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1-wire communication interface

Picture of 1-wire communication interface
What is 1-Wire technology ?

The basis of 1-Wire technology is a serial protocol using a single data line plus ground reference for communication. A 1-Wire master initiates and controls the communication with one or more 1-Wire slave devices on the 1-Wire bus. Each 1-Wire slave device has a unique, unalterable, factory-programmed, 64-bit ID (identification number), which serves as device address on the 1-Wire bus. The 8-bit family code, a subset of the 64-bit ID, identifies the device type and functionality. Typically, 1-Wire slave devices operate over the voltage range of 2.8V (min) to 5.25V (max). Most 1-Wire devices have no pin for power supply; they take their energy from the 1-Wire bus (parasitic supply).

More about 1-Wire technology may be found on Maxim IC web pages.

1-Wire master communication interface

This instructable will show how to implement and use basic serial 1-Wire master communication interface like one show on picture (link).


 
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Step 1: PCB for project

For this instructable we will use 1-Wire Comm V1.00 PCB board from Dubi .

This very modular PCB have two parts :
  • 1-wire serial communication interface
  • voltage regulator parts (using 78xx IC)

Pictures show both side of PCB.
PCB give possibility to use SMD or normal scale elements for accomplish functionality on most parts, and different  connection options.

In some small number cases you may use 1-Wire device without any additional power supply. How ever when you try to do just little complicate things with more 1-Wire devices or with longer communication lines (wires)  you will need to supply 1-Wire device with proper power.


kelseymh3 years ago
I probably need to read the technical documents, but you might be able to answer this question more quickly.  How does this system avoid ground-loop noise, or level shifting due to different grounds?  Most systems have their non-power circuits "grounded" internally rather than to earth, so how do you guarantee the same ground level at each end?
Most of these devices are battery monitors, memmory, and temp sensors so its all stuff that uses little power and short wire runs. Levelshifting and ground loops are not an issue.
.  It's not really just one wire - all that means is that it's a single-ended not a differential signal. RXD (pin 2) provides the "common ground".
.  But I'm not much better with electronics than I am with higher Mathematics. ;)
"all that means is that it's a single-ended not a differential signal" sorry but that is not true.

SPI and i2c are single ended and multi wire...

1 wire devices use 1 wire for power which is level shifted to get the data in and a ground...

At the current draw of these chips in the mA range and the resistance of the wire being mΩs the voltage drop should be in the 20mv or less range so no worries about grounds not beinng exactily equal... But it dosent matter becaues of the wide supply range the chip will work. I would be more worried about trying to charge the capacitence of a long line directly from a uC io pin. RS232 version here is probably fine for any length cable.
dpenezic (author)  kelseymh3 years ago
In real live it is 2 wire, how ever it is defacto standard to use UTP cable to connect devices which provide more flexibility and noise reduction.
omnibot3 years ago
Nice one.
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