Book Image

Learning Beaglebone Python Programming

Book Image

Learning Beaglebone Python Programming

Overview of this book

Table of Contents (19 chapters)

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:


If you have a resistor kit like the one from SparkFun ( you might not have a 68 Ω resistor handy. If this is the case, you can use one 220 Ω resistor in parallel with one 100 Ω resistor for a combined resistance of 68.75 Ω.

Let's take a quick look...