Heat meter through digital seven segment LCD

If you have a (heat) meter with a seven segment display, this guide explains how to add this to domoticz.

Hardware

• Landis+Gyr Ultraheat
• Camera
• Optional: USB light (for )

Units

Meter units is in GJ, with 3 decimal digits (e.g. 271.199 GJ). Value we recognize is in MJ because we ignore the decimal point in OCR. Domoticz units are in m^3, with 2 decimal digits (e.g. 3581.92 m^3) -- internally might be stored with higher precision, again not visible through JSON api because of poor interface.

Conversion unit is 13.20772 m^3 gas/GJ, resolution is 0.01 m^3 for total count or 0.001 m^3 for daily count. For electric energy, conversion would be 277.7777 kWh/GJ.

Software

Pre-requisities

py27-requests, opencv-python

On Mac (with MacPorts):

port install py27-pip py27-requests
sudo pip-2.7 install opencv-python

On Debian/Ubuntu:

sudo apt install python-opencv

Test images / point camera

raspistill --datetime -v -o cam_%d.jpg -t 0

Calibrate software

use get_digits.py script:

./get_digits.py --calibrate

or if you want to calibrate on an image taken previously

raspistill --datetime -v -o cam_%d.jpg -t 0
./get_digits.py --rotate 180 --ndigit 7 --calibrate cam_*.jpg

or using esp32/home-assistant integration, see heatmeter.sh

Get paramters: --roi 761 907 1494 901 1502 748 784 744 --digwidth 80 --segwidth 25 --segthresh 0.25

Set up domoticz

0. Set gas meter divisor to 1000 (not 100 as is standard)
1. Create dummy hardware
2. On this dummy hardware, create gas meter (Counter Incremental)
   1. Set meter to gas type: utility -> edit -> Type: Gas
   2. Set meter offset: utility -> edit -> Meter offset:
3. On this dummy hardware, create power meter (Electric (Instant+Counter)) -- N.B. Currently not supported because of JSON limitations
   1. Set power meter to 'from device': utility -> edit -> "From device", otherwise the consumption is computed from the power
4. Note down idx of two meters created
5. Test updating meters manually using e.g. curl:
   1. get data: curl -k "https://127.0.0.1:10443/json.htm?type=devices&rid=<idx>"
   2. update power meter: curl -k "https://127.0.0.1:10443/json.htm?type=command&param=udevice&idx=<idx>&svalue=<power in Watt>;<usage in Wh>"
   3. update power meter: curl -k "https://127.0.0.1:10443/json.htm?type=command&param=udevice&idx=<idx>&svalue=<power in Watt>;<usage in Wh>"
   4. Once done with testing and you understand how domoticz meters work, delete and recreate meters to start off fresh
6. Update get_digits script
   1. Update meter idx
   2. Update meter unit / type (e.g. gas / power), update conversion factors where necessary

Set up influxdb

Not covered here

Delete data points

To delete erroneous data from influxdb, use the timestamp as semi-unique identifier. Note that this will also delete other measurements taken at the identical time! Alternatively, overwrite the value with something more sensical if this is a problem.

SELECT * FROM energyv3 WHERE time=\'$i\'
curl -G 'http://localhost:8086/query?db=smarthome' --data-urlencode 'q=DELETE FROM energyv3 WHERE time=\'$i\''

Run script

Add script to crontab -e, run e.g. every minute:

*/2 * * * * ./get_digits.py  --rotate 180 --ndigit 7 --roi 739 703 1487 699 1497 537 757 544 --digwidth 90 --segwidth 30 --segthresh 0.3 --domoticz https 127.0.0.1 10443 28 --influxdb http 127.0.0.1 8086 database "measurement value="

Alternatives

• https://github.com/jiweibo/SSOCR looks promising
• https://www.unix-ag.uni-kl.de/~auerswal/ssocr/ is very sensitive to noise, didn't work for me
• tesseract / character recognition is overkill given the simplicity of seven segment LCD
• openCV's adaptive thresholding didn't work for me

References

• https://www.pyimagesearch.com/2017/02/13/recognizing-digits-with-opencv-and-python
• https://www.unix-ag.uni-kl.de/~auerswal/ssocr/
• https://github.com/jiweibo/SSOCR
• https://www.swarthmore.edu/NatSci/mzucker1/e27_s2016/install_opencv.html
• https://github.com/arturaugusto/display_ocr
• https://hackaday.com/2013/01/03/ocr-automatically-reads-a-power-meter/