Tag Archives: GPIO

Beaglebone LESSON 8: Read Button State from Python

In this tutorial we will see how to read digital values from the GPIO pins. We will be doing digital reads, which means we will be limited to “HIGH” or “LOW” readings. This is a 3.3 volt system, so we need to make sure that the “HIGH” applied signal is 3.3 volts.

Our pinout from LESSON 1 shows which pins are suitable for digital reads.

Default Pin Configuration for the Beaglebone Black Rev. C.

It is the green GPIO pins which we can use for digital reads. In this lesson we will demonstrate the digital read technique using a simple two button circuit. In order to complete this lesson, you should go ahead and build this circuit.

Example of Simple Beaglebone Black Button Circuit

Notice we are using Pin 1 on Header P9 as the ground and Pins 11 and 13 on header P9 s the input pins. Also note the pulldown resistors are 1000 Ohm. It is important to use at least this much resistance. If you do not have 1,000 Ohm resistors, using something larger NOT something smaller.

Once you have the circuit set up we are ready to begin programming.

First up, you need to import the GPIO library. If you have the latest version of Debian Wheezy, you should have the library on your system. If you do not have it you will need to update and upgrade your operating system. To load the library, you will use the python command:

We now need to configure out pins P9_11 and P9_13 as inputs. We do this with the command:

Now to read the state of the buttons, we would use the commands:

state1 will be True if the top button is pushed, and False if it is not being pushed. Similarly, state2 will be True when the button is being pushed, and False when it is not being pushed.

We can bring these concepts together to make the following program. Play around with the program and see what all you can make it do.


Beaglebone Black LESSON 5: Blinking LEDs from GPIO Pins

This lesson shows a simple example of how to blink two LEDs from the GPIO pins on the Beaglebone Black. To get going, you will need to hook up the following circuit. (If you have not ordered your Beaglebone Black, you can get one HERE.)

Circuit for Blinking LEDs from Beaglebone Black

Note that the Top LED is connected to Pin “P9_12” and the bottom LED is connected to Pin “P9_11”. We are using 330 ohm current limiting resistors.

The video lesson takes you through several examples of how to blink the LED. Watch the video, and do the examples. Then play around on your own and see what you can make the LEDs do.

Beaglebone Black LESSON 4: Digital Write to the GPIO Pins from Python

In this lesson we show you how to do digital writes to the GPIO pins from python. If you do not already have a Beaglebone Black Rev C, you can order one HERE.

In order to do this lesson, we need to go back and review the pinout diagram from LESSON 1.

Default Pin Configuration for the Beaglebone Black Rev. C.

In Python, we reference pins by first specifying which header we want (P8 or P9) and then which physical Pin. For Example, to specify pin 12 on the left header, we would refer to it as “P9_12”. For digital output, we should use one of the pins above that is shaded green.

To talk to the GPIO pins in Python, we must first import a library. The latest versions of the Beaglebone Black Rev C. are shipping with the library already installed. If you have an earlier version, you need to update to the latest operating system. You can visit the beagleboard.org web site to download the latest operating system. If you get an error when you try and load the library, you know that either you have typed the command in wrong, or you need to update your operating system. In python to import the library you need to include the line:

Once you have imported the library, you then need to setup your pin as an output pin:

Now if you want to set that pin high you can use the command:

To set the pin low you can use the command:

After you are done working with the pin, you should “cleanup” to free the pin up:

These are all the commands you need in order to set the pin “HIGH” or “LOW”. Remember that in the High state, the Beaglebone Black outputs 3.3 Volts.

We can bring things together to make a simple program that will turn the pin on and off in three second intervals. Try and play around yourself with this code. Then try different GPIO pins.