1-Wire: One Pair, Dozens of Temperature Sensors
1-Wire turns a single twisted pair into a temperature-sensing backbone for boiler rooms, manifolds, server racks and HVAC ducts — no home-run cable per sensor, no per-device configuration.
How the bus actually works
Two wires, sometimes one
Every 1-Wire device needs a data line and a common GND. A third Vdd wire is optional — many DS18B20 sensors run in parasitic mode, drawing power from the data line itself between pulses.
Factory-burned ROM ID
Each device carries a unique 64-bit ROM ID — 8-bit family code, serial number and CRC — burned in at the factory. That's what lets dozens of sensors share the same pair without manual address configuration.
One master, sequential polling
A single bus master (controller or gateway) drives all communication. It addresses each device by ROM ID and polls it in turn — devices never initiate; there's no bus contention to manage.
CAT5 does the wiring
CAT5/CAT5e is the common practical choice: one pair for data and ground, the second pair free for a dedicated Vdd feed if you skip parasitic power on longer runs.
What matters when you spec it
Factory ROM ID per device
Unique address burned in at manufacture — the reason a bus master can tell dozens of DS18B20s apart on one shared pair without configuring a single one of them.
Sensing bus, not a control bus
1-Wire is built for many slow, low-stakes measurement points — mainly temperature and ID reads. For fast or safety-critical actuation, KNX or Modbus are the right tool.
Two power modes
Run a dedicated Vdd wire for a straightforward, robust install, or use parasitic power to simplify cabling — the tradeoff is sensitivity on longer, busier segments.
Bus or star, both work
Installers run both linear (bus) and star topologies in practice. Reliable reach and device count depend on cable length, gauge, topology shape and pull-up resistor quality — not a fixed spec number.
iButton for access alongside sensing
The same ROM ID mechanism that addresses DS18B20 sensors also identifies DS1990/iButton keys, so a site can mix temperature points and access tags on related infrastructure.
Talks to Home Assistant and Loxone
A USB or network 1-Wire bus master/gateway reads devices by ROM ID and hands the values to your automation platform — no proprietary bridge required.
What we cover
Engineering support for integrators evaluating or deploying 1-Wire temperature sensing.
- {'t': 'Feasibility & topology review', 'd': "Assess whether bus or star topology fits your building's cable routes, and where parasitic power is safe to use versus where a Vdd wire is worth the extra conductor."}
- {'t': 'Cabling specification', 'd': 'CAT5/CAT5e pair allocation, GND continuity checks and pull-up resistor sizing guidance for the run lengths and device density on your project.'}
- {'t': 'Sensor & ROM ID planning', 'd': 'DS18B20 placement across boiler rooms, manifolds, server racks and HVAC ducts, with a ROM ID inventory so commissioning matches sensors to locations.'}
- {'t': 'Bus master / gateway integration', 'd': 'Selection and configuration notes for connecting your 1-Wire bus master to Home Assistant, Loxone or another automation platform.'}
- {'t': 'Commissioning & documentation', 'd': 'As-built wiring diagrams, ROM ID-to-location mapping and a handover pack your maintenance team can actually use.'}
Frequently asked questions
How many DS18B20 sensors can one 1-Wire bus carry?
There's no fixed number — it depends on cable length, wire gauge, topology and the quality of your bus master and pull-up resistor. In practice, well-wired runs comfortably carry dozens of sensors; we size each bus to the actual site rather than quoting a spec-sheet figure.
Do I need a separate power wire, or can I use parasitic power?
Both work. Parasitic power (drawn from the data line itself) simplifies cabling since you skip the third wire, but it's more sensitive on longer or busier segments with many devices active at once. A dedicated Vdd wire, easy to add with CAT5's spare pair, is the more robust choice for demanding runs.
Is 1-Wire suitable for anything beyond temperature?
Yes — the same ROM ID addressing scheme is used by iButton/DS1990 keys for access control. But 1-Wire is a sensing bus for many slow measurement points, not a control bus; for fast or safety-critical signals, use KNX, Modbus or another dedicated control protocol.
Can I mix bus (linear) and star wiring on the same installation?
Both topologies are used in practice, and mixing sections is common in real buildings. What matters is total cable length, wiring quality and pull-up sizing at the master — that's what we review during the feasibility stage.
How does 1-Wire integrate with Home Assistant or Loxone?
Through a bus master/gateway device — typically a USB or network 1-Wire adapter — that reads each sensor by its ROM ID and exposes the values to the automation platform. No proprietary bridge is needed.
Planning a multi-point temperature bus?
Talk to our engineers about topology, cabling and gateway integration before you pull cable.