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Learning BeagleBone Python Programming by Alexander Hiam

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Driving higher currents from GPIO pins

We just calculated that a 68 Ω resistor will give us the maximum forward current from a 3.3 V supply, but when we hooked up the LED to the 3.3 V GPIO pin earlier, we used a 330 Ω resistor. This is because the GPIO pins of BeagleBone's processor are only rated to source a maximum current of 4-6 mA. Using a 330 Ω resistor gives 1.3 V / 330 Ω = 3.9 mA.

There are a few ways we can source more current than the 4-6 mA maximum of the GPIO pins; one simple way is to use an NPN Bipolar Junction Transistor (BJT).

For this circuit, you will need:

  • Breadboard
  • 1x 5 mm LED
  • 1x 4.7 kΩ resistor
  • 1x 68 Ω resistor
  • 1x 2N3904 NPN transistor
  • Jumper wires

Wire it up on your breadboard as shown here:

Note

If you have a resistor kit like the ...

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