Laptop Bridge¶

Python scripts for reading USB-connected gas analysers on a Windows or Linux laptop and pushing their data to the Raspberry Pi hub. This is an optional component — only needed if you have analysers connected via USB rather than the ESP32-based sensor units.

In our lab the laptop monitors two mixing bottle supplies:

Minir-5 (orange bottle) — 1–5% CO₂ mix, COM3 / /dev/ttyMINIR
K30 1% (clear bottle) — ambient/low CO₂ supply, COM4 / /dev/ttyK30

Files¶

File	Purpose
`minir_pusher.py`	Reads Minir-5 via ASCII protocol and pushes to Pi
`k30_pusher.py`	Reads K30 via Modbus binary protocol and pushes to Pi
`minir_calibration.py`	GUI calibration tool for the Minir-5
`k30_calibration.py`	GUI calibration tool for the K30

Requirements¶

pip install pyserial requests

On Linux, also add your user to the dialout group and log out/in:

sudo usermod -a -G dialout $USER

Configuration¶

Edit the top of each pusher script to match your setup:

# minir_pusher.py
SERIAL_PORT   = "COM3"          # Windows
# SERIAL_PORT = "/dev/ttyMINIR" # Linux (with udev rule)
PI_HOST       = "192.168.50.1"
PI_PORT       = 5000
SENSOR_ID     = "1-5% Mix"
LOCATION      = "Orange mixing bottle"

# k30_pusher.py
SERIAL_PORT   = "COM4"          # Windows
# SERIAL_PORT = "/dev/ttyK30"   # Linux (with udev rule)
PI_HOST       = "192.168.50.1"
PI_PORT       = 5000
SENSOR_ID     = "<400 ppm Mix"
LOCATION      = "Clear mixing bottle"

Running¶

Windows — run both scripts together¶

Create start_sensors.bat:

@echo off
cd /d C:\path\to\laptop-bridge
start "Minir5" python minir_pusher.py
start "K30"   python k30_pusher.py

Drop a shortcut to this file in shell:startup to run on login.

Linux — run as systemd services¶

Create /etc/systemd/system/minir-pusher.service:

[Unit]
Description=Minir-5 Gas Sensor Pusher
After=network.target

[Service]
ExecStart=/usr/bin/python3 /home/user/laptop-bridge/minir_pusher.py
Restart=always
RestartSec=10
User=user

[Install]
WantedBy=multi-user.target

Repeat for k30-pusher.service. Then:

sudo systemctl enable --now minir-pusher k30-pusher

Linux: Persistent Serial Port Names (recommended)¶

On Linux the USB serial ports can be assigned different device names (/dev/ttyUSB0, /dev/ttyUSB1) depending on plug order. Use udev rules to assign stable names.

Find the USB serial numbers:

udevadm info -a -n /dev/ttyUSB0 | grep -E "serial|idVendor|idProduct"
udevadm info -a -n /dev/ttyUSB1 | grep -E "serial|idVendor|idProduct"

Create /etc/udev/rules.d/99-gas-sensors.rules:

SUBSYSTEM=="tty", ATTRS{idVendor}=="XXXX", ATTRS{serial}=="MINIR_SERIAL_HERE", SYMLINK+="ttyMINIR"
SUBSYSTEM=="tty", ATTRS{idVendor}=="XXXX", ATTRS{serial}=="K30_SERIAL_HERE",   SYMLINK+="ttyK30"

Reload:

sudo udevadm control --reload-rules && sudo udevadm trigger

The devices will now always appear as /dev/ttyMINIR and /dev/ttyK30.

Protocols¶

Minir-5 (ASCII)¶

Command	Sends	Response	Description
`Z\r\n`	—	`Z XXXXX`	Read CO₂ — value × 10 = ppm
`U\r\n`	—	`U XXXXX`	Unlock for calibration
`X NNNN\r\n`	—	`X XXXXX`	Calibrate — NNNN = target_ppm / 10

Example: Z 03050 → 30,500 ppm

K30 (Modbus binary)¶

Bytes	Description
`FE 44 00 08 02 9F 25`	Read CO₂ command (7 bytes)
`FE 44 02 HH LL XX XX`	Response — CO₂ = (HH × 256 + LL) ppm

Example response FE 44 02 00 61 79 0C → bytes[3:5] = 0x00 0x61 = 97 ppm

Calibration Tools¶

The calibration tools (minir_calibration.py and k30_calibration.py) are standalone GUI applications built with Python's tkinter — no additional packages required beyond pyserial.

Important: The pusher script and calibration tool cannot both have the serial port open simultaneously. Stop the relevant pusher before running the calibration tool, then restart it afterwards.

K30 calibration tool¶

Connects to K30 on the selected COM port
Shows live CO₂ reading (updates every 5 seconds)
Provides 0 ppm and 400 ppm calibration buttons with confirmation dialogs
Calibration sequence: sends unlock command → calibration command → 8-second settle → reads back result
Includes on-screen reminders about the departmental compressed air line limitation

Minir-5 calibration tool¶

Connects to Minir-5 on the selected COM port
Shows live CO₂ reading (updates every 5 seconds)
Accepts any target concentration (free entry + presets at 1k, 5k, 10k, 20k, 30k, 50k ppm)
Calibration sequence: U unlock → X NNNN calibration command → settle → verify confirmed value
Warns if the sensor's confirmed calibration point differs from the target by more than 100 ppm

Troubleshooting¶

Problem	Action
`Cannot open COM3/COM4`	Check Device Manager — port may have changed number. Update `SERIAL_PORT` in script.
No data in Grafana	Confirm laptop is connected to `GasMonitor` WiFi. Check script log output for POST errors.
Readings are ×10 wrong	Verify Minir-5 multiplier — raw value × 10 = ppm for the Minir protocol.
K30 returns -1 or no response	Check USB cable and level shifter wiring. Try power-cycling the K30.
Calibration tool won't connect	Stop the pusher script first — both tools cannot share the serial port.