Monitoring your appliances’ power

I recently posted about real-time data from your smart meter and all was good, but then thread by Robin Hawkes on Twitter caught my eye:

These devices connect to your WiFi network and allow you to switch a connected device on or off, on a schedule if you require, and also monitor power consumption. That last bit is the most important for me – knowing how much energy I’m consuming.

After researching Tasmota, an open firmware for simple home automation devices, and checking a bunch of reviews on the TP-Link Tapo P110‘s firmware, it looked like these P110s would do just what I needed – simple power monitoring for not much of an initial outlay.

LocalBytes were out of stock of both of these items when I looked, so I took the plunge and ordered one from elsewhere. Well, I ordered eight because I was feeling quite bold.

Initial setup

Trivial. Download the Android (or iOS presumably) app, plug in a device, find its wireless network and configure it to connect to your wireless network. It reboots and that’s about it.

Firmware updates can be scheduled automatically, but I don’t know whether this will switch the power off to any connected device or not. Something to check later.

Control and monitoring

The mobile app makes it quite easy to switch a device on and off, to set a schedule, and to see power consumption. But it’s a mobile app, and I want the data somewhere I can analyse it easily.

Home Assistant to the rescue! Running HA under Docker is really easy if you know Docker. I could have re-purposed one of my Raspberry Pi as I can’t get a new OpenVMS Community licence for VAX any more, but I wanted to try HA quickly to see if it fitted my needs.

Support for the P110 devices doesn’t come as standard, but there’s a community-written workaround for that. A little fiddly and not really what I’d expect, but it works.

Next steps

Oh boy, there’s a lot I want to do.

First off, I want to push the sensor data out from these devices in to an MQTT server such as Mosquitto and have Telegraf pull this data in to a time-series database so I can visualise it with Grafana.

Other things I want to do include automatically checking my Google Calendar and setting the heating to come up early when I’m doing a morning clinic, or having it come on a bit later when I’m at home that day. I want to get an inline power switch for my porch light and turn that on between dusk and sometime around midnight.

Slack’s verbose logging on Linux

I’m a long-time user of Slack. Many of my customers use it, and we share channels to exchange information and work better together. I’m also a member of a number of other Slack workspaces for various projects.

The Linux app is great, with one exception – it’s very heavy on logging:

slack.desktop[27635]: [09/12/22, 13:58:26:475] info: API-Q cb429c3b-1662987506.474 client.shouldReload called with reason: polling
slack.desktop[27635]: [09/12/22, 13:58:26:475] info: API-Q cb429c3b-1662987506.474 client.shouldReload is ENQUEUED
slack.desktop[27635]: [09/12/22, 13:58:26:487] info: API-Q cb429c3b-1662987506.474 client.shouldReload is ACTIVE
slack.desktop[27635]: [09/12/22, 13:58:26:631] info: API-Q cb429c3b-1662987506.474 client.shouldReload is RESOLVED
slack.desktop[27635]: [09/12/22, 13:58:26:632] info: [MIN-VERSION] No need to reload
slack.desktop[27635]: [09/12/22, 13:58:34:433] info: DND_V2 Checking for changes in DND status for the following members: XXXXXXXXX,XXXXXXXXX,XXXXXXXXX
slack.desktop[27635]: [09/12/22, 13:58:34:435] info: DND_V2 Will check for changes in DND status again in 1.43 minutes

I don’t want my syslog littered with information that’s not useful! Other applications such as gnome-shell are pretty good at being verbose, but not to Slack’s extent.

The fix, thankfully, is super easy. Create a file named /etc/rsyslog.d/20-slack.conf with the following:

Drop info log messages from Slack
:rawmsg,contains,"slack.desktop" /dev/null
& stop

Run sudo systemctl reload rsyslogd and ta-da, no more Slack logging in your syslog.

Real-time Smart Meter data

A year or two ago, I took the plunge and had a smart meter installed. I naively thought that being able to read energy usage was a simple case of connecting a ConBee-II or similar to the ZigBee HAN.

To save anyone else from going through the same range of emotions as I did, here’s how you can read your own smart meter data.

Technology primer

Your electricity meter has two parts – a metering device, and a communications device located at the top. The electricity meter periodically sends energy usage information over a communications network to your supplier. It’s easy when you have a continual supply of electricity.

If you have a gas meter, it doesn’t have its own communications device. To do so would require a power supply to the gas meter – readily available on an electricity meter. Instead, the gas meter sends energy usage to the electricity meter every 30 minutes and therefore only has a long-life battery installed.

Getting access to the data

There are two ways to get access to real-time electricity and real-ish time gas usage data. Neither of them involve pairing your own device.

