If scratch is “Programming for kids”, then NodeRED is “programming for adults that love Scratch”. I’d venture to say that once you learn the NodeRED way, you will kiss goodbye ever wanting to write Python again!
To begin, start NodeRED from Pi by selecting Programming->NodeRED from the top menu. Once it is done, open Chromium browser and type http://localhost:1880 . Let’s write a NodeRED program.
A NodeRED program is called a flow. Here is an example of a flow.
You can run a number of flows at the same time. You export and import flows that others have written or that you want to share with others.
In the example above, we have dragged and dropped the Inject and Debug onto the design area and connected them together by clicking on the white boxes on the nodes.
Here is how the Inject node is configured.
The inject node is useful for initiating the message flow between nodes.
Here is how the Debug node is configured.
Once the flow is configured, we are to deploy and run our first flow in NodeRED.
When you click Deploy at the top, nothing happens. To get you program to run, click on the left-side of the Inject node, which triggers a message that is sent to the next node. You should see the output on the Debug tab to the right.
To understand what the connection between the two nodes mean, we have to look a the concept of message passing.
Nodes generally execute when they receive an incoming message (ie. the node preceding it sends it something). You usually use the inject node to start the ball rolling, but there are others such as serial,mqtt that already run when you hit the Deploy button.
To understand what is really happening, let’s modify our example slightly.
Let’s complicate a bit more.
We will start with a detour and write the program in python first.
Now for the NodeRED version.
Here we introduce three new nodes: function, http request and template.