I'm doing some learning with Arduino, and to test some concepts I've put a very simple circuit with a car toy DC motor.
I don't have any specifications for the motor, and don't have a clue on how to get them.
First the circuit (sorry for the atrocious ASCII):
9V +---------|---------|-DC motor--|-o
Sensor C (collector)
| ....Arduino magic.. B (base)
E ----- GND
I'm using a transistor (2n3904) as a switch to turn on the motor. The base is connected to a digital pin that responds to a light sensor.
Both the Arduino and the motor are powered with the same 9V battery. When I shine a light on the sensor, the motor spins if there is almost no load (wheels off the table), but as soon as I put the car on the table, it stops. My guess is the 9V battery is not enough for both the Arduino and the motor, but I've tried this with external supply for the Arduino (serial cable) and got the same result.
When I feed the 9V directly to the motor, it works. I know there is a V loss on the transistor (around 0,3?), but I don't think this should be trouble...