Information about the 1-wire bus, area of application, benefits, installation

. Updated on 1 July 2020

1-Wire is a powerful bus system that is particularly appreciated for its simple design and energy saving. energy saving. The bus participants are controlled by a master. All slaves are equipped with individual addresses ex works and are fully calibrated. There are no other system devices, no complex rules for addressing or topology have to be observed, and there is absolutely nothing to parameterise. It couldn't be simpler. Just connect all slaves to the same line (2 or 3 wires), switch on the server, done.

Efficient, compact & Precise:
No other bus system requires so little energy. On average, a current of only one millionth of an ampere is required to operate a 1-wire temperature sensor. Because of this extremely low energy consumption and the use of shielded cables, 1-Wire is also practically completely radiation-free. Thus, 1-Wire enables a cost-effective and extraordinarily energy-efficient design, allows high precision without disturbing waste heat as well as a very compact design of the components.

Simple clients instead of complex software:
There are hardly any modern products left that are not equipped with microprocessors and local software. Even for devices with clear functionality such as clocks, headphones, lamps and speakers, a regular software update becomes necessary. In a smarthome, there are usually between fifty and three hundred devices installed with updateable software. With an increasing tendency. Plus consumer electronics devices and modern household appliances. The basic update option tempts manufacturers to sell products that are not fully developed. In the end, every day some other of the installed products needs an update. These frequent changes to the system make lasting stability difficult. The incompatibilities that sometimes arise as a result entail renewed and further updates. The owner becomes the system administrator of his technology - instead of enjoying the comfort.
Such tasks do not exist with our 1-Wire products. There is no software in our 1-Wire sensors and actuators that would require updates. The protocol and the functions are cast firmly in silicone. This is ultra-stable, unchangeable and works forever. Simple, robust and stable electronics for the task at hand - no frills, no updates, no incompatibilities. A 1-Wire bus runs for several decades. Without any administration.

Since 15 years, over 250 million devices:
1-Wire sensors and actuators have been in use for almost 20 years and are now installed in well over 750 million devices, where they are used to measure temperature, humidity, voltages, charge monitoring of battery packs, contact monitoring, as flash memory, as well as for anti-counterfeiting of electronic devices.

We are the global market leader for 1-Wire sensors and bus masters:
We have been offering sensors, actuators, bus masters and servers based on 1-Wire since 2009. Since the beginning, we have developed several hundred sensor and actuator variants for a wide variety of purposes and have thus achieved technological market leadership. Our multi-channel bus master PBM holds the world record for range and number of supported slaves. Our Plug'n'Play in the Timberwolf Server sets standards in the automated commissioning of new sensors / actuators. Our products are used in building automation, for plant monitoring in Industry, in products of our OEM customers, in research & education, in the laboratory, in the construction industry as well as in agriculture.

Why sensors / actuators based on 1-Wire and not KNX / Modbus / Profibus or why simplicity is important?
We are often asked why we have not developed our sensors on the basis of KNX, Modbus or Profibus:

Complex protocols like KNX, Modbus or Profibus require microprocessors in all devices. The development is complex, the certifications expensive, the costs high and the commissioning much more complex. In addition, complex protocols distributed in updateable microprocessors allow an installation to be vulnerable.

Modern building automation, the smart grid and Industry 4.0 increasingly require more sensors / actuators. However, what is also desired is the lowest possible energy consumption and the avoidance of security problems from complex, distributed software.
Simply designed products enable a shorter development time, lead to lower costs, allow significantly easier installation and commissioning, offer high stability and avoid follow-up costs.

In other words: Many of the sensors / actuators / ibutton solutions etc. we offer would not be cost-efficiently realisable without 1-Wire. No other bus standard allows these many designs and application possibilities. With our developments it became possible to equip a normal house with over one hundred sensors for less than 2,500 euros. Our customers enjoy comprehensive monitoring of ventilation and heating systems, precise control of temperatures from cold storage to sauna, measurement of local weather, frost protection, mould prevention, leakage monitoring, insulation monitoring (thermal), irrigation (soil moisture & valves) as well as regulation of the comfort of living spaces (temperature, air humidity, air quality and light).

Simplicity is an advantage you should take advantage of. Imagine installing dozens or hundreds of sensors / actuators and not having to calibrate any of them, assign addresses during commissioning or install updates. Just connect a bus master to the bus and all these 1-Wire slaves work as if by themselves. The server only needs an update when sensors of a new type are offered which you then also want to install. This is also very easy with the Timberwolf Server. Simply press the "Update" button and the update will be installed automatically. The previous configuration is of course retained.

