Property Links are a very useful feature of Helm that simplifies the business of connecting controls to device parameters. The beauty of Property Links is that they can work both ways automatically updating the status displayed and letting you control the parameter at the same time. But enough theory, let’s look at some practical examples:
Linking a fader to audio gain
Here we have a very simple panel with a fader controlling an audio gain value on a Lynx frame synchroniser card. To demonstrate the property link we’ve also linked a text label to the same property to show the value changing as we change the fader position. So let’s run the panel and see what happens.
Lower the gain
We pull the fader down a bit and the gain reduces. You can see this in the text label. The reason I’ve opened the window a bit is to show you the software running behind Helm. Here we’re looking directly at the card using the Lynx Apollo control software and you can see that the new gain value is also reflected there.
Raise the gain
This time I’ve set the gain to -5dB using the Lynx software to show that control and status work both ways.
Read-only and Read-Write Properties
Some properties can be modified / controlled by Helm and some simply reflect the status of the device or the signals it receives. Helm handles this intelligently. When you are setting up a property link for an active control like a fader only read-write properties are displayed by default. Lets look in more detail at our fader. If we click on the ellipsis (1) to open the Property Link dialog (2), at first we see only the properties which the fader can actually control. But we also have the option to Show Read-Only properties (3). If we check this we get the full list including read-only properties.
If you link a fader to a read-only property it becomes a passive indicator of the current device status and it gets updated according to the device polling interval.
Showing status using text labels
Here we’re changing the Property Link of our text label to reflect the Status Color of the Lynx card. Because Text Labels don’t control device parameters, Show Read-Only properties is checked and all properties are available. Once the link is set the text shows the current card status – in this case green.
You can use Property Links with most Helm controls. The exceptions are those where it really does not make sense. For example Text Boxes: allowing free form text input to a device parameter is in effect testing the data validation built in to the device. Using a dropdown to put pre-defined values is a lot safer.
You could do this all in Helm script i.e. setting the current value of the control to the current device status and updating the device parameter to the current control value whenever the control is moved by the user. But it would take far longer to set up. Property links save you a lot of scripting time by doing the obvious.