPN, but you need to know the stall current of the motor.

The resistor is there as a current-limiter.

Sorry, I didnt write details for the motor. Is a 3v motor so I think I dont need a transistor, do you agree?

Link specs of the motor.

As AWOL said volts don't matter. It's the current draw of the motor.

Mine is the first one: http://www.bitsbox.co.uk/motors.html

As I can see, I need 450 mA to feed the motor and Arduino´s pin only provide 40 mA. Right?

Something like a TIP120? I think even a 2n2222 would work. Quite a lot of current for a small motor - no stall current posted.

I am interested on how do you know is TIP120? where do you look for? what is the way to know a specific transistor? thanks for your answers

I think the TIP120 may be overkill, but is a good solid common transistor to use for stuff like this. It is a Darlington (actully it is two transistors in one package), so has high gain, and is good for up to about 5 amps (IIRC).

The 2n2222 is good for up to about 1 amp, but the gain is only about 1/3rd that of the TIP120.

but the motor only need 450 mA and you speak about 5 A

Yes. That’s right 450mA < 5A

I have a bag full of them, so I use them a lot.

Thank you for explain it me so patiently. I will try with one of them ;-)