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131 lines
5.1 KiB
Markdown
131 lines
5.1 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 in a tab of main work area is called a *patch*. In other
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programming languages a XOD patch corresponds to a single source file or
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module.
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Until now you’ve created single-patch programs and the patch was given name
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`main` automatically for you. Creating a whole project on a single patch would
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become messy once number of nodes and links will pass some limit. In many cases
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it is a good idea to split complex patches into several that are easier to
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understand and change.
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Furthermore, you can reuse a patch several times in your project with slightly
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different parameters and in such way avoid nodes duplication.
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The mechanism which lets you use one patches as nodes on other patches is
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called *patch nodes*.
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In this chapter we’re going to build simple watering station for two plants.
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The idea is to water a plat if it’s soil became too dry and constantly show current
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soil measurements on text LCD screen.
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Single plant station on a single patch
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--------------------------------------
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To start lets build a device that will work with a single plant. We’ll use single
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patch `main` as in previous chapters.
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Create new project `water-station` and wire up your circuit:
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Now make a following patch to control the device:
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Make sure to properly set port values for all hardware nodes.
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You may noticed it is very similar to previously implemented smart light project.
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All things we’ve changed is the sensor and the actuator. Moisture sensor replaced
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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 glass
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of water and take it out. See how the relay reacts. Observe the text shown on LCD.
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Let’s improve the program a bit and add pretty formatting to the messages. So that
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instead of `"0.42"` the LCD would show something like `"Cactus: 42%"`. We achieve
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this by adding two nodes. First one `to-percent` would convert number from sensor
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to a string like `"42%"`. Second one `concat` would concatenate a constant prefix
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`"Cactus: "` with the percent string:
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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 we want to extend the device to handle two plants
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at once. We have another sensor, yet another relay, and pump. What we want to
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share is 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 duplicate most of nodes related to
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reading data, comparing it and formatting the result. But it would quickly became
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unmanagable and error prone. Changes in one place would always require mirroring
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the changes in other places by hand.
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Patch nodes to the rescue. What do we have in common between different plants and
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what differs? The logic is common, but the name of the plant, its watering threshold
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value differs. Ports used to connect the sensor and the relay differs too. So
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these things should be provided as parameters to our patch.
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What the patch could output to the outside world? It could be a status message
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string and a pulse that denotes that update is completed.
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Create new patch with File → New Patch and name it `plant`. Look at Project Browser
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you’ll see that `plant` patch has appeared next to our `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 patch
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input and output pins. Place few inputs and outputs according to what we’ve
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planned to parametrize:
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Now give the terminal nodes informative labels so that we can remember which one means
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what:
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Switch back to the `main` patch. And try to add two nodes of our newly created type
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`plant`:
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We’re going to use these two nodes to manage plants and move existing logic to the
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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 implement it
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in future versions. If you would like to give the feature more priority we welcome you to
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<a href="//forum.xod.io">share your opinion on our forum</a>.</p>
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</div>
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Here is 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 how
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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 completed. The last thing to learn is what you can do
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to build arbitrary projects with arbitrary hardware.
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See [Complex Projects](../complex-projects/) chapter to know more.
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