The best option is to buy a combined In-Home Display (IHD) and Customer Access Device (CAD) from Glow (Hildebrand Technology) sell a combined in-home display (IHD) and Customer Access Device (CAD) for around £65. This arrives already paired with your smart meter, and you connect it to your home wireless network, and it sends out data from your smart meter to an MQTT server (which can be on your local network too), ready for you to consume yourself. The device needs Internet access for firmware updates, but your data is kept locally.

The other option is to use intermediary such as Glowmarkt, who are a DCC Other User and can request your metering data from the Data Communications Company, then make it available to you. This is a straightforward process, although you need to go through an industry-mandated security process to prove you are requesting access to your data and not somebody else’s. They make your data available via their MQTT server, although it’s not at the same level of granularity as having your own IHD/CAD.

The data

You can use the CAD as a simple IHD – it’s a lot prettier than the one supplied by my energy supplier (which I can still use). Electricity usage arrives every few seconds, with gas usage as and when the metering equipment makes it available.

The real power comes when you work with data in real-time, or at least as close to real-time as it’ll give you. Want to work out how much the tumble dryer cost to run? Or find out whether you’re OK with having your home a little cooler to save a bunch of energy?

Data format

The MQTT messages you receive are in JSON format, and contain data for three ‘clusters’ – Metering (0x0702), Prepayment (0x0705) and Device Management (0x0708). Each of these clusters has an attribute set – the Metering cluster presents the Reading Information Set (0x00), Formatting (0x03) and Historical Consumption (0x04). Finally, each attribute set has a set of key/value pairs. From this, you can decode that cluster 0x0708 (Device Management), attribute set 0x01 (Supplier Control Attribute Set) value 0x01 is the provider name.

Since the data is sent in JSON format, it’s quite easy to parse. If you want to dive straight in to the detail about what clusters and attribute sets are, the ZigBee Smart Energy Standard is available, although at 628 pages, it’s a heavy read.


The entire process was quick – the CAD arrived within a day or two of placing my order and was ready to use the moment I plugged it in. Getting my data in real-time took a little longer – it’s a manual process for the staff at Glow, but once it’s set up, that’s it.

The only problem is that there’s no formal support. For the first six months, the CAD disconnected itself from my WiFi network for no reason. Despite posting about my issue, there’s was no progress on it – but out of the blue, a firmware update arrived which fixed the issue.

Is the lack of formal support a problem? Likely not – unless you’re having an issue. Since the firmware update, I’ve had no problems with the IHD, other than a lack of time to play with and analyse the data.

Recommendation: go buy one!

Working around ‘Key is stored in legacy trusted.gpg keyring (/etc/apt/trusted.gpg)’

If a webpage tells you to run a command to import a GPG key when setting up an APT repository, it isn’t necessarily correct! Newer versions of Ubuntu no longer use apt-key and /etc/apt/trusted.gpg, preferring you put repository GPG keys in a file under /etc/apt/trusted.gpg.d.

Having recently reinstalled my desktop and not realising this, I had this exceedingly annoying error:

W: Key is stored in legacy trusted.gpg keyring (/etc/apt/trusted.gpg), see the DEPRECATION section in apt-key(8) for details.

This is one of the kinds of errors that tells you what you shouldn’t do, and isn’t too helpful about guiding you to what you should do.

As this is an easily forgettable problem, here’s how to fix it.

First, list the keys in /etc/apt/trusted.gpg:

gpg --keyring /etc/apt/trusted.gpg --list-keys

You will see a list of keys similar to the following:

pub rsa4096 2021-10-27 [SC] [expires: 2023-01-20]
uid [ unknown] Spotify Public Repository Signing Key

pub rsa4096 2013-11-19 [SC] [expires: 2027-11-11]
uid [ unknown] Code Signing (v1)
sub rsa4096 2013-11-19 [E] [expires: 2027-11-11]

pub rsa4096 2014-01-13 [SCEA] [expired: 2019-01-12]
uid [ expired] packagecloud ops (production key)

pub rsa4096 2016-02-18 [SCEA]
uid [ unknown] (
sub rsa4096 2016-02-18 [SEA]

For each of the keys, find the key ID – the long hexadecimal string on the second line, and run the following command:

gpg --keyring /etc/apt/trusted.gpg --export <key-id> | sudo tee /etc/apt/trusted.gpg/<repository>.gpg

Finally, tidy up after yourself by deleting the key from trusted.gpg:

sudo gpg --keyring /etc/apt/trusted.gpg --delete-key <key-id>

You can even specify multiple keys on the command line.

And that’s it.