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Transistor Help

e14 Contributor

I'v bin working on an arduino powered rc robot, I'v pulled out the old chip and my arduino is plugged into the motor via transistor and pins, the transistor has an external supply and grounds are connected but, all it does is make a weird buzzing in the motor. the buzz does change tone witch makes me think the arduino is doing something. I will put my code and pic of wiring below. please help.

 

     1k resistor and the transistors # is 2N 2904 331 and the power supply is a 6v rechargeable that came with the car

image

 

int motorPin = 9;

 

 

void setup(){

  (motorPin, OUTPUT);

}

void loop(){

  analogWrite(motorPin, 255);

  delay(1000);

  analogWrite(motorPin, 200);

  delay(1000);

  analogWrite(motorPin, 100);

  delay(1000);

  analogWrite(motorPin, 0);

  delay(1000);

}

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  • Hi Kyle,

    Was it working before?

    Not enough info to really analyze but here is some speculation...

    The 2N2904 is a PNP transistor, so it is likely providing more than 5 volts to your arduino output pin, (but I'm just guessing how it is connected). This is not a great situation, but assuming it didn't blow your arduino...

    If the 1K resistor is between the transistor base and the arduino, this is good to limit arduino current to 5 or 6 mA, but may not permit much current out of the transistor, which has a current gain of about 20. By my calculation it would supply only about 100 mA to the motor. (The transistor is rated at about 500 mA) Many performance motors in these small cars can take many amps - some over 40 amps. If you have a low impedance motor, 100 mA may indeed just make it buzz a bit. If this is the case, you would need a much higher current transistor with much higher current gain. (Using a Darlington configuration would likely help, but the output transistor still needs to be large enough and may need a heatsink.

    Doug

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  • Hi Kyle,

    Was it working before?

    Not enough info to really analyze but here is some speculation...

    The 2N2904 is a PNP transistor, so it is likely providing more than 5 volts to your arduino output pin, (but I'm just guessing how it is connected). This is not a great situation, but assuming it didn't blow your arduino...

    If the 1K resistor is between the transistor base and the arduino, this is good to limit arduino current to 5 or 6 mA, but may not permit much current out of the transistor, which has a current gain of about 20. By my calculation it would supply only about 100 mA to the motor. (The transistor is rated at about 500 mA) Many performance motors in these small cars can take many amps - some over 40 amps. If you have a low impedance motor, 100 mA may indeed just make it buzz a bit. If this is the case, you would need a much higher current transistor with much higher current gain. (Using a Darlington configuration would likely help, but the output transistor still needs to be large enough and may need a heatsink.

    Doug

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