OpenBSD onewire

Introduction

I recently ran into a situation that called for some environmental monitoring
of some random things on my home property, and had long thought about playing
with Dallas Semiconductor "onewire" devices to do this: specifically monitoring
temperature.

Software Implementation

Conveniently, my home router (a Soekris net4801 runs OpenBSD 4.6,
which supports some of these devices wonderfully, and in a very convenient manner.

I opted to use a USB adapter (DS9490R) with some DS18S20 sensors.
The USB adapter attaches happily as uow(4) and automatically scans the
attached onewire(4) bus for devices.

These choices made this project very simple..

I also wrote a few custom scripts using the Bourne shell and Ruby to do things
with the data that the sysctl(8) interface provides me: I mainly graph the data
using rrdtool for trending and analysis.

Hardware Implementation

I used standard cat5e cable, which I already had plenty of around my house
(I'm a net admin, what can I say..) and RJ45 ends and mod jacks/wall boxes
due to their simplicity and convenience.

The cabling is simple, but involves some soldering to the sensors themselves.
There are 3 pins on a sensor: GND, DQ, and VDD: in my case, I actively use only
2 of them: GND, DQ. VDD is simply jumpered to GND because I'm using them in
"parasitic power mode", which means they draw power from the bus and store it
locally for later use. I used the blue and white-blue pair out of the cat5e,
and consistantly wired the white-blue to GND and blue to DQ as a convention.
I wired all of my sensors in a daisy-chain fashion because it works well for
this project and the layout of my onewire network.

Parts List (examples)

Required

• DS9490R-A USB 1wire Adapter - 1 of these per installation
• DS18S20 Temp Sensor - N of these
• As many feet of cat5e, cat3, thermostat wire, or any suitable 2-3 contact copper media (I use cat5e)

Optional

To make the installation pretty, and easier to maintain, I also use the following, at significant additional cost:

• Surface mount 2-mod boxes - N of these, that is: 1 2port box per sensor. Mine are a little different, this is just an example.
• RJ45 keystone modular jacks - N*2 of these, that is: 2 per sensor.
• RJ45 8P8C male connectors - N*2 of these, that is: 2 per sensor.

Code

I'll later make my code available for download, but I don't have time right now.

Graphs

Some of my example graphs can currently be found here.
No guarantees that they'll stay available at this point.