Airport Express/Extreme and IoT Devices

At some point (I think it was when I needed to track down what device on my network was consuming multi-gigabytes of data daily), I moved to OpenWRT on my gateway router. Prior to that, I’d just used an Airport Express, and several other Extreme and Express units around my house.

I still use the Express (and Extreme) units for WiFi. Until yesterday, I’d repurposed a couple of older Airport Express units that were running the IoT network themselves. I could have had those as an isolated network, but it’s convenient to be able to have some connection between the two. I do use a set of firewall rules to allow devices on LAN to access IOT, but not vice-versa. This allows me to update the firmware on my esphome devices without having to switch WiFi networks.

So, I had used a VLAN (and made it untagged on one port of the switch in the gateway router) for IOT. Then I had this connected to an older AirPort Express, which created the network. Then, and additional (only linked wirelessly) Airport Express extended this network.

I had thought that it would be neat to have the regular WiFi access points also creating the IOT WiFi network: indeed I nearly bought more Ubiquiti APs to install here just to do that (I put them in the beach houses).

I’m glad I didn’t: it turns out the the Guest Network functionality on the Airport devices can be repurposed for what I needed.

The magic bit of information is that the Airport base stations uses VLAN untagged ethernet frames for the main WiFi network, and VLAN 1003 tagged ethernet frames for the “Guest” network.

So all I needed to do was change the VLAN id I was using for IOT, and ensure that my router (and managed switch(es)) were passing through tagged frames for VLAN 1003 to all relevant devices. And then configure the IOT network on the existing Airport base stations. Oh, and unplug the two standalone Airport Express units.


The other thing I was able to do is add virtual Ethernet Adapters on some devices so they also exist on the IOT VLAN. This turned out to be much easier on a Mac than I thought it would be thanks to Apple Support than it was on Raspberry Pi, although not by much.

Sonoff Basic unable to connect to Wifi on AC power

I have a few of the Sonoff Basic devices. I’d flashed one of them with a custom firmware before, but then was using the stock firmware, and having them operate in LAN mode.

However, that’s less than awesome: for one, it means I need to have (and maintain) a custom service running somewhere on my network, and because of the way you need to provision them, it’s hard to move this to a different machine.

With ESPhome, I’ve started re-flashing my old ESP8266 devices, so I had a go at some of the Sonoff. Neither of the ones I had installed (with the stock firwmare) had headers soldered onto the UART pins, but it turned out that one of my USB-UART devices had the pins in the correct order that I was able to (after disconnecting it from the mains, of course), hold the button down, press the USB-UART device into position, and then connect the USB port. After a couple of seconds, I released the button, and, eventually (after a couple of tries), have the device in “flash” mode.

Of course, I only discovered this after totally disconnecting one, soldering on some header pins and then connecting the device using hookup wires.

Then I uploaded the custom firmware. At which point I was able to re-upload firmware using the OTA mode, which means I no longer had to juggle the serial connector, USB and GPIO0 button.

So, I then flashed another one, this time without having to solder, and had both of them configured as devices on my IoT network.

But, there was a problem. They would only connect to the Wifi when they were connected to the serial connector. When I disconnected the serial port, and reconnected them to the mains supply, they would operate correctly, but would not connect to Wifi. Even though one of them was literally less than a metre from the router.

I did a bit of research, and there apparently are a batch that are like this. Tasmota firmware has issues that mention this on GitHub, but then in those issues they are marked as “resolved”. Unfortunately there was not really a good resolution - more than likely it was just some type of stale-bot just closing issues that had not been updated in a certain time frame. At least one of these suggested that a newer firmware worked, but that was no good for me.

A couple of these issues identified that there was a missing capacitor, but one of them mentioned that they had soldered together the 3v3 supply, and the RX and TX pins.

So, I ran some experiments. Connecting the 3v3 pin to either of those other pins had no effect, but connecting the RX and TX together suddenly allowed my device with the header pins to connect!

Luckily, these pins are adjacent, so I found a jumper (I remember when these were on just about every hard drive, but I couldn’t find one today with a single pin), and hooked it up.

All good!

Unfortunately, when putting it back together I didn’t align the top cover with the button correctly, so I managed to break that. Which just means I can’t control the switch directly, only remotely. That’s pretty annoying (it’s one of the reasons I went with Sonoff over some other solutions), but at least it works on HomeKit now.