Use AM2315 for temperatures below 0°C

am2315-temp-humidity-sensorIn an IoT node I use an AM2315 sensor to measure temperature and humidity. This sensor can be connected via   I2C bus to a NodeMCU module. The results of these periodic measurements are presented here.

On my location these days we had negative temperature on the Celsius scale for the first time in this autumn.

What happened? I had to see wrong temperatures in my graphs.

I looked for the root cause and found that in the used library AM2315.lua the range below 0°C was not handled. The MSB of the temperature value is set in the case of negative temperatures. Therefore I masked this bit and if set the value is multiplied by -1. If you use customized firmware the bit module must be included.

Here are the modified lines for AM2315.lua:

h = string.byte(b[3]) * 256 + string.byte(b[4]) --humidity
h = h / 10
-- MSB is set for negative temperature
t = bit.band(string.byte(b[5]), 127) * 256 + string.byte(b[6]) --temperature
t = t / 10
if bit.isset(string.byte(b[5]), 7) then t = -1 * t end

You will find these modifications on https://github.com/tectiv3/am2315-lua, now.

Finally, here is a temperature graph from today. Winter is coming now 😉

negtemp

Use AM2315 for temperatures below 0°C

Last Phase

CoverThe analyst firm Gartner says that by 2020 there will be over 26 billion connected devices…that’s a lot of connections (some even estimate this number to be much higher, over 100 billion).

The IoT is a giant network of connected “things” (which also includes people).  The relationship will be between people-people, people-things, and things-things. The new rule for the future is going to be, “anything that can be connected, will be connected.”

In this book I will consider the frontend of the IoT – the so-called IoT node. This IoT node is connected to sensors and actors and to the network. Our IoT node here uses WLAN connectivity to the network by which it is very easy to integrate it in an existing office or home network.

This task can be fulfilled by a lot of wireless network capable microcontrollers as Arduino, Raspberry Pi, Beagle Bone and further more equipped with a Wifi device. But the use of such complex devices is not in focus here. Our goal is to use a very cheap device to build a compact IoT node.

The title of this book defines our goal – building an IoT Node for less than $ 15. A listing of expecting costs for the various components is given in the IoT Node Costs.

The ESP8266 microcontroller is the base for this journey.

The book is scheduled to appear in the autumn 2015. Here is the table of content. If you are interested in more details please leave a replay.

Last Phase