Please note: This is a Citizen Science project for demonstration purposes only
The DF702 uses an ultrasonic radar not dissimilar to a car reverse sensor and is used to measure distances from 15cm to 200cm with an accuracy of 3mm. It also sensors flame risk and inclined (fall) information. The sensor connects to online systems using the LoRaWAN Network and data is sent wirelessly using an ultra-low-power technology on the Australian public class licence radio spectrum on (915Mhz) which is received by LoRaWAN Gateways dotted about Adelaide and the world.
Combined with online systems, data can be measured over time, improving waste management, not just alerting when a bin is full, but also the peak period during days of the week and months of the year and the rate at which it is filled. Improving the effectiveness of waste management for our public spaces and parks.
LoRa Devices use a specially encrypted machine code that can be accessed and decrypted over the internet by registered users of The Things Network. This can then be used by other software applications to store and analyse data, in our case we use an application called NodeRED to process the data into actions, messages and where to store data for later use. The database we are using is InFluxDB which can be used by a website application called Grafana to display data in a more human-friendly graph on a website.
To demonstrate this sensor we choose a public park bin in the City of Port Adelaide Enfield catchment in partnership with our Waste and Recycling Department. The sensor was located on an existing bin in the centre of the park.
In order for the DF702 Sensor to measure the contents of a waste bin, the sensor must be positioned above the bin looking down into the waste area. However, it must also be mounted as not to obstruct the opening allowing the public to put their rubbish into it easily. Also, as the bin contents are accessed through a lid on the top anything attached must allow the lid to be opened and allow the internal bin to be removed and emptied without getting damaged. As this type of sensor also uses radio signals, it cannot be put inside the bin enclosure as the signal would be blocked by the metal casing. However, even if this was not a problem, mounting this type of sensor inside the bin would create an obstruction inhibiting the flow of rubbish.
A bracket was made using a 3mm galvanized steel plate for strength and then coated to reduce rust over time. All sharp edges were removed and attached using tamper-proof stainless security screws to increase the difficulty of removing it without the correct security tool. A rubber mount was also added to reduce vibration and allow some give in cases of accidental collision from passing bikes, trollies or prams.