No Exit Zone Sensor Implementation

No Exit / Safe zone detection is another important aspect of the project, as it ensures that the individuals are within the designated area when the balls are launched. This is essential both for safety, ensuring that players are not near the launchers, and for gameplay, ensuring that the players do not cheat by approaching the launcher and reduce the challenge of blocking balls or by standing in a corner that is inaccessible by the launcher. Several options for safe zone detection were evaluated.

Upon the recommendation of Professor Bedi, the group looked into designing a resistive floor using velostat. Velostat is a thin pressure-sensitive material that changes its resistance when pressure is applied. The velostat would be placed under the floor with copper strips above and below the velostat. The copper strips are connected through multiplexors to a microcontroller that would read resistance values at different points to determine the location of the individuals. This would require a number of analog multiplexers and require a significant amount of work to install. Due to this, velostat was deemed too complex and impractical, as it would require a high level of granularity and a fast multiplexer to scan the floor area in real time.

Another option would be to use multiple point LIDARs arrayed like a body light curtain, which is a type of light curtain with greater spacing between the beams than those required to detect hands or fingers. The LIDARs would be placed at the boundary of the safe zone and detect the presence or absence of the individuals. An issue with this implementation is that it only provides confirmation that someone has exited or entered the safe zone. The sensor must also be able to determine if someone is actively outside of the safe zone, this could be achieved through including more point LIDARs arrayed horizontally to cover the rest of the room. However, this has the issue of

requiring several LIDARs which increases the cost and installation complexity.

Using a 2D spinning LIDAR is another possibility. This single LIDAR can scan the entire room and return a 2D point map. The LIDAR would be able to detect the position and shape of the individuals and confirm that they are within the allotted zone. This option was chosen as the most feasible and reliable, as it would provide a complete and accurate view of the safe zone and require only one sensor and a simple setup. Additionally, this technology could be used to aid other Activate rooms such as Hoops and Strike where players must stay behind a throwing line. Also, to further increase the difficulty of the game the LIDAR can track the players position and launch the balls either at the players directly for the dodge game mode, or away from the players for the protect game mode. Another benefit of the spinning LIDAR is that it returns a point cloud which shows players as a collection of points rather than the binary detection of point LIDARs. Also, with the spinning LIDAR the safe zone is implemented in software rather than a physical installation of sensors. This allows for flexibility of changing the safe zone for different game modes or room configurations.

Because of this a 2D LIDAR was deemed to be the best option for determining players location in the room. The RPLIDAR A1 was chosen since it offers ready made Python libraries and a simple USB interface.

Testing with the RPLIDAR revealed that on occasion there would be noise in the signal or points would not clear after a player moved away. Because of this do determine the location of an individual a number of points must be detected within a space to confirm the presence of a player. A visualization of the LIDAR’s field of view along with the safe zone software is shown below. The green box indicates the safe zone and if the number of points in the zone falls below a certain threshold then the program sends an alert detailing that the player has left the safe zone.