Week 11 - September 19-25

Note: a header will be included before each topic to provide which module is to be talked about in each section.

Sensor Module

Detection angle for the ultrasonic sensor and range accuracy was tested this week, first by running an example code from an Arduino board to the sensor, and the ranges and angle was estimated to help see when it would detect the presence of an object. The code works as intended and verifies some things while introducing some characteristics of the Ultrasonic sensor. First, it does confirm that it can accurately detect when objects are in front of the sensor, and while the exact distance wasn’t verified, it changed fast enough that a program utilizing the sensor could perform the appropriate action to avoid collision once a certain distance is detected.

For the angle of detection, a small model setup was made to help test if the 15o angle the Sensor’s datasheet is true. Initially it was showing that something was in the way at around 3-4 feet when passing the 15o detection angle in front of the sensor, however the farther an object was from the sensor, the less reliable that zone would get, and an object would need to be more directly in front of the Ultrasonic sensor for detection. This distance, however, can be considered a safe enough distance for this to be negligible, and more instances will be simulated to see what the sensor’s limitations are.

One other thing that was noticed is in some cases, the sensor began to not detect some objects that were standing still even though they were close enough to send a close echo back. This will be monitored to see if it is an issue later when sensors are installed on the cart, but for now since the cart will be moving, an object standing still would still be considered as “moving” so the cart would still be able to see the difference in distance.

Working on the Ultrasonic sensors some more, the angle of detection was tested to see if the 15o angle holds true at varying distances. It seems that on both the ground and on an elevated surface incoming objects from the side do seem to be caught more frequently at longer distances than when close, but if a minimum distance is detected between and object and sensor, the range should be good enough to tell the control module in time there is something and perform the necessary movements to avoid it. Figure 1 is an example of how the testing was done. However, what is less accurate is on the sides of the sensor, where the Ultrasonic sensor failed to pick up objects not directly in front of it but just to the side, which will be problematic due to the size of the cart. If an 18” wide cart was to use solely an ultrasonic sensor to detect motion or objects in front of it, anything within 2 feet may still be collided with, as the ultrasonic sensor would have “blind spots” on the sides of the sensor and would not be able to react in time to adjust its course.

Figure 1: Angle and distance testing on ultrasonic sensor

On the last group meeting held, Victoria suggested on using the IR proximity sensors to double as more of the “corner” sensors instead of just exclusively on the sides of the cart. They would still be used to detect objects on the side in the event obstacle avoidance is necessary, but now they would help compensate for the Ultrasonic sensor’s blind spots on its side when in close proximity of the object. Upon researching the IR sensor’s datasheet, it is found that the sensor is indeed less linear in its detection range and more of an area in front of it, which can be used in our favor to try to cover more of the corners of the rover rather than one side.[] Figures 2 and 3 from the IR receiver module datasheet illustrate this. Figure 4 shows the sensor itself when verifying the proximity sensor operation.

Figure 2 and 3: Proximity sensor directivity ranges

Figure 4: IR proximity sensor, Emitter and receiver side

Some notes about the IR proximity sensors:

From the supplier website, the specs of the sensor to keep in mind are:

Average current drawn at 16mA and 5.5 V max Voltage (keep to 5 V). The sensing range is noted to be maxed out at 24 inches.

It is also worth noting that so far, the IR emitting and receiving from the proximity sensor has no affect on the IR transceiver to be used for direction sensing. Both being on at the same time near each other still produce the expected outputs, and the proximity sensor does not disrupt what the transceiver sees from other IR sources.

Control module

It was found that when no Bluetooth signal is detected and BLE scanner is running (disconnected but tracker code is still calling for RSSI) the function will return a dB value of 127 dB, which indicates no Bluetooth is connected.