LabJack Write Task
Learn how to create a write task for Labjack hardware.
A write task is used for sending commands to your digital outputs and writing analog signals out from your LabJack. In this guide, we’ll walk you through the steps to create a write task in Synnax.
Prerequisites
Before configuring the task, you’ll need to have connected and configured a LabJack device and created the relevant channels in Synnax. Check out the Configure Device guide for more information.
A Short Primer on Tasks
Tasks are the primary method for communicating with hardware devices in Synnax. Tasks can be used for both control and data acquisition purposes. In the context of the LabJack driver, a write task defines a background process that writes data to the analog or digital outputs on a particular LabJack device.
A write task can be started, stopped, and re-configured at any time. Synnax permanently stores the configuration of each task, so it’s easy to set up multiple tasks for different purposes.
How Commands Work in Synnax
Commands in Synnax require two types of channels: a command channel and state channel.
Command channels signal a task to set the value of a digital output. To set a digital
output to high, you would write a 1 to the command channel. To set it to low, you
would write a 0.
A command channel for a digital output might be my_temp_card_do_0_1_cmd, where
my_temp_card is the device identifier, do_0_1 is the port and line of the digital
output, and _cmd indicates that it’s a command channel.
Command channels also have an associated index channel that stores the timestamps at
which commands were sent. This channel is suffixed with _cmd_time. For the command
channel my_temp_card_do_0_1_cmd, the index channel would be
my_temp_card_do_0_1_cmd_time.
State channels represent the current state of the digital output. When you send a command, the corresponding digital write task will process the command and update the value in the state channel.
State channels are typically suffixed with _state. A state channel maintains the same
format as its corresponding command channel, but suffixed with _state instead of
_cmd.
As an example, to configure a valve in a schematic to
write to a digital output, you would set the command field to the command channel of
the digital output and the state field to the state channel of the digital output.
Clicking the valve would send a command to the digital output, and the valve would turn
solid or transparent based on the state channel.
Using two channels provides a guarantee that a particular command was acknowledged by a running task.
Open the Task Configuration Dialog
From the Resources Toolbar
To create a write task from the resources toolbar, open the Synnax Console and click on the resources () toolbar in the left sidebar. Find the device you’d like to create the task for, right-click on it, and select “Create Write Task”.
From the Command Palette
To create a write task from the command palette, open the Synnax Console and click on
the Command Palette at the top. You can also open this palette with
Ctrl+Shift+P on Windows/Linux and Cmd+Shift+P on macOS.
In command mode (enabled when the first character in the input is “>”), type “LabJack”.
You’ll see an option called “Create a LabJack Write Task”. Select this option to
open the read task configuration dialog.
From The Layout Selector
To create a write task from the layout selector, click on the Add () button in the top right corner and select “LabJack Write Task”.
Configure the Task
Step 1 Select your LabJack Device
The first step is to select the Labjack device you’d like to write to the outputs of. Use the dropdown menu in the top left corner to do so.
Step 2 Add Channels to the Task
Next, you’ll need to add the channels you’d like to write to. Click the Add () button in the channels section. Then, click on the new channel in the list to configure it.
You’ll need to select an output port to write to. You’ll also need to select the command channel the task will listen to, and the state channel that will be updated when the command is processed.
Step 3 Configure the State Update Rate
The state update rate determines how often the state channels in the task are updated. Set the rate higher in scenarios that require quick response times.
Start the Task
Once you’ve added all of the channels you need and have configured sampling rates, hit the “Configure” button. If there are no errors, Synnax will acknowledge the configured task and enable the Play () button in the dialog. Click this button to start the task.
Starting and stopping a task does not re-apply the task configuration. If you’ve made changes to the configuration, you’ll need to re-configure the task by hitting the “Configure” button.