Example brightness

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This is a guide to the brightness C example project included in the EMAC OE SDK.

This is a simple backlight brightness control. It's written for the EMAC PPC-E7 and SoM-9307 but it will probably run on anything with a backlight. It implements a slider application in GTK+ that directly controls the backlight through its sysfs interface. It has been tested under Xfbdev/Matchbox.

The brightness project builds one executable: brightness.

Opening, Building and Uploading the Project Files

1. Open the C/C++ editing perspective.

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2. Open the project files.

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3. Build the project.

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4. Upload the executables to the target system.

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Usage and Behavior

The brightness C example project creates a GTK+ UI for controlling the backlight brightness. It gives us a slider, a spinner and a textfield.

Hardware Requirements

The brightness C example project is written for the EMAC PPC-E7 and SoM-9307 but it will probably run on anything with a backlight.

Using brightness

From the terminal, first set the DISPLAY variable:

export DISPLAY=:0.0

Then run the brightness C executable:

./brightness

A GTK+ UI appears on the LCD.

Figure 1: brightness ui

Slide the slider, click the spinner arrows or enter a new brightness value (in range [0,255]) to change the LCD backlight value.

Behind the Scenes

The sysclass_get_level() and sysclass_set_level() functions are responsible for retrieving and setting the backlight's brightness value, respectively. These functions demonstrate a method of interfacing with the /sys virtual filesystem to set and retrieve values to and from the backlight driver in the kernel.

Summary

The brightness C example project creates a GTK+ UI for controlling the backlight-brightness on a EMAC PPC-E7, SoM-9307 or just about any other board with an LCD.