• Gas counter via KY-021 Mini reed magnet
• KY-021 circuit
  • Measuring pulse with PullUp
  • Measuring pulse with PullDown
• Test send and receive data via MQTT message service
  • Install mosquitto broker on OpenWrt router
  • Test mosquitto message exchange on OpenWrt router
  • Test mosquitto message exchange on Raspberry
• Collecting data via mosquitto
  • Create another client user for listening
  • Test mosquitto message exchange from Raspberry with QoS 1 to
  • init script for OpenWrt
  • Verify init script for OpenWrt is working
• Collect initial data
  • Analyse data

Gas counter via KY-021 Mini reed magnet

Near Stuttgart, Germany, the gas box from the supplier is a GT4 G4 from 2005. It says that one magnetic pulse equals: 1 imp=0,01 m3. The red box is marking a place for putting a magnet for reading the pulses.

I thought it could be a funny project to count the gas, and see gas consumption:

• if usage happens during showering in the morning
• or usage happens during heating in the night / evening

Plan:

• Find a magnetic sensor that picks up the magnetic pulse
• Collect the pulse and send data somewhere for calculation or viewing

The example witill be an Raspberry Pi 4B, with the Explorer Hat Pro from Pimoroni, which will be used for initial circuit exploration on the mini breadboard.

The Explorer Hat Pro is an older, now discontinued, product. I initially tried Raspberry Pi OS 64-bit Bookworm, but I got problems with python installation and sound card for the examples/drums.py. After I downgraded to Legacy Bullseye, 64-bit, Lite, then installation and examples worked as intended.

After verification, the story is continued with a battery powered NodeMCU.

KY-021 circuit

I conveniently found someone selling 3d-printed plastic holder with KY-021 Mini reed magnet for 16 euro on ebay.de. The internal circuit is depicted here

In the default configuration with sensor on the left pin, 5V on the middle pin and ground on the right pin, with internal 10k R1 resistor to lower current. With no magnet, the reed contact is open, we should measure a HIGH/1 voltage signal. With a magnet pulse, the contact closes, voltage is grounded and a LOW/0 voltage is measured.

Measuring pulse with PullUp

If we use a Rasperry with a PullUp/PullDown resistor, we would normally initialize the GPIO input pin with something like GPIO.setup(23, GPIO.IN, pull_up_down=GPIO.PUD_UP), to make sure it's initially HIGH and not in a floating state. If the Pin is in a floating stage, it is susceptible to random electromagnetic radiation or static from you, from any devices near or far and from the environment. Using this command, we use built-in pull-up resistors which can be enabled in software.

BUT, when we use the Explorer Hat Pro, Pi's GPIO pin is after the buffer, input signals will not be pulled up or down by enabling the Pi's onboard pull resistors. So, we need to build a PullUp resistor ourselves.

And we test the circuit with the code up-input-event.py

Measuring pulse with PullDown

With a PullDown transistor, we should initially measure a LOW/0. With a magnet pulse, the contact closes and a HIGHT/1 is measured.

To achieve this, switch 5V/GND on the KY-021 pins, make a 10k R between Input 1 and GND (instead of 5V) and switch the on/off of led diode in code.

And we test the circuit with the code down-input-event.py

Test send and receive data via MQTT message service

We will install mosquitto as a broker on a device/computer that is always on. In this example, a GL.iNet GL-A1300 (Slate Plus) with OpenWrt 23.05.

Install mosquitto broker on OpenWrt router

# Install
opkg update
opkg install mosquitto-ssl
opkg install mosquitto-client-ssl libmosquitto-ssl
# Optional, if configuration via click in Luci is preferred.
# opkg install luci-app-mosquitto

# Make sure mosquitto service can read/write 
chown root:mosquitto /etc/mosquitto
chmod g+w /etc/mosquitto/
# Create mosquitto user: gasuser
mosquitto_passwd -c /etc/mosquitto/passwd gasuser
# Give passwword: helloworld
# Change owner
chown mosquitto:mosquitto /etc/mosquitto/passwd


# Edit configuration file
nano /etc/mosquitto/mosquitto.conf
# Set values
allow_anonymous false
password_file /etc/mosquitto/passwd
listener 1883 0.0.0.0
persistence true
persistence_file mosquitto.db
persistence_location /etc/mosquitto

# Check
ls -la /etc/mosquitto/
grep -v '^#' /etc/mosquitto/mosquitto.conf | grep -v -e '^$'
mosquitto --verbose --config-file /etc/mosquitto/mosquitto.conf 
# If no errors then break.

