1-Wire Hub
From PhotoVoltaic Logger new generation
Abstract
I monitor here 3 1-Wire temperature sensors. (DS18B20 datasheet)
As I looked at commercial solutions and their prices, I decided to construct my own 1-Wire hub.
Sensors and network
The DS18B20 temperature sensor can be powered by an external supply on the VDD pin, or it can operate in "parasite power" mode, which allows the DS18B20 to function without a local external supply.
- In normal mode, each sensor is connected between a power line (VDD pin 3) and ground (GND pin 1), and the data output (DQ pin 2) connects to a third, data, line. The data output is a 3-state or open-drain port (DQ pin 2) and a 4.7 kΩ pull-up resistor to the power line is required.
- Parasite power mode requires both DS18B20 GND (pin 1) and VDD (pin 3) to be connected to ground. The DQ pin (pin 2 - the middle pin) is the data/parasite power line. The data line requires also a pull-up resistor of 4.7 kΩ connected to +5 V.
http://openenergymonitor.org/emon/buildingblocks/DS18B20-temperature-sensing
http://www.hacktronics.com/Tutorials/arduino-1-wire-tutorial.html
http://datasheets.maximintegrated.com/en/ds/DS18S20.pdf
If you have long 1-Wire network runs and are having problems with glitches you should add a Schottky diode to the end of your network. Typically a 1N5817 diode reverse biased across sensors will achieve this. Solder the side with the stripe to data output (DQ pin 2) and the other side to ground (GND pin 1) of the DS18S20.
Build
Therefor I had to decide, how to connect them to the sever.
- Simple to build > breadboard platine
- Stable > normal mode
- Linear topology (according to this guidelines) > more stable than star topologies
Use a bit thicker telephone cable: J-Y(St)Y 2x2x0,8
