Category: Classroom

Using NodeRED to program your RaspberryPi for GPIO Control.

The basic installation of Raspian includes NodeRED. However you need to start it to use it.

Connect to your Raspberry Pi using your terminal. Issue the NodeRED startup command:

node-red-start

The first line after the “Start Node-RED” will contain where you need to point your browser. Remember that your Raspberry Pi is a fairly small computer so it might take it a little while to load ( possible minutes ).

The console will update once Node-RED has started, it is ready when you see the final line state “Server s now Running …”

Now we can connect with our browser

Let’s Add Nodes

We will use the Inject Node as the “Button”, Drag one of the Inject nodes to the Flow area:

Double click the node to open the edit panel. From the Payload drop-down select boolean and leave the value as True.

Click Done, and you will see that the Inject node now reads as “true”

To easily find the Raspberry Pi nodes type rpi in the node search tool at the top left. Drag a single rpi gio Output node to the Flow area and drop it near the Inject Node.

Wire the Inject node to the gpio node:

Double click the PIN Node ( rpi gpio ) to enter into edit mode and select Pin 7 and make certain the type is Digital Output.

Add the “Off Switch”

Let’s Drag a Second Inject node onto the Flow area

Double click the Inject to edit

Change it to boolean and set the value to false.

Wire the “false” node to the same pin as the true node.

The final step before you can use either of the buttons is to Deploy the Flow.

Clicking the small blue box next to the “true” inject node will turn the LED on and “false” will turn it off.

To get started with controlling and interfacing electronics with the Raspberry Pi, the easiest and safest way is turning a LED On and Off. It is simple but it works.

Interactively, First

If you have installed Raspian on your Raspberry Pi it comes with Python pre-installed. All you need to do is bring up a terminal and type python <enter> to get to the python console. It looks like this:

The python console let’s you execute code as you go, it is a great way to learn and test small pieces of code.

To control the GPIO pins on the Raspberry Pi we need to add a tool that knows how to control them this is the GPIO Library ( there are others as well ). To add the library we will use the import command. Type the command as show and hit the Enter Key. If done correctly the python console will simply accept it and prompt you for the next line.

>>>import RPi.GPIO as GPIO
>>>

Know that we have the tool we need to tell the python console specifically how to use it. We will be using BOARD mode. This means we will be referring to the PINS as they are physically numbered and laid out. Again you will get no prompt, simply the next line.

>>>import RPi.GPIO as GPIO
>>>GPIO.setmode(GPIO.BOARD)
>>>

The pins are numbered with Odd Pins in one Row and Even pins in the other. The numbering starts from 1 and 2 next to the Power LED. Pin 1 sits near the inside of the board and Pin 2 near the edge. We will wire Pin 6 and Pin 7 to the LED. Pin 6 is GND ( Ground or Negative ) will be wired to the short leg of the LED or the Cathode. Pin 7 will be wired to the Short leg or the Anode.

Next we need to tell python what to do with pin 7. We use the GPIO.setup() command to indicate that the the Pin will be used for output. The GPIO.OUT is used to indicate output.

>>>GPIO.setup(7,GPIO.OUT)
>>>

To turn the LED on we set the pin to True using GPIO.output()

>>>GPIO.output(7,True)
>>>

To turn the LED off we set the pin to False using GPIO.output()

>>>GPIO.output(7,False)
>>>

Let’s make a command file.

To complete this on the command line we will use a program called nano. It is a command line based text editor. For more advance python it can be beneficial to use an IDE

Open the editor by executing the nano command and type all the commands from above into the nano windows

When done press CTRL-O, type in the name ledon.py, press enter the CTRL-X

Test the command, type:

python ledon.py

Our Second Command

copy the ledon.py to ledoff.py, and open the file with nano ledoff.py

Change the True in line 4 to False

Run the command to turn the led off

python ledoff.py

You will notice there is a warning, let’s take care of that.

Using nano add GPIO.cleanup() to the end of each file

You can now turn the LED On and Off from anywhere you can get a terminal on your Raspberry Pi