Advantages 1-Wire:

Simple Simple:
   No programming necessary: Install, Connect, Done!
   Only one line for 20 - 200 devices / sensors / participants (depending on the type of bus master)
   Small sizes allow local installation and a truly decentralised bus system, thus saving on cabling

   Temperature sensor (depending on version): approx. 2 € – 40 €*
   Multisensors (for flush mounting): approx. 30 € – 60 €*
   Universal I/O: from approx. 5 €* per channel
   Standard Busmaster: from approx. 20 €*

   iButton: approx. 5 µW**
   Temperature sensors: approx. 5 µW**
   Universal I/O: approx. 0.5 mW**
   Multi-sensors (humidity / light): approx. 1.75 - 4 mW**
   Standard bus master: approx. 7.5 mW**
   Professional Busmaster: approx. 180 mW**
   Timberwolf Server (depending on version): approx. 2.5 - 12 W**

What do these values mean? The energy consumption of e.g. a temperature sensor is so low that you would have to operate it for about 770 years before the operating costs would amount to one (1) cent! A complete system (Busmaster, Timberwolf Server, several hundred sensors - except VOC) can be operated for about 10 to 15 € per year. Please keep this in mind when comparing different technologies. A house and its systems are planned for decades. Therefore, always extrapolate the energy costs for the operation of sensors etc. to 10 to 20 years.

*Prices incl. VAT plus shipping costs, as of June 2016, subject to change;
**(µ= micro = 1 / 1,000,000 = one millionth) , (m = milli = 1/1,000 = one thousandth)

Energy costs compared to KNX:
The low energy consumption of 1-Wire pays off especially when compared with bus systems whose devices have a higher energy consumption due to their principle. Let's compare the energy costs for hundreds of sensors in a building:
While one hundred 1-wire sensors (Temp, Multi, IO) cost less than one euro in electricity costs in ten years, one hundred KNX-based sensors (at least 1/4 watt each) would cause an electricity bill of approx. 1047 EUR in ten years. Due to the immense energy savings alone, 1-Wire components pay for themselves over their lifetime. Whereby a consideration of 10 years is rather short-sighted, because home control systems are planned and operated for much longer periods. Energy costs, even energy costs, even for very small components, can become quite significant, especially as these costs will rise disproportionately in the future.

The costs for the server are added, but since it also provides a number of other services for building automation, its energy costs should not be blamed solely on the 1-wire function. Our servers are also designed for extremely low energy consumption. Only between 2.5 and 5 watts are required. This is extremely low compared to other servers for building automation. Ask and extrapolate that to 15 to 20 years.

Basic structure of a 1-wire bus system:
The structure of a 1-Wire system is very simple
. 1. there is only one system device on the bus – the 1-Wire bus master. It supplies the bus and provides the signalling.
2. The sensors / actuators are connected to it. These are fed from the bus master.
3. The bus line is pulled from the bus master to the first sensor/actuator and from there to the next one. Like a Christmas tree chain.
4. a server controls the bus master(s) via drivers, controls the connected sensors / actuators and calculates the sensor values based on the characteristics.
5. all system components run on extra-low voltage ("SELV" = "Safety extra low Voltage"), so a small power supply unit with 12 / 24 V and 10 W is required.

Let's summarise this briefly: You need the 1-Wire sensors / actuators, a cable, one or more bus masters, a server and a small power supply unit (10 W) for everything.

The server for 1-Wire:
The 1-Wire system is a master-slave system. The slaves (sensors and actuators) are kept very simple. Only individual 1-Wire actuators have an automatic self-sufficient mode in case of a control failure. No digital system can do without a controller. With 1-Wire, this is located in the master, which consists of hardware and software. The hardware is the "bus master", the software for the entire system runs on a server, e.g. the Timberwolf Server.
The Timberwolf Server automatically recognises all connected bus masters and the 1-wire sensors / actuators connected to them. Some parameters can be set via a simple configuration interface (WebApp), such as the frequency of the measurements, recording of the values in databases for evaluations and forwarding to other bus systems such as KNX, Modbus, etc. The server also acts as a logger. The server also acts as a logger, database and gateway to other systems.
Furthermore, the server provides other functions and additional capabilities that have nothing directly to do with 1-Wire, but are very useful for service and maintenance of the entire building automation:
   Encrypted dial-in via VPN for access from the outside
   Calculation of logic functions and gateway to other components such as heating, KWL etc. (via plugin)
   Visualisation of all states of the building automation with e.g. the "CometVisu"
   Logging and analysis of all data packets on the KNX bus for troubleshooting
   Providing date and time ("timer") for the KNX bus
. Further features are described in the article description of the Timberwolf Server
Application range for 1-Wire

1-Wire is particularly suitable for sensor technology, (temperature measurement, battery monitoring, voltage, temperature, current flow), for control and signalling (push-button interface, window contact, smoke detector) as well as for identification through unique, unambiguous and unchangeable 64-bit serial numbers (access control, digital key board).

