Hello world! Launch the Processing (2.2.1) IDE and load the first of our example programs: OPCstrandtest.

At the top of the code are these two lines:

OPC opc       = new OPC(this, "", 7890);
int numPixels = 256; // Set this to actual strand length

The first line holds the address of your OPC server device. We previously configured that in the Arduino code. The format here is just a little different though…instead of four comma-delimited values (192, 168, 0, 60), here it’s a string with period separators "". Edit the numbers to match the Arduino sketch.

Next line is the number of LEDs in your DotStar chain. This might be 64 for an 8x8 matrix, or 60 (or 144, etc.) for one meter of DotStar strip.

When you run this code (the top-left icon in the Processing window), after just a moment’s delay you should see the message “Connected to OPC server” and get a “chaser” down the DotStar chain that cycles between red, green and blue for each pass. Press the ESC key to stop the program.

If the colors appear in the wrong order (not red, green, blue), you’ll need to edit the Arduino sketch to match your particular DotStar hardware. This is explained near the bottom of the “Software” page.

If it runs slowly or stutters, especially with long LED runs, you may need to reduce the frame rate. Inside the setup() function you’ll see a call to frameRate(). It takes a single argument, the number of frames per second. The default (if not specified) is 60 frames per second…that’s usually fine with small projects, but with lots of LEDs you may need to dial it back, to perhaps 30 frames per second.

If you don’t see the “Connected” message and don’t get any LEDs: either the Server sketch on the Arduino can’t connect to the wireless network, or the address at the top of the Processing sketch is incorrect.

Do not continue until you have the led “chaser” working, and it’s cycling from red to green to blue.

This guide was first published on Apr 07, 2016. It was last updated on Mar 08, 2024.

This page (OPC Strandtest) was last updated on Mar 20, 2016.

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