Chapter 4 Sensors in WildlifeSystems

The WildlifeSystems platform comes with support for some popular existing environmental sensors, although there are many on the market and the range available is subject to constant change. The modular nature of WildlifeSystems allows for new sensors to be easily integrated if the need arises.

As many physical packages contain multiple sensors (e.g. the supported BME680 can monitor temperature, humidity, air pressure and air quality) there is a conceptual difference between a “device” and the one or more sensors on a device.

4.1 Devices included in the base system

The Raspberry Pi does not come with environmental sensors, however there are several onboard sensors that are used to monitor the operation of the hardware, to prevent crucial components from overheating, including the temperature of the CPU and GPU chips. WildlifeSystems provides access to these sensors through the sensor-onboard package, as well as providing some software sensors that report the free memory and free SD storage available. These can be useful for detecting and resolving possible issues on a sensor node before a serious problem arises.

4.2 Installing sensor support

Support for sensors is installed as part of the node installation process, however it is possible to install the sensor-control abstraction layer onto any Raspberry Pi system using the command below.

wget -O - | sudo bash

This will install the sensor-control and sensor-onboard scripts into the system, as well as installing a small of number of supporting packages if they are not already installed.

4.3 Reading data from a device

The sensor read command, sr, can be used to list the available devices on a given sensor.

sr onboard list

The sensor read command, sr, can also be used to read data from a named sensor. Not specifying a sensor is equivalent to reading all sensors on that device (i.e. using the wildcard”*“).

sr onboard
sr onboard *
sr onboard onboard_gpu

This will give a JSON string listing information about each sensor (or just the specified sensor), and the current reading. This information can be presented in a more human readable form by piping the output to the program jq, a command line JSON processor.

sr onboard | jq

4.4 The sensor reading process

The sensor reading process in WildlifeSystems has five steps.

  1. The sr command identifies which device script to route the request to.

  2. The sensor script calls the sc-prototype script to obtain a template (“prototype”) of the JSON request.

  3. The sensor script accesses the relevant sensor(s) and populates the values in a template for each sensor reading, before returning a JSON array of populated readings to sr.

  4. The sr script populates additional information for each reading, providing the node_id and a timestamp for each.

  5. sr returns the finalised JSON array to the user.

4.5 Installing new sensors