Offline sensors (iButton) are also available for use in food monitoring (e.g. Thermochron iButton) and in the agricultural sector as data loggers. Here, for example, air humidity and temperature are regularly logged internally by the iButtons autonomously (without a permanent "1-Wire bus connection") and this can be read out later via a 1-Wire bus master / host interface.

In the field of building automation, 1-Wire sensors are particularly interesting for the detection of temperature, air humidity, barometric pressure, air quality, ambient light, detection of window contacts etc. as well as for the continuous measurement of other environmental values, especially because of the very favourable price, the very simple wiring, the extremely low energy consumption.

Installation with 1-wire sensors:

1-Wire sensors already include complete evaluation and digitisation as well as the 1-Wire bus interface. In the case of the temperature sensors, all this is contained in a tiny TO-92 housing - or in the case of SMD components - even smaller.

Because of the digitalisation in the sensor element, there is no need for any calibration - not even because of the cable length. Moreover, with a tolerance of only +/- 0.5 °C, the sensors are much more precise than conventional PT100 or PT1000 sensors and their evaluation electronics with tolerances of mostly +/- 2 °C. In some switches with high waste heat for many LEDs, the deviations in temperature measurement are up to 8 Kelvin !
1-Wire Sensors
The connections of the sensors are connected to each other in the simplest way, e.g. with a simple two-wire ring cable from room to room (without electrically closing the ring). Due to the serial number contained in each sensor, a doubtless assignment to the measuring point is possible at any time.

The Busmaster / Hostadapter is connected at one point in this bus, which - when the sensors are connected "powered" - also provides the power supply (5 V) via an optional third wire and controls the communication on the bus (one-master / multi-slave).

As a rule, the sensors can supply their power requirements from the data line by means of an integrated capacitor ("parasitic power"), so that two cores are usually sufficient; in the case of greater power requirements or for an extended temperature range, additional cores with 5 V and / or 12 V may be necessary. Please refer to the information on the respective units.

Note: All 1-Wire temperature sensors, the multi-sensors (but not the VOC) as well as the multi-IO (2-fold, 4-fold 6-fold) can be operated with a parasitic power supply (2 wires) without any problems. The respective limits depend on the bus master. Please refer to our planning manual for this information. For the following products, a separate supply via 12 or 24 V (fourth wire) is necessary: VOC sensor, soil moisture sensor, 8-fold LED actuator and 4-fold valve actuator.

The price per sensor line with ready-made sensors is 32.44 EUR each for approx. 20 measuring points (incl. Timberwolf Server, Busmaster / Hostadapter and 20 cable temperature sensors). This comparison is actually insufficient, because it does not yet take into account the significantly enhanced capabilities available with the Timberwolf Server.

Topology / Recommendations for 1-Wire Bus:

The optimal function of the 1-Wire bus is decisively determined by three parameters:

1. selection of the correct busmaster and its control by the software. The latter is done optimally for you by the Timberwolf Server.
2. number of sensors and the sum of the length of all wires.
3. and especially the topology used (bus, star, etc.).

Tabular overview of the different topologies for 1-wire bus:

1-Wire installation as a line with branches

Tree structure

1-Wire Tree Structure
Yes, 50 - 100m total length and 10 - 20 sensorsLimited, only for small installations
As a bus with short branches (a few metres)

Tree structure, short branches

1-Wire Tree Structure, Short Branches
Yes, up to 100m possible.Yes, almost optimal length extension possible.
When the "branches" are dispensed with, all sensors hang one behind the other


1-Wire Line
Yes, up to 150m possible.Yes, optimal installation, maximum range.
All sensor lines are brought together at one point


1-Wire Star
Yes, up to 100m total length possible <= 10 sensors.Limited, only for small installations
When one end is connected to the beginning a

=> ring

1-Wire Star
NoNo, no function

Note regarding this table: The above information refers to compliance with the recommendations given further below regarding installation cables, wire assignment, shielding and distance from interfering radiation
Mixed structures: These topologies can also be mixed within certain limits. With regard to the length recommendations and max. number of sensors, however, those of the topology involved with the lowest specifications should then be observed. Example: If, for example, sensors are connected in lines and these lines are in turn connected in a star, we recommend a total length of 100m and a total number of 20 sensors not to be exceeded.

