2.2.2 Summary of Tests Conducted Step Down Circuit. We have completed these four tests successfully.

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1 2.2.2 Summary of Tests Conducted We have completed these four tests successfully. 1. First, we were able to successfully set up a Raspberry Pi 3 as a server and have other devices go on to the blank html page through IP address. 2. Next, obtaining data from a sensor from a separate Raspberry Pi 3, we were able to send the data up to the server and store it in a blank.csv file we created beforehand. This process was obtained by using PHP and Python coding. 3. From the saved.csv file, we were able to open the file and extract the data to be able to display it onto a chart on the website. 4. Finally, we were able to obtain data from a handheld AeroQual Sensor using an analog to digital converter. Displaying the data in terminal on the RPi allowed us to calculate it to be in a 90% accuracy Figure 5: Temperature and Humidity. Ozone Test Step Down Circuit In order for the system to transmit data in remote locations, we need to make the system fully self-sufficient. We have a 12 V battery that is connected to a voltage regulator and 20-Watt Solar Panel s. We need to step down the voltage from 12 V (Battery), to 9V (Particulate Sensor) and to 5V (Raspberry Pi). We designed and printed a PCB Board, using Autodesk Eagle. Below are the schematics, and the finished PCB Board Design that was sent to Osh Park. Figure 6: is showing the final schematic that was printed by OSH Park. The schematic uses two LM317 as the voltage regulator, each are controlled by two resistors and capacitors of different values to output two voltages one at 5V and the other at 9V. Resistor & Capacitor Values R1: 1500 R2: 240 R3:1500 R4:720 C1 & C3:.1uF Figure 6: The PCB schematic C2 & C4: 1uF 17

2 When we tested the finished, and soldered product, it produced its threshold graph. We connected the voltage regulator to a DC Power Supply and stepped it down 1 Volt at a time, starting at 12 Volts. The voltage regulator maintains it wanted output of 5.11 V till the input voltage drops below 7V, and its wanted voltage of 9.6 volts is drops linearly when the input voltage is below 11 V shown in table 2, and graph 1. In the circuit, we originally wanted the voltage regulator to power the RPI, but since the RPI doesn t have a sleep mode, and runs continuously, it draws 5 watts consistently. In order to combat this issue, we then used the 5V output from the voltage regulator to power the PIC18F20 and relays to controls when the system turns on and off. The voltage regulator isn t used for its intended purpose, which was to power the RPI. Figure 7: The schematic of the Voltage Regulator Voltage (V) 5 Volts (V) 9 Volts (V) Table 2: Voltage Regulator at different Voltages Graph 1: Graph of Voltage Regulator Threshold 18

3 2.2.2 Power Chart of Components The charts below are showing the different sensors that are connected to the system. The columns are representing the input voltage, current, watt/hours and then energy used over a 24- hour period of time. SENSOR POWER CHART Input Voltage (V) Current (Amps) Watt (W) 24 Hour Period (Wh per day) RPI MODEL 3 B 5.1 V.8 A 4 W 96 Wh W/ CO2 & T/H CO2 5 V.2 A 1 W RPI Wh PARTICLE 9 V.003 A.027 W 6.48 Wh SENSOR OZONE 12 V.5 A 6 W 144 Wh TEMPERATURE/ HUMIDITY SERVO (2) COMBINED VOLTAGE REGULATOR 3.5 V.0003 A 1 mw RPI Wh 4.8 V each.0089 A.0178 A.427 W.854 W 10.2 Wh 24.5 Wh 12 V.08 A.96 W W h Total: 1.4 A W Wh RPI (AMPS) GPIO WIFI HDMI LED S KEYBOARDS RPI CONSERVATION Boot:.75 amps, Idle:.35 amps 50 ma across all Pins Individual GPIO Pin draws 16mA ~ 40 ma 50 ma 5 ma Per 100 ma ma dependent on type 19

