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143 lines
5.4 KiB
Markdown
143 lines
5.4 KiB
Markdown
---
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title: Patch Nodes
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---
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Patch Nodes
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===========
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What you see on the tab in the main workspace is called a *patch*. A XOD patch
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corresponds to a single source file or module in other programming languages.
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Until now, you’ve created single-patch programs and the patch was
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automatically named `main`. Creating a whole project in a single patch would
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become messy once the number of nodes and links passed some limit. It is often
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a good idea to split complex patches into several simpler patches that are
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easier to understand and edit.
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Furthermore, you can reuse patches several times in your project with slightly
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different parameters, thus avoiding node duplication.
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When you use one patch as a node in other patches it is called a *patch node*.
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In this chapter, we’re going to build a simple watering station for two plants.
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The idea is to water a plant if its soil became too dry and constantly show the
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current soil measurements on an LCD screen.
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Single plant station on a single patch
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--------------------------------------
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To start, let's build a device that will work with a single plant. We’ll use
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a single patch called `main`, as in previous chapters.
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Create a new project called `water-station` and wire up your circuit:
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Now make the following patch to control the device:
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Be sure to set port values properly for all hardware nodes.
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You may have noticed it is very similar to the previously implemented smart
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light project. We've only changed the sensor and the actuator. The moisture
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sensor replaced the light sensor, and the pump replaced the LED.
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Upload the program to your board and test the device. Put the sensor into a
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glass of water and take it out. See how the pump reacts. Observe the text
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shown on the LCD.
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Let’s improve the program a bit by adding pretty formatting to the messages
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so that instead of `"0.42"`, the LCD would show something like `"Cactus: 42%"`.
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We achieve this by adding two nodes. First, a `to-percent` node will convert a
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number from the sensor to a string like `"42%"`. Second, the `concat` node will
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concatenate the constant prefix `"Cactus: "` with the percent string:
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<div class="ui segment">
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<p>
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<span class="ui ribbon label">Hint</span>
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You can click the help button
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<img src="./guide.svg" style="vertical-align: middle" height="16"/>
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in Inspector or Project Browser next to a node name to open node’s reference
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and learn what the node does.
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</p>
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</div>
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Extracting plant logic to a separate patch
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------------------------------------------
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So far, so good. Now consider that we want to extend the device to handle two
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plants at once. We have another sensor, yet another relay, and a pump. What we
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want to share is the LCD. Each plant’s message should be shown on its own line.
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The very staightforward way to do it would be to duplicate most of nodes
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related to reading and comparing data, and formatting the result. But it would
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quickly become unmanagable and error prone. Changes in one place would always
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require manually mirroring those changes in other places.
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Patch nodes to the rescue. What do the different plants have in common? And
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what is different? The logic is common, but the name of the plant and its
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watering threshold value differ. The ports used to connect the sensor and the
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relay are also different. So these things need to be provided as parameters to
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our patch.
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What might the patch output to the outside world? It could be a status message
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string.
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Create a new patch with File → New Patch, and name it `plant`. Look at
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Project Browser. You’ll see that a `plant` patch has appeared next to our
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`main`.
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First of all, we’re going to define its inputs and outputs. Expand
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`xod/patch-nodes` in Project Browser and notice nodes with names like
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`input-xxx` and `output-xxx`. They are called *terminals*, and define the
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patch's input and output pins. Place a few inputs and outputs according to what
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we’ve planned to parametrize:
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Now give the terminal nodes informative labels so we can remember which one
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means what:
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Switch back to the `main` patch and try to add two nodes of our newly created
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type `plant`:
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We’re going to use these two nodes to manage plants and move the existing
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logic to the shared `plant` patch. Let’s do it.
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<div class="ui segment">
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<p><span class="ui ribbon label">XOD T0D0</span>
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Currently there is no cut/copy/paste in XOD. Yes, that’s a pain. We’ll
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implement it in future versions. If you would like to give the feature more
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priority, we welcome you to <a href="//forum.xod.io">share your opinion on our
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forum</a>.</p>
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</div>
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Here is the final `main` patch:
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And the `plant` patch:
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Wire up the circuit:
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Set parameters for your plants with Inspector. Then upload the program and see
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how both plants are served simultaneously with a single patch.
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What’s next
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-----------
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Our quick tutorial is almost complete. The last thing to learn is what you can
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do to build arbitrary projects with arbitrary hardware. See the [Complex
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Projects](../complex-projects/) chapter to learn more.
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