Restrictions when using Parasitic Power: When connecting the 1-wire sensors with "Parasitic Power", as described below, we recommend a maximum length of 200m and no more than 40 sensors - per channel - when using the Professional Busmaster PBM. Please note that when using Parasitic Power, the maximum measurable temperature is about 85 °C (instead of up to 125 °C when supplied with 5V).

Per 1-Wire Bus: These specifications apply per 1-Wire bus, but - depending on the host master / gateway - several buses can also be connected to one server.

Multiple bus masters: At the Timberwolf Server theoretically about 80 bus masters with 20 sensors each can be connected. Up to 15 busmasters / host interfaces we have also tested this positively. DS9490R 1-Wire USB Adapter

Further information: For further information please consult our planning manual

Installation variant 1-wire sensors with "Parasitic Power" (recommended):

1-Wire Parasitic Power

Note: This schematic sketch does not reflect the exact connection assignment / pin assignment of a specific sensor. Please refer to the respective data sheet.

Please check on the basis of the manufacturer's specifications / data sheets whether a 1-wire sensor is suitable for parasitic power supply via the DATA data line (also referred to as DQ). This is not always the case, especially with multi-sensors (temperature, humidity, pressure, ambient light) or IO boards from other manufacturers. This connection variant is usually referred to as "parasitic power". All our temperature sensors are basically suitable for this. Likewise, our multi-sensor (without VOC) and the multi-IOs can be connected parasitically.

In parasitic operation, only two wires are connected to the bus master at the sensor: GND and DATA (DQ).

Important notes on configuration: For sensors that only contain the sensor element DS18B20 without further electronics (i.e. the sleeve sensors), the following applies: The VDD connection of the sensor element must be connected to GND so that the sensor element is configured for parasitic supply. This should be done directly at the sensor. Please note: The jumper described above is only to be made on the sensor side; under no circumstances may it include the output VDD of the bus master! In the case of sensor products with a printed circuit board, such as the Multisensor, the Multi-IO etc., such bridges must NOT be attached to the connections. With these products, the switchover to parasitic supply is automatic. Please refer to the respective data sheet.

Explanation: With parasitic power supply, the sensor draws the operating energy from the DATA line and stores it temporarily in a capacitor during the HIGH phases. To ensure that a sufficiently large current can be supplied, especially for charging the capacitor at high level, both the correct control by the software and a bus master / host adapter with strong pull-up are required. The software included in the Timberwolf Server as well as all 1-wire bus masters available in our shop support this!

Note for parasitic operation:
- Only for sensors whose data sheet provides for this operation (temperature / humidity)
- Only if the software of the host master and the bus master also support this!
- Total cable length per bus: <=100m
- Number of sensors per bus: <=20
- Restricted measuring range for temperature sensors: max: approx. 85°C
- For sensors that only contain the sensor element DS18B20, the following usually applies: Pin 'VDD' of the sensor must be connected to 'GND' on the sensor side for configuration of the parasitic operating mode! No bridges are necessary for multi-sensors or multi-IO from our company. Please always refer to the respective data sheet.

We recommend the parasitic installation variant because of the significantly lower cabling effort and the lower probability of incorrect wiring. This is also usually the easiest variant to use retroactively, as two twisted wires are often still free in existing telephone or KNX cabling. 1-Wire is SELV and may therefore be used together with other SELV applications such as KNX in the same line (but on different cores).

Recommendation for new planning: In order to keep open all possibilities for later expansion for sensors that require an additional power supply (e.g. air quality sensor VOC or Multi-IO for LEDs), we recommend, despite predominantly possible parasitic connection of the temperature sensors with only two wires, to lay and provide at least 3-4 wires for 1-Wire as far as possible.

Installation variant with 1-wire sensors and power supply through the bus master:
1-Wire installation with separate power supply
Note: This schematic sketch does not reflect the pin assignment of a specific sensor. Please refer exclusively to the respective data sheet!

All temperature sensors and the Advanced Multisensor may also be supplied with 5 V from the bus master instead of a parasitic supply. The bus master can supply a total current of up to 25 mA.

Note: Please be sure to observe the data sheets for the respective sensor.

Installation variant with separate power supply through external power supply units
When using other sensors with higher current consumption (e.g. Multisensor with air quality sensor VOC or Multi-IO with connected LEDs & relays), the power supply must be provided by separate power supply units with 5 V or 12 V.

