Reverse engineering the ZMAi-90 DIN rail meter/switch and integrating with Hass.io using Tasmota - Part 2

I finished the first post with  a tone of optimism, in spite of not being quite there yet. But this time I'm bringing the complete story, with something which hopefully can be a useful takeaway for most users.

Initial analysis of the MCU communication

After figuring out what kind of communication was going on between the ESP8266 and the Vangotech V9821 chip (the specialized MCU which does all the metering functions - and a bit more which I will go in detail afterwards), I got a bit puzzled with the output and its consistency. I first connected a known AC current source through the shunt mounted in the relay's output rail, and in the middle of a stream of garbage, some values seemed consistent with the current I was putting and  being shown in the device's display.

I still cracked my mind at trying to figure out a pattern (I felt as if I was trying to incarnate John Nash while looking for patterns in seemingly chaotic data), and trying to prove assumptions such as the last byte being a checksum. But nothing fruitful came out of that first iteration.

Attempting to reverse engineer a home automation oriented smart-meter - Part 1

In my quest to make my house smarter, but still looking forward to keep having control over it, I have been doing some additions which I plan to further document here, in the short term.

In the meantime I thought it would be more relevant to share my findings in regard to a device a bit more "exhotic" than the Sonoff boxes we are all used to. This device is a sort of a miniature smartmeter that fits in a DIN rail next to the circuit breakers.

Just like the Sonoff modules, it also pairs with your WLAN, and connects to a cloud service. Instead of the eWeLink cloud to which Sonoff devices connect to, in this case it connects to another relatively popular cloud service called Tuya.

Waking up devices in Hass.io (Home Assistant)

This is a quick post on a challenge I had to overcome while integrating my SmartTV (an LG TV 55UJ620V) with Hass.io.

I wanted Hass.io to be able to turn on the TV (as such allowing automations to be built on top of it, or for example turning it on through a voice command via Google Assistant). As such I first resorted to using the Home Assistant Wake on LAN built in integration (https://www.home-assistant.io/integrations/wake_on_lan/). It kind of worked, but was not very reliable (perhaps 2 out of 5 times it would work).

I knew that by definition, the way that (Wake-up On LAN) WOL is implemented is inherently unreliable: essentially the target (dormant) device is expecting a frame with a specific pattern of bytes. If it receives that frame, it wakes up the host, otherwise nothing happens. The device will normally scan for that pattern of bytes in the frame regardless of the type of transport level protocol it may be on top of. In the case of WiFi in particular, there is the probability (high or low, depending on the network conditions) of that single frame not reaching the destination. This probability increases with the more hops we have in between.

With this Hass.io implementation I was requiring the magic packet to be sent from a host (the Raspberry Pi where I keep Hass.io running) that is in a separate router vlan, from where the TV is (these are connected via Ethernet and WiFi respectively):