My original proposed sensor system is shown in Figure 1. The system consists of a door lock monitor, soldering iron monitors, cat feed monitor, and a plant moisture monitor. The door lock monitor is based on the STM-320U Magnet Contact Transmitter Module, and the soldering iron, cat feed, and plant moisture monitors are based on the STM-332U Temperature Sensor Module.

Each of the monitors and transmits data to a Raspberry Pi Model B+ with a EnOcean Pi Transceiver Module that is captured and processed by the Friend Home automation and Energy Management System (FHEM) server or by the OpenHAB server. These servers are core tools to upgrade my 100+ year old Victorian home into an Internet-of-things Smarthome. My long term goal is to make our home more energy efficient.

Figure 1

The resulting door lock, soldering iron, cat feed and soil moisture monitors are shown in Figure 2. The door lock monitor uses a foam magnet spring and stabilizer assembly, and bolt hole liner that slides into the bolt hole. The STM-320U Magnet Contact Transmitter module is placed in a small housing and attached to the door frame with its reed switch aligned with the magnet assembly. This door lock monitor requires little or no modification to the door or door frame and should work with most not-metal doors and frames.

The soldering iron monitor uses a thermistor assembly that contacts the soldering to indicate if the iron is on using the set point input of the STM-332U Temperature Sensor module. This soldering iron is fairly old and does not offer this feature. The thermistor assembly was add to the soldering stands and no modification to the soldering station was required.

The soil moisture monitor used the HSM-100 humidity sensor, the STM-332U Temperature Sensor Monitor, and a soil resistance probe to measure the moisture content in the soil. The soil resistance probe used the set point input of the STM-332U. The humidity sensor results seem to be inconclusive. It was hard to distinguish the soil moisture level from the background air humidity. My initial packaging may contribute to this as well. The soil resistance provided a good indication if the soil is wet. More data is needed to determine how to use this monitor effectively.

The cat feed monitor used a Force Sensitive Resistor (FSR) to monitor the weight of the cat food in bowl placed on the monitor. The FSR was connected to the set point input of the STM-332U Temperature Sensor Module. A touch sensor and touch pad was also included to detect the presence of a cat feeding using the occupancy switch input of the STM-332U. An unresolved interface issue between the STM-332 and touch sensor prevent me from demonstrating touch feature before the deadline of the design challenge.

Figure 2

Building and testing these monitors occurred over the last 14 days. Most of my time was spent blogging on learning about how the Raspberry Pi, EnOcean Pi, EnOcean senor modules, EnOcean Universal Programmer Board, FHEM server, Tek TBS1052B-EDU Oscilloscope, OpenChoice Desktop, PC Courseware Editor, and Cadsoft Eagle PCB Design Software all works and how to use them in a network for this design challenge. It's been a very educational experience and I’ve learned a lot about building and integrating systems with wireless energy harvesting devices into IoT smart devices. Now, Light is the new battery. I’d like to thank the organizes for selecting me as a finalist and the sponsors for supporting this challenge.