EDIT: (2021-09-19): After some back and forth with /u/Laxarus, there is now a simpler method! The snmp platform still does not support setting device_class, but wrapping the sensor in another template sensor is not required; just do so in your customize.yaml. I have called this out below.

This is another quick “here’s how I did it, hope this help” post.

In preparation for the inevitable grid brownouts that summer 2021 would bring, I installed a rather beefy UPS for my home network / lab. After some browsing, I discovered a local eWaste liquidator with a really good deal on some second-hand APC UPSs.

UPDATE: (2021-10-22): Tasmota 9.5.0 has been superseded by the new Tasmota 10.0.0 release. This release works perfectly with the rules/automation outlined below; you no longer need to avoid the problematic 9.5 release with the DS03. I am extremely grateful to every one of the people that contributes to the Tasmota project to keep it improving!

Stack/signal lights are everywhere in industrial applications for good reason: they’re a compact and relatively information-dense indicator system. They always seemed like the kind of indicator that only people with expensive machines needed. Until I found that they can be had for just under $6/light from Ali Express, that is.

This is “reference” post for anybody else that happens to have this same very specific problem.

I was looking for a way to incorporate some of the many cheap / industrial grade sensors from AliExpress with Home Assistant. Long story short: almost everything electronic in the industrial space uses Modbus to communicate, typically with a PLC. While Home Assistant does have support for the Modbus protocol, but wanted to use a PLC that could manage the sensors directly and expose the values over the network in a more standard format; MQTT.

The APC AP7900 is a 1U single phase PDU with 8 switchable outlets and a network interface. It’s been EoL’d and can be had for less than 20% of it’s original price on eBay. The network interface is so underpowered tha it can’t support any modern cryptographic ciphers.

So with that, here’s a revised copy of my notes from the process of getting the device reset, updated and monitored.