TemperatureV2

TemperatureV2

A POE powered ethernet temperature sensor with two probes.

I wanted to be able to monitor temperatures in various locations in my server rooms. Most products on the market were designed around having a head unit that you plug probes into. This doesn't work for me since the locations I want to monitor have a fair bit of distance between them. My solution is a POE powered unit with two attached sensors. I can put them anywhere without concerning myself with power availability.

Hardware

The system is based on an Adafruit Feather M0 Basic paired with a Silicognition PoE FeatherWing and two DS18B20 sensors on leads.

The setup is extremely simple. The FeatherWing gets attached to the M0, including the SDA and SCL pins. A single 4.7k resistor ties pin 5 or 6 to 3v3 and the data lead of both sensors.

This setup costs about $50, and even spending that on each unit I want to deploy, it still costs less than the commercial solutions.

Enclosure

To protect the unit we need an enclosure. The enclosure needs to be able to release about 1W of heat from the PoE components.

The enclosure included can easily accomplish that and exposes the USB port for reprogramming (or external power). The battery connector is not exposed in this enclosure.

Software

Based on some Arduino libraries, the included software manages the sensors and serves up a very basic webpage.

You may notice this is V2. V1 was considerably larger based on an Arduino. It produced more heat, and the firmware had to be altered for each unit to program the MAC address. Since the FeatherWing includes a globally unique MAC address, we don't need to change the firmware for each unit.

Since this is V2, I wanted to maintain backwards compatibility with V1. That's not hard, it just means that the root request "/" can only return temperatures T1 and T2. I added a second endpoint "/v" which returns the MAC address (serial number) and version of the software in addition to the temperatures.

In production, you'll want to setup DHCP reservations for the sensors so that they are always where you expect.

Bugs

None that I know of. However, you cannot power cycle the DS18B20 sensors rapidly. Because of that, if the unit loses power for less than a second it may not be able to locate one or both of the sensors when it boots back up. In production this shouldn't happen, but I was able to produce the issue several times during development by quickly unplugging and plugging back in to reset the hardware.

License

Copyright (C) 2021 Beau Barker

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.