Unexpected behavior of ws2801 when headless

Question

I am using a raspberry pi 3 with a fresh installation of raspbian-lite to control a strip of ws2801 RGB leds. I followed the tutorial found here: https://tutorials-raspberrypi.com/how-to-control-a-raspberry-pi-ws2801-rgb-led-strip/ and as long as I have an hdmi display connected the example code works fine. I can even ssh into the pi and run the example code and as long as there is an hdmi display connected to the pi it will work fine.

The trouble comes in when I unplug the hdmi display. If I run the example code without a display plugged in the strip will light up and sort-of do the animations it is supposed to do but it is very glitchy. It seems like something is interrupting the sending of data on the spi bus and only partial packets are being sent.

Has anyone experienced anything like this before?

Answer 1

I figured out what was wrong. The display and the power supply are plugged into the same strip and ultimately share a common ground which is what was making things work.

I was missing one thing from the wiring diagram in the tutorial...Connecting the ground of the led strip to the pi. When I tested this yesterday with my arduino I didn't have to do that. My laziness created my own problem.