1-Wire bus wiring

Overview

1-Wire combines a communication protocol and a physical interface. It connects compatible devices over two or three wires, including temperature sensors and iButton identifiers. Wiren Board supports DS18B20 digital temperature sensors.

Topology and capacitance

A linear bus is recommended. The source distinguishes a linear topology with branches shorter than 3 m and a stubbed topology with branches longer than 3 m. Star networks are not recommended: branch impedance discontinuities and reflected signals make reliable operation difficult.

Total bus capacitance and the pull-up resistance determine the RC rise time. Excessively slow recovery to logic high causes communication errors. Cable length and the number of sensors contribute most to capacitance.

Interference

Keep the bus away from power cables, motors, variable-frequency drives and switching power supplies. Cross power wiring at right angles. Shielding can reduce interference but increases bus capacitance. Connect the shield to GND at the master end only.

Wiren Board wiring recommendations

• The interface has an internal 3 kΩ passive pull-up between DATA and VCC; no external pull-up is required.
• Use a linear or stubbed bus and a total capacitive load no greater than 5 nF.
• Use UTP Cat.5e or better. The source specifies mutual capacitance up to 5.6 nF per 100 m and reports stable operation of one DS18B20 on 100 m of copper Cat.5e cable. Treat this as a reported example alongside the total-capacitance recommendation.
• Each DS18B20 adds approximately 0.15 nF, equivalent to about 3 m of cable.
• Use one twisted pair for DATA/GND and a second for VCC/GND. Join both GND conductors.
• Use three-wire sensor connections: +5 V, GND and DATA.

Supported Wiren Board devices include controllers 6, 7 and 8, WBE2-I-1-WIRE, WB-M1W2 v.3 and WB-MS v.2. Follow the particular device manual for terminal assignment and channel mode.