Smart community use case – Monitoring the freezer in the convenience store
We have a convenience store within our community. It has a freezer which is used to store stuff such as frozen vegetables, ice cream, chicken, meat etc. Freezer temperature has to be below 18 Degree Celsius to prevent growth of harmful bacteria. This can be a problem in India because of frequent power cuts especially during summers. Monitoring freezers and refrigerators can help in detecting spoiled food and thereby avoiding health risks such as food poisoning.
We built a dual temperature monitoring system using a WiSense WSN1101L low power wireless mesh network node operating in the license free band (865 – 867 MHz) in India. This node has two thermistors. One measures the ambient temperature in the store and the other one measures the temperature inside one of the freezers in the store. The temperature data is periodically measured and sent to WiSight (Our cloud storage and visualization app running on Amazon AWS). The node is configured to run as an RFD (reduced functionality device). It is powered by two AAA batteries. Reduced functionality nodes spend most of the time in deep sleep (consuming a couple of micro-amps of current) waking up periodically (say once in 5 minutes) to sense and (if required) report data to the external world via the coordinator node.
The sensor node (located inside the convenience store) is 3 hops away from the coordinator node. The latter is connected to a Raspberry Pi which is forwarding sensor data to WiSight running on AWS.
Here are a few pics of the prototype in action.
You can see the thermistor inside the freezer in the pic below.
A snapshot of temperature data from the freezer over the past couple of days. The freezer has mostly been at around -23 deg C (set point). You can see two spikes followed by a slow return to the set point. Need to analyze the spikes.