Solutions for presence detection in an intercom door station

Abstract

In this work, different solutions for human presence detection in a door intercom device are examined.
The study was conducted at a company in Lund, Sweden. The aspiration was to have a reliable presence detection to be able to put the device in sleep mode when not used, and the current solution is not optimal because of limiting design requirements and false triggers. In the project, several different sensor technologies and sensors were examined and evaluated. After an initial selection, four different
sensor technologies were studied and six different sensors using these technologies were investigated and examined both theoretically and practically during tests. The sensor technologies explored were passive IR, active IR, ultrasonic and radar. With the knowledge gained during the investigation and experiments, the different sensors suitability for the project were discussed and evaluated.
The technology most appropriate for this project was found to be radar, due to its ability to easily be installed and integrated inside the intercom since it can function through a lot of materials, including the hardened glass found on the device. While the first radar sensor that was tested demonstrated the potential of the technology, it was found to be a bit too simple. There are a lot of sophisticated radar sensors available but after much investigation the one ultimately chosen was the 60 GHz Acconeer A121 Pulsed Coherent Radar Sensor due to its compatibility with the specific use case. This sensor allows for a much smarter presence detection than the one currently used in the intercom. After testing and
learning about the sensor it was concluded that it could be integrated into the intercom’s PCB and function through the hardened glass panel on the front. This makes it much easier to implement than the currently used solution by having less limiting requirements on the mechanical design of the intercom.
The sensor enables more efficient presence detection because of the ability to activate only when someone approaches, and filtering out unwanted triggers with the help of the sensor’s high accuracy.

Popular Abstract

With global warming being an ever-looming threat,
there is a need to decrease our carbon footprints.
This can be done in several ways – from large
changes like electrifying our current modes of transportation, to smaller things such as turning off devices when no one is using them. This project has
examined different presence detection technologies
to implement in a door station. In the same way
that the lights in a public restroom only turn on for
a limited time after someone enters, a door station
can be built in a way that allows it to turn off when
no one is close to it. This allows for lower energy
consumption which not only saves on electricity but
also increases the life span of the components.
The product this was tested on was an intercom
door station, but the findings from this project
would be applicable to other devices that face similar environments. To place electric equipment outside there is a need for weatherproofing. This gives
rise to limitations when designing the parts of the
door station that interacts with the outside world.
Currently, a PIR (passive infrared) sensor is used
to detect if there is any movement in front of the
sensor. This is done by measuring if there is any
temperature change in front of the sensor. A problem with PIR sensors is that they work much better
at spotting if someone walks past the sensor than if
someone walks towards it, this makes them prone
to false triggers. Another problem is that IR light
can’t penetrate most materials, this puts some very
limiting requirements on the mechanical design of
the product as a special plastic cover needs to be
placed in front of the sensor to weatherproof it.
This plastic cover is both difficult to source and
difficult to get certified as a sealing material. The
goal of the project was to find a different technology that solved these problems. To accomplish this
goal, several different technologies and sensors were
researched, tested, and evaluated. A type of radar
sensor called "Pulsed Coherent Radar" that uses
a frequency of 60 GHz was chosen. This sensor
is very small and energy efficient. It can also be
placed behind the intercom’s hardened glass panel
on the front with minimal impact on the ability to
see and track people.
The reason radar sensors are a great solution for
presence detection in this product is because of how
easy it is to implement and the mechanical design
freedom of the product it provides. There are also
additional benefits, for example, because of the accuracy of the sensor, smart algorithms can be created that only wake the device up when a person
is approaching the product. It can differentiate between someone walking away or someone walking
past the product and filter those out. This makes
the presence detection even more efficient. There
is also a possibility of having gesture control with
the sensor thanks to the high accuracy it provides.

• author: Bengtsson, Anton and Andreasson, Måns
• supervisor: Johan Björnstedt; Francisco Marquez
• organization: Industrial Electrical Engineering and Automation
• course: EIEM01 20231
• year: 2023
• type: H3 - Professional qualifications (4 Years - )
• subject: Technology and Engineering
• keywords: presence detection, sensor technology, PIR, ultrasonic, radar, intercom
• publication/series: CODEN:LUTEDX/TEIE
• report number: 5500
• language: English
• id: 9129725
• date added to LUP: 2023-08-29 13:18:56
• date last changed: 2023-08-29 16:27:20