Read out electricity meter Iskra MT681 (Stromzähler)

Motivation

After installing 2 photovoltaic modules on my balcony (check out the project documentation), my electricity provider unfortunately replaced my old electricity meter (that rotated backwards when PV production exceeded my consumption).

As the new meter has an optic interface, I decided to try to read it out to have at least some benefit of the replacement...

A great documentation (in German) on how to read out different electricity meters was my starting point.

Hardware

My electricity meter is an Iskra eHZ-MT681-D4A52-K0p

For the readout I bought an all-inclusive product for 40€ at eBay. It bundles

• Hichi IR sensor
• micro controller ESP01S (Wi-Fi and MicroUSB power connector)
• pre-installed software Tasmota V13.3

So no Arduino programming and no soldering ;-)

Setup

Following the manual of the sensor I performed these steps

• connect laptop to sensor's Wi-Fi
• enter my Wi-Fi credentials
• switch back to my Wi-Fi
• access sensor webinterface
• setup the electricity meter via console -> script (see below)
• activating the script
• -> data appears on the main page of the UI
• set Logging->TelePeriod to 15 for readout every 15s
• (optionally) configure access to my MQTT server

Tasmota script for Iskra MT681-D4A52-K0p

• copied from Tasmota documentation
• skipping/commenting out the last line of the static Meter_id

>D
>B
=>sensor53 r
>M 1
+1,3,s,0,9600,MT681
1,77070100010800ff@1000,Verbrauch,kWh,Total_in,4
1,77070100100700ff@1,Leistung,W,Power_cur,0
1,77070100020800ff@1000,Erzeugung,kWh,Total_out,4
; 1,77070100000009ff@#,Service ID,,Meter_id,0|

Set timezone

see doc in webinterface open console to read and change the timezone TimeZone show current timezone TimeZone 99 use timezone configured by TimeDst and TimeStd

tasmotatimezone.com provides more info, in my case it suggests this command Backlog Latitude 49.5928616; Longitude 11.0056; TimeDST 0,0,3,1,1,120; TimeSTD 0,0,10,1,1,60; TimeZone 99

Data visualization

In device webinterface

Here is described, how to upload a Tasmota firmware and script, that provides data visualization on the webinterface of the device. I did not try that.

In Grafana

Instead, I use some existing pieces of software on a Raspberry Pi 3b "server".

• activate MQTT protocol in the sensor webinterface to send the data
• Python script to receive the data via MQTT
• InfluxDB to store the data
• Grafana to visualize the data

See example_code for Python example and Grafana dashboard model.

In HomeAssistant

Alternative setup could be to use HomeAssistant to receive the data via MQTT, with is also described in the HowTo.

Tasmota commands via MQTT

see Tasmota documentation

Sending an empty message body, results in the device responding with its current value.

mosquitto_pub -u mqtt_user -P mqtt_passwd -t "cmnd/tasmota_MT681/webserver" -m ""

Power Saving

Disable webinterface

After setting up the device and connecting to MQTT broker, I decided to turn off the webinterface, to hopefully reduce the power consumption. (here tasmota_MT681 is the name of my device)

mosquitto_pub -u mqtt_user -P mqtt_passwd -t "cmnd/tasmota_MT681/webserver" -m "0"

Sending frequency

Reduce the devices sending frequency to every 300s

mosquitto_pub -u mqtt_user -P mqtt_passwd -t "cmnd/tasmota_MT681/TelePeriod" -m "300"

Since attaching the device to a power source, instead of a power bank (see below), I use 10s during the day and 30s in the night. Switching is triggered via crontab of my raspi.

Sleep and Dynamic Sleep

see Tasmota Energy-Saving docu on Sleep vs. Dynamic Sleep (currently I use default Dynamic Sleep and 50ms)

set longer sleep time of 200ms (default is 50)

mosquitto_pub -u mqtt_user -P mqtt_passwd -t "cmnd/tasmota_MT681/Sleep" -m "200"

Switch from Dynamic Sleep (0) to normal Sleep (1)

mosquitto_pub -u mqtt_user -P mqtt_passwd -t "cmnd/tasmota_MT681/SetOption60" -m "1"

Power Supply

Since I had no power plug in the meter cabinet available, I used an USB power bank. Unfortunately, that one only lasted for a couple of days, despite my power saving efforts. So I installed a 5V power source MEAN WELL HDR-15-5 behind a new fuse in the meter cabinet.