Zero Blinking Lights

In between tackling a work project that kind of spilled over into the weekend and watching TechReady¹ sessions, I decided to fix an annoyance I had with the Raspberry Pi Zero.

Like I wrote the other day, the Zero supports USB OTG, and you can get it to act as a virtual Ethernet port by simply appending dtoverlay=dwc2 at the end of config.txt to patch the device tree and add modules-load=dwc2,g_ether to cmdline.txt just after rootwait.

That’s the work of a few seconds, and when hooked up to another computer, the Zero will simply set itself up with an IPv4 local link address and announce itself over Bonjour – which works wonderfully with my Mac and most Linux boxes, including other Pis. All I need to do is ssh [email protected] and I’m set.

If I need to install or update something, it’s trivial to share my network connection to it – but that just doesn’t work under Windows for me. I already have enough trouble with Docker, the Hyper-V virtual switch and access to corporate Wi-Fi (right now, for whatever reason, they’re mutually exclusive), so I decided not to fiddle with my work laptop that deeply and figure out a way to know the Zero’s link-local address.

Fortunately, I had a Scroll pHAT lying around, so all I really needed to do was solder a set of headers onto the Zero…

…and tweak the network config (on post-up for usb0) to run a little script to display the IP address on it:

#!/usr/bin/env python

from scrollphat import write_string, scroll, clear, set_brightness
from socket import socket, AF_INET, SOCK_DGRAM
from time import sleep

def get_ip_address():
    """Fool the network stack into telling us what the outbound interface is without actually connecting anywhere"""
    s = socket(AF_INET, SOCK_DGRAM)
    s.connect(("8.8.8.8", 53))
    return s.getsockname()[0]

set_brightness(3)
write_string(" IP: %s " % get_ip_address())
for i in range(0,128):
    sleep(0.15)
    scroll()
clear()

It’s a bit clunky and marquees have always been a tad cheesy, but it works and I can now move on to prototyping a few things. Also, I had to dim down the brightness a tad because those LEDs pack a serious punch. So if everything else fails, I now have myself an Internet-enabled reading light…