This week significant progress was made on the sensor module compared to other weeks. First off, I decided to formalize the testing I described in previous reports integrating the NodeMcu with the IR sensor. For this testing, I set up my circuitry as depicted below:
The IR Sensor was powered by a lab power supply set at 4.8V and the NodeMcu was powered directly from my computer via MicroUSB. As you can see I decided to attach a voltmeter in between the output voltage of the sensor coming into the analog A0 port of the NodeMcu and ground in order to measure the voltage going into the NodeMcu. Following my research into the Arduino IDE and the NodeMcu capabilities, I discovered that the analog voltage coming in can be read by the native analogRead() function that has a 10-bit resolution measurement capability courtesy of its analog to digital converter. Rather than outputting the voltage measured directly like a voltmeter would, the function outputs an integer reading that is mapped and correlated to the voltage and ranges from 0-1023. With this in mind I developed the following simple script in order to determine the correlation between the voltage measured by the voltmeter and the digital reading outputted by the analogRead() function:
With the script set and uploaded to the NodeMcu, I placed the sensor near the edge of the table and used a measuring tape (in inches) in order to observe how the voltage and the digital reading changed based on the distance I stood from the sensor.
With this setup in place I utilized the serial monitor and the serial plotter from the Arduino IDE in order to sample and record the digital output of the sricpt, and note by hand the voltage I saw on the voltmeter in front of me. I compiled the data and produced the following table and graphs:
I recorded Low and High voltages and ADC readings respectively since the measurement was not exactly smooth. Therefore, I noted the highest and lowest voltages measured by the meter and the peaks and valleys in the serial plotter corresponding to the ADC reading. In addition to relating the distance with the output voltage and the ADC readings, I related the ADC readings with the voltage and produced the following plots from our data table:
As expected, the measurements were more accurate than the ones obtained in the informal purely analog testing described a few weeks back using the LED setup. The shape of the curves also met our expectations and resembles the one provided by the sensor manufacturer. Having said that, our plots are not exact reflections of the manufacturer graph, but close enough for the purposes of our implementation. I do recognize that there are some errors that come from the experimental setup and human measurements. Thus, the plot discrepancy could be attributed to our testing methodology. Nonetheless, the testing was conducted methodically and as carefully as possible. Thus I was confident that this data would serve as the basis for our algorithm development.
With this data in mind , I was able to create an Arduino Script for the NodeMcu that used the ADC readings to calculate the distance from the IR sensor in inches. This script was developed with the intention of using the calculated distance as the metric that would determine whether or not occupancy data would be sent by the NodeMcu. However, after some testing, I realized my algorithm and my script were not as precise near boundary distances of detection like 3.5ft as established by our design requirements. In other words, this was not sufficient to meet our detection accuracy since it was imprecise in situations where we needed it to be precise.
As a result, I looked at the data once again and utilized the relatively linear relationship between ADC and voltage in order to produce a simpler yet more accurate script. I also modified the circuitry and added an LED connected in between the D4 port and GND that would reflect the behavior of the sensor. The red LED would turn on when the distance was above 3.5ft and off when the distance was less than that. The blue LED embedded in the NodeMcu would do the opposite.
This algorithm produced better results near the 3.5ft boundary. I also tried to test different detection angles and the sensor did not detect at big angles from the center line if none at all. The sensor pretty much worked in a straight line, which is good news for us.
With this phase of testing complete, I shifted my focus to making the sensor module mobile by incorporating the batteries from our design report. At first, I hooked everything up to the power supply but then proceed to use batteries instead. Regardless, the circuit configuration was the following:
I was able to get everything working both with the DC power supply and the battery pack, effectively creating a fully functioning and mobile sensor module, albeit without Wi-Fi capabilities just yet.
In addition, I measured the output voltage produced by the pack which turned out to be 5.4V (fully charged pack) (higher than the expected 4.8V). In addition, each cell is rated with 2,800mAh which brings the grand total to 11,200mAh. With this in mind, I decided to measure the current drawn by the sensor and NodeMcu individually, while detecting something in the desired range and while not. The NodeMcu registered a peak of 59mA while detecting and a low of 25mA while not detecting. On the other hand, the IR sensor readings from the multimeter unstably fluctuated to the point that no set measurement could be made. Nonetheless it did not surpass the 30mA mark that we had expected based on our research for the design report. Further power consumption studies need to be made with a fully Wi-Fi transmitting module, yet, based on our worse predictions of peak consumption, we estimate that we will meet the battery life requirement of 16.5 hours and perhaps surpass it. I was also employing a battery pack with a switch that could greatly extend our battery life. However, further testing will determine which pack is necessary and will be chosen for the module (static or switch enabled pack).
Aside from this, I started preliminary work on the fabrication of the senor encasing using Solidworks. Yet a possible implementation using AutoCAD, laser cutters, and acrylic plastic could be a solution as well.
In consequence, for next week my plan is to integrate the sensor and NodeMcu to transmit occupancy data with my teammates and then proceed to study the power consumption. Afterwards, I will shift my focus to the encasing and the mounting mechanism. I must acknowledge it is a tight schedule due to my limited knowledge of AutoCAD and Solidworks, yet I and the team in general is on pace according to the revised Gantt chart and schedule posted on 4/3.