# Enable, Restart
/etc/init.d/mosquitto enable
/etc/init.d/mosquitto restart

Test mosquitto message exchange on OpenWrt router

Since, the Access Point is named slateplus in luci system->system->hostname we can use slateplus.lan as hostname.

Login 2x with ssh to the OpenWrt router.

# Try from 1 terminal and listen
mosquitto_sub -h slateplus.lan  -u "gasuser" -P "helloworld" -t test
# Publish from other terminal
mosquitto_pub -h slateplus.lan  -u "gasuser" -P "helloworld" -t test -m "Testing"

Test mosquitto message exchange on Raspberry

Install mosquitto client on Raspberry

# Bash client
sudo apt-get update
sudo apt-get install mosquitto-clients
# Python module
sudo pip install paho-mqtt

Test publish with --retain. When a client is subscribing, it always get retained messages-

# First Publish from other terminal
mosquitto_pub -h slateplus.lan  -u "gasuser" -P "helloworld" -r -t test -m "Testing Retain"

# Try from 1 terminal and see if retained message is there
mosquitto_sub -h slateplus.lan  -u "gasuser" -P "helloworld" -t test

With python code paho-mqtt.py, try to publish and watch subscription terminal.

Collecting data via mosquitto

Create another client user for listening

On OpenWrt router, create user and restart server

# Create user for reading
mosquitto_passwd -b /etc/mosquitto/passwd gasread Hello
# Pickup new password
/etc/init.d/mosquitto restart

Test mosquitto message exchange from Raspberry with QoS 1 to

Manuel for mosquitto_sub and mqtt. Listen with QoS and enable enable persistent client mode. With -v, topic is added prepended to message lines.

On OpenWrt router, listen

mosquitto_sub -h slateplus.lan  -u "gasread" -P "Hello" -v -t "sensors/gas/#" --qos 1 --id "gasread" --disable-clean-session 

On raspberry, run script gas-sensor.py.

Try to keep making magnetic pulses, while breaking and connecting again mosquitto_sub and see all messages is received.

init script for OpenWrt

We will make a script that starts on boot and save to file. The boot script gas_counter which is send to background with &.

# Make executable
chmod +x /etc/init.d/gas_counter

# Enable and start
/etc/init.d/gas_counter enable
# Check symlink creation 
ls -la /etc/rc.d/*gas_counter
# Check it's enabled.
/etc/init.d/gas_counter enabled && echo on
# Please note, that a "restart" only will do a stop() and not a start() again. The script itself is also killed.
/etc/init.d/gas_counter start

# See log
cat /root/gas_data.log

Verify init script for OpenWrt is working

On raspberry, run script gas-sensor.py.

Make some data with a small magnet.

On OpenWrt, follow data with

tail -f /root/gas_data.csv

Collect initial data

On OpenWrt:

/etc/init.d/gas_counter stop
rm /root/gas_data.*
/etc/init.d/gas_counter start

On raspberry:

sudo apt-get update
sudo apt-get install screen
screen 
# To detach this terminal session, press "CTRL + A", release, and then press "D"
# Attach
screen -list
screen -r 1950.pts-1.raspberrypi
# Start python
python gas-counter-magnetic/raspberry/gas-sensor.py

I needed to re-adjust the KY-021 board a few millimetersv up, so the reed contact was at the very top line of the blue plastic. When this was working, the initial current consumption was: 3345.71

Analyse data

Get and install miniforge. Install Visual Studio Code and install extensions python, Jupyter.

Create environment with miniconda and use analyse.ipynb

conda env create --file=environment.yml
# To update from file
conda activate gascounter
conda env update --name gascounter --file environment.yml --prune
conda activate gascounter

There is many pulses recorded at 6 and 7 in the morning. This makes sense, as the Gasherd is programmed to a "morning" program with warm water, starting at 6. And any showers around 8.30 after the morning run is keeping the gasherd busy the following hour.

Making a linear regression between observed consumption versus recorded number of pulses give a perfect regression, with fitted parameters:

• Slope consumption per pulse is: 0.010
• Initial consumption is: 3345.706