Table of contents
1. ARDU TEMP #1 - The project: building a battery powered temperature beacon
2. ARDU TEMP #2 -The kit, Arduino, NodeMCU, ThingSpeak
3. ARDU TEMP #3 - Testing the beacon
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Introduction
Over the past few years I’ve worked on a number of projects (consulting, sensor boards hardware design and software integration) for industrial automation and IoT custom/bespoke applications. Most of these projects were for small businesses (greenhouse, roasting coffee and nuts factories, various workshops, etc…). In my designs, I use sensors to monitor temperature, humidity, CO2 or other gases in order to control (e.g. switch on/off) various pieces of equipment using network connected switches.
A general automation framework
I’ve recently started working on a personal open source software project that aims to make automation accessible to a DIY user. My main interest revolves around greenhouse automation (irrigation, temperature and light control), however the technology bricks I am developing should be flexible enough to allow development of any other type of automation application where a system collects sensor data and reports the measurements to a data logging platform which then takes appropriate action (e.g. reports, alarms, warnings) according to a set of predefined, configurable rules.
For the type of applications like the ones I have in mind, electric lines on premises are present and most of the time the site has at least one WiFi access point from which WiFi coverage can be extended using repeaters or mesh routers. This is the reason why I decided to use WiFi rather than Zigbee, Bluetooth LE or other similar radio technologies to connect end devices.
For collecting sensor data and relaying commands to networked switches, I decided to use NodeMCU https://en.wikipedia.org/wiki/NodeMCU because it checked all my boxes (inexpensive, small form factor, WiFi connectivity, enough GPIOs to connect sensors). Being able to program NodeMCU using Arduino IDE was also a big factor - taking into account how popular Arduino is.
For connected/networked switches as a means to turn on and off equipment (heaters, fans, irrigation pumps, etc…) I chose Sonoff WiFi Smart Switch https://sonoff.tech/. The ESP Easy firmware allows this type of switches to be controlled from the LAN rather than the closed, proprietary cloud platform. https://www.letscontrolit.com/wiki/index.php/ESPEasy#Loading_firmware
As an IoT platform I selected Thingspeak, an analytics platform service that allows IoT developers to store, visualise, and analyse live data streams on the cloud. It is open-source software and it facilitates data access, retrieval, and logging, with APIs for the hardware.
Using the components listed above to build an automation system, a DIY user should be able to easily configure the system to perform fairly complex tasks with minimal work. (simple Arduino IDE development on NodeMCU, text scripts on Sonoff, config work on Thingspeak.)
Interest in thermal switches
First, I would like to see if thermal switches can be used at voltages low enough to work in a battery powered beacon device that sends alerts when a temperature threshold is reached.
Second, I am interested in thermal switches as a way to add redundancy in case of failure (sensor malfunctions, power and network outage). For instance, a Sonoff WiFi switch is used to control a fan heater in a greenhouse. One could use a M-TRS5-30B in the output circuit of a Sonoff switch to break the circuit of the heater when temperature exceeds 30C. This is useful in case of Wifi network failure or Sonoff device failure (output always on).
Proposed Work
ARDU-TEMP ALARM prototype
Use a NodeMCU to send alarm messages to IoT monitoring platform (Thingspeak) when temperature exceeds 90C. NodeMCU uses a DC/DC converter in the power supply section. OHD1-90M is used in the power supply section so that when the temp threshold is reached (90+/-5C), the NodeMCU is powered and starts sending alarm messages. I am interested to see how the thermal switch operates at lower voltages (can I use batteries for the beacon device?).
Thanks KEMET and element 14 for selecting me for this design challenge. Looking forward to receiving the kit!