Here, only GND and DATA are connected to the bus master. The power supplies for 5 V and / or 12 V must be connected to the power supply unit. Important: GND of the power supply unit must be connected to GND of the bus master. Please refer to our planning manual.

Note: Please be sure to observe the data sheets for the respective sensor.

Mixed operation: All installation variants can also be operated mixed on the same bus. For the parasitically operated sensors, only VDD is connected to GND on the sensor side (if necessary and permissible).

Cables / Wire assignment:

For most applications, the normal telecommunications installation cable ("telephone cable") J-Y(ST)Y 2x2x0.8 or a KNX installation cable is best suited.

Note on the diameter or cross-section of the cores: Unfortunately, the specifications for diameter (mm) or cross-section (mm²) of cores are often confused with each other by wholesalers and retailers. Particularly in the shop for the golden 'C', the information was wrong in half of the checked articles. We therefore strongly recommend that you always check the original data sheets of the manufacturers.

Essentially, three specifications can be found: For thinner cores, it is often common to state the core diameter in mm. Rarer is the specification of the cross-section in mm² or AWG. To determine the cross-section from the AWG number, it is necessary to use a table.

The cross-section is the cut surface of a wire. The current conduction takes place via this cross-section. A double cross-section here means a halving of the electrical resistance of a line and thus also a halving of the losses.

We recommend 0.8 mm diameter: Although cables with a core diameter of 0.6 mm are more common and "usual" than those with 0.8 mm, the cross-section of the 0.8 with almost 0.5 mm² is twice as large as that of the 0.6 mm with a cross-section of only 0.25 mm². This means that the loop resistance is only half and the voltage drop is also half. Especially for sensors with higher current consumption such as multi-sensors with VOC or multi-IO with LED control, a wire diameter of 0.8 mm is highly recommended.

Data cables such as CAT 5 / 6 / 8 are more than suitable for 1-Wire in terms of noise immunity and transmission quality, but the cross-section is usually only 0.2 mm² (AWG 24) and thus only about 40 % of the cross-section of 0.5 mm² (diameter 0.8 mm) recommended by us.
For normal temperature and multisensors, a cross-section of 0.2 mm² is quite sufficient for lengths up to 100 m and with 20 sensors, but this small cross-section leads to line losses with sensors with comparatively high current consumption (especially with several of them on one bus) such as multisensors with VOC (with approx. 35 mA compared to a multisensor without VOC with approx. 500 uA). Therefore, we recommend a cross-section of 0.5 mm² (diameter 0.8 mm) for lengths up to 400 m with 80 to 100 sensors.

ImPORTANT note on wire assignment: For maximum interference immunity, a twisted pair of wires must be used for the signals 'DATA' (also referred to as 'DQ' or '1W') and 'GND' together! (for J-Y(St)Y these are usually the combination rt/sw or ge/ws)

- Fixed-wired: Any in flush-mounted / surface-mounted boxes with e.g. (micro)-plug-in terminals or in distribution on terminal blocks or LSA+ strip.

- Pluggable: If detachable plug connections are preferred: With commercially available two- or four-pair twisted pair cable from category 5 laid on panels and hubs with RJ12 / RJ45 plugs.

Belegung der Wires bei Nutzung mit Stecker

(e.g. J-Y(St)Y)
(WireGate sensors)
6/6 male
8/8 male
Black (sw)BlueGround (GND)45
Red (rt)WhiteData34
Yellow (ge)BlackVDD (+5 VDC)12

RJ-12 connector
(from front)
RJ-45 connector
(from front)
Pinout 1-Wire RJ12 Pinout 1-Wire RJ45 

Practical notes:

Please do not connect the shield and shunt wire and do not connect through at the terminal points.

We recommend connecting the sensors one after the other and starting a search run on the Timberwolf Server in each case and making the assignment (name / designation).

WireGate Label Assembled 1-Wire sensors purchased from us are equipped with a label that also contains the serial number. We suggest that you make a note of this label during installation so that you can later specify the installation location of the sensor in the user interface of the 1-Wire server.

Advantages 1-Wire:
  Inexpensive sensors and gateways / adapters
  Easy to wire (bus), comparable to other bus systems (KNX, DALI, etc.)
  High accuracy (for temperature sensors)
  No falsification of measured values due to cable length/noise influences (digital transmission of measured values from sensor to bus master/host adapter)
  Easy assignment as each sensor has a unique serial number.

   "Relatively" slow when reading out (between 100 and 750ms depending on resolution 9 - 12 bits), but should be completely negligible in practice.
  Not all topologies are possible for line lengths >100 m.