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Connecting DS18B20 Temperature Sensors to RS485 Bus and Raspberry Pi

Table of Contents

  1. Project Overview
  2. Hardware Setup
  3. Connecting the Hardware
  4. Software Setup - The Fun Begins
  5. Installing My Python Script
  6. Testing the Connection
  7. Reading Temperatures Like a Boss
  8. Calibrating Your Sensors
  9. Automation and Monitoring
  10. Troubleshooting (When Shit Hits the Fan)
  11. Conclusion
  12. Additional Resources

Project Overview

I’m in the middle of migrating from my old home automation setup based on Raspberry Pi Automation HAT connected to temperature sensors via 1-wire bus to a more robust RS485 bus architecture. Why? Because I want to move my Raspberry Pi out of my electrical box to a rackmount server and maybe in the future move all computing to the cloud or at least a Kubernetes/K3s cluster.

Basically, 1-wire sucks for long distances and RS485 is way cooler.

So I bought some new DS18B20 sensors with RS485 interface (R4DCB08 module) from AliExpress and decided to document my journey with them.

Also, I created a Python script to make reading data from multiple DS18B20 sensors way easier than it should be: https://github.com/CalmWookie/R4DCB08-Python

Hardware Setup

Here’s what you need to get this party started:

  1. Raspberry Pi: Any model with USB ports. I actually used my Mac for most of the development because why not.
  2. RS485 to USB Converter: This magical device lets you connect RS485 to USB. Get a decent one, the cheap ones are… cheap.
  3. DS18B20 Sensors: I used waterproof ones because water and electronics don’t mix well (shocking, I know).
  4. Wiring: Twisted pair cables work great. Cat5 cable is perfect and you probably have some lying around.
  5. 120Ohm Resistor: For terminating the RS485 bus. This is your first troubleshooting step when things don’t work.
  6. R4DCB08 Module: The star of the show - RS485 to 1-wire adapter supporting up to 8 DS18B20 sensors.

Connecting the Hardware

This part is pretty straightforward, but let me break it down for you:

  1. USB Connection: Plug your RS485 to USB converter into your Raspberry Pi (or whatever computer you’re using).
  2. RS485 Wiring: Connect the A and B lines from your converter to the corresponding A and B terminals on the R4DCB08. Don’t mix these up unless you enjoy debugging.
  3. DS18B20 Sensors: Connect your sensors to the R4DCB08:
    • VCC (RED wire) goes to VCC terminal
    • GND (BLACK wire) goes to GND terminal
    • DQ (YELLOW wire) goes to one of channels 1-8
  4. Termination: If your cable run is longer than a few meters, slap a 120Ohm resistor between A and B lines at both ends. Your future self will thank you.

R4DCB08 Connection Guide

Software Setup - The Fun Begins

Time to make this thing actually work! First, let’s get your system ready:

# Update your system because why not
sudo apt update && sudo apt upgrade -y

# Install Python stuff we'll need
sudo apt install python3-pip python3-venv git -y

Installing My Python Script

Instead of wrestling with raw Modbus commands like some masochist, let’s use my pre-built script:

# Clone the repo
git clone https://github.com/CalmWookie/R4DCB08-Python.git
cd R4DCB08-Python

# Create a virtual environment (because Python dependency hell is real)
python3 -m venv .venv
source .venv/bin/activate  # Linux/macOS
# or .venv\Scripts\activate for Windows folks

# Install the requirements
pip install -r requirement.txt

Testing the Connection

Let’s see if this thing actually works! First, find your USB device:

# Linux/macOS - usually shows up as ttyUSB0 or similar
ls /dev/ttyUSB*
# or sometimes (for Pi Zero with USB OTG)
ls /dev/ttyACM*

# Windows users, check Device Manager for COM ports

Now test the basic connection:

# Read all temperatures (replace /dev/ttyUSB0 with your actual port)
python r4dcb08_cli.py rtu --port /dev/ttyUSB0 --address 1 read-all

If you see temperature readings, congratulations! You’re not completely hopeless. If you see errors, keep reading the troubleshooting section.

Reading Temperatures Like a Boss

Here’s where the magic happens. My script makes it stupidly easy to read temperatures:

Read All Sensors at Once

python r4dcb08_cli.py rtu --port /dev/ttyUSB0 --address 1 read-all

Output looks like this:

R4DCB08 Temperature Readings:
-----------------------------------
Channel 0: 22.5°C
Channel 1: 23.1°C
Channel 2: No sensor
Channel 3: 21.8°C
Channel 4: No sensor
Channel 5: No sensor
Channel 6: No sensor  
Channel 7: No sensor

Read Just One Sensor

# Read channel 0 (first sensor)
python r4dcb08_cli.py rtu --port /dev/ttyUSB0 read-channel 0

Different Device Address?

If your R4DCB08 has a different Modbus address (default is 1):

python r4dcb08_cli.py rtu --port /dev/ttyUSB0 --address 5 read-all

TCP Instead of Serial?

Some RS485 converters support Ethernet. For those fancy setups:

python r4dcb08_cli.py tcp --host 192.168.1.100 read-all

Calibrating Your Sensors

Because Chinese sensors are… optimistic with their accuracy:

Check Current Calibrations

python r4dcb08_cli.py rtu --port /dev/ttyUSB0 read-corrections

Set a Correction Value

If your sensor is reading 2.1°C too high:

python r4dcb08_cli.py rtu --port /dev/ttyUSB0 set-correction 0 -2.1

Or if it’s reading too low, add a positive correction:

python r4dcb08_cli.py rtu --port /dev/ttyUSB0 set-correction 1 1.5

Troubleshooting (When Shit Hits the Fan)

“No Sensor” Readings

  • Check your DS18B20 connections
  • Verify power to the sensors (should see ~5V between VCC and GND)
  • Try connecting just one sensor first
  • Some sensors are just dead on arrival (AliExpress special)

Weird Temperature Values

  • Check your calibration corrections with read-corrections
  • Could be electromagnetic interference
  • Sensors might need time to stabilize

Common Error Messages and What They Actually Mean

  • “Failed to connect”: Your port path is wrong or permissions suck
  • “Modbus error”: Communication issue, check address and baud rate
  • “Channel must be 0-7”: You can’t count properly
  • “Correction must be between -327.6 and +327.6”: Your correction value is insane

Conclusion

And there you have it! You now have a proper RS485-based temperature monitoring system that doesn’t suck. The R4DCB08 is actually a pretty decent little module, and my Python script makes it dead simple to use.

This setup is way more reliable than 1-wire for longer distances, and you can daisy-chain multiple R4DCB08 modules if you need more than 8 sensors. Just give each one a different Modbus address.

Now go forth and monitor ALL THE TEMPERATURES! Your ADHD brain will thank you for having yet another system to obsess over.

Next up: I’m planning to integrate this with Home Assistant and maybe build a web dashboard. Because why stop at “good enough” when you can over-engineer everything?

Additional Resources