4 2.2.3 Simulated MATLAB Solar Panel Tests To better understand the system and the power that all the devices consume, we need to know how much power our solar panels will produce in order to see if this system will be selfsufficient. The below to the right show the IV curve, and the Power Curves that were generated with MATLAB, and MATLAB Simulink [6]. Within the simulation, they are the most ideal conditions for a solar panel, the standard test conditions (STC) which temperature reference is approximately 25 C for the working solar panel, 1000 irradiance (W/m 2 ) in order to produce the results on the back of the panel. Within the block diagrams in Simulink, the charge of an electron (1.6e -19 C), Boltzmann s constant (1.38e -23 ), with the atmospheric density (AM) at 1.5, and the energy bandgap of a cell are used (1.12eV) are used alongside the different irradiances the solar panel (1000 W/m 2 ), and the open circuit voltage (22.5 V), and short circuit current (5.75 A). The max output voltage that was produced in MATLAB Simulink is Volts, while the max power of the solar panels is at Watts. Graph 2: Simulated IV Curve Graph 3: Simulated Power Curve 20

5 2.2.4 Solar Panel Tests The solar panels test was conducted perpendicular to the sun. A 100 ohm, and a 50 ohm rheostat was used in the circuit portrayed in the image below to change the resistance within the circuit in order to generate a IV curve of the 100 Watt Solar Panels. The IV curve will specifically will tell us the performance of the solar panels. The temperature during the test was approximately 76 degrees, and there was little haze in the sky. It took approximately 30 minutes to obtain all the voltages and record Figure 8: Solar Panel Test Schematic the resistances of the rheostats and the voltages. Over the duration of obtaining data, the sun angle had shifted, and the haze in the sky had become greater. As a solar panel heats up, they lose their efficiency. Under the most ideal conditions, the performance of the solar panel will produce what the statistics are located on the backside of the panel, which for our case is 100 Watts. Solar panels are most efficient when they are in cold temperatures and perpendicular to the sun. In our case, the panel had been in the sun for about an hour before performing the test. Therefore, when we tested for an open circuit, the solar panel (Voc) should produce about 22.5 Volts, but in our case, the open circuit voltage read 22.5 and the voltage dropped about.01 volts every 5 seconds due to the heating up of the solar panel. Below is the graph that was produced in said conditions. The max voltage is V, and the max power that is produced within this test is approximately watts. Resistance (Ω) Voltage (V) Current (I) Power (W) Open Circuit Short Table 3: Solar Panel IV Curve 21

6 Generated from the table above is the IV Curve, and the power curve of the 100 Watt Solar Panels. The simulated results from Matlab Simulink gave us a reading of Volts, and the measured reading was volts, which is a difference of.71 volts between simulation and tested. The max power that was tested was approximately watts, and the simulated max power was watts, giving a difference of 63 watts. 3 IV CURVE CHARACTERISTICS VOLTAGE (VOLTS) CURRENT (AMPS) Graph 4: Tested IV Curve The chart below is depicting the max power at 35 watts which is lower than the ratings on the back of the panel and from the simulated tests. The simulated test was the most ideal conditions and the rating on the solar panel is the standard test conditions (STC). On the next page, it shows the differences between the simulated and tested POWER CHARACTERISTICS POEWR (WATTS) VOLTAGE (VOLTS) Graph 5: Tested Power Curve

7 The chart below is showing the simulated versus tested results, the simulated results use MATALB Simulink under ideal conditions, while the tested is how we tested in the environment and the different factors that contributed to our data. Table 4: Simulated VS Tested IV Curve 23

8 2.2.5 Photometer Tests In our project there are a lot of obstacles to overcome. One of them is to deal with one of the several sensors that we obtained which is the Global Photometer. The downside of this device is that it requires itself to be pointed at the sun for it to obtain accurate data readings. Brainstorming for several ideas that wouldn t add vast amounts of complexity. An idea that we ve come up with is to use the already existing ten channel analog to digital converter and use it for taking data in from photoresistors placed at each corner of the face of the sensor. Each value would then be added to its corresponding position in terