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schematic

simulate this circuit – Schematic created using CircuitLab

I have a wire connected to the base of the transistor that goes to the PWM pin 9 on the Arduino Uno.

On the collector of the transistor I have a 7.5v battery and the emmitter is connected to a motor which then connects to ground.

On the emitter of the transistor I am only seeing 2v, why is this? Is there anything I can do to change this?

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    \$\begingroup\$ Edit your question and use the schematic tool. \$\endgroup\$ – Ignacio Vazquez-Abrams May 16 '14 at 2:58
  • \$\begingroup\$ Couldn't find the motor icon... \$\endgroup\$ – Jister13 May 16 '14 at 3:06
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You've set up the NPN transistor as a high-side driver, but you aren't feeding the base a high enough voltage for it to be effective. Move the motor to between the collector and the positive terminal of the battery in order to turn the transistor into a low-side driver.

Also, put a resistor between the base and the Arduino so that you don't try to pull the positive supply down to 0.7V (between 820 ohm and 1.2 kohm should do), as well as a diode across the motor so that you don't blow up the transistor.

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ So I should have the emitter go to the negative of the battery then? \$\endgroup\$ – Jister13 May 16 '14 at 3:19
  • \$\begingroup\$ Yes, as well as ground of the Arduino. \$\endgroup\$ – Ignacio Vazquez-Abrams May 16 '14 at 3:22
  • \$\begingroup\$ Now it is working, but it is reversed... High power to it means motor goes on... \$\endgroup\$ – Jister13 May 16 '14 at 3:23
  • \$\begingroup\$ Modified the answer a bit, with a very important change. \$\endgroup\$ – Ignacio Vazquez-Abrams May 16 '14 at 3:28
  • \$\begingroup\$ What was the very important change? The diode? Also, why is it that my motor doesn't start up when I give it power. It needs a push to get started... (This was a current problem, fixed now) \$\endgroup\$ – Jister13 May 16 '14 at 3:28
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It's your circuit look like this?! If not, try make it so.

enter image description here

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