1-Wire Temperature Sensors

In each room/space in our house we are testing the installation of DS1920 1-Wire temperature sensors. These are cheap and accurate wired devices.

These are easy to write code for and here is sample code in the 1-Wire API examples. Our code measures temperatures very frequently and each device is configured to measure to the nearest 0.1½C. We only log changes over 0.3½C though as this approach results in logging significantly less data. To make plotting of data easier I also forcibly log the values at the start of each day and at the end of each day, i.e. the start and end of each log file.

Wall Mounting

Though harder to achieve in an existing home, we have assumed that the temperature sensors will be wired and wall mounted. To achieve the fairly flush, low-profile fitting that we want, this then assumes some kind of mounting box in the wall. This needs to be fairly small but, big enought to expose two Cat5 cables through. It also needs to be air tight and capable of being insulated so that the temperature sensor is not subjected to cold air from the wall spaces.

Initially we looked at these 'thimble' housings but ruled them out because of their small size and there is no obvious way to fix them to the wall. They do come in various materials and colours though.

We also looked at these dome housings but, they have many of the same problems.

Conclusions

It is rarely practical to install wired sensors in every location required in your existing home. The complexity of running long cable lengths and the logistics and access can make it very difficult. It makes a lot more sense in a new build though. The Dallas 1-Wire network technology is reliable but, longer cable lengths can cause issues.

The resolution and accuracy of 1-Wire sensors is good. It is very hard to match with other technologies and many of these cost considerably more. Fortunately, there are many other devices and technologies such as Z-Wave that allow you to also use these DS1820 sensors on wireless mesh networks. This adds significantly to the cost though.

A temperature sensor in every room is a fundamental requirement of our planned climate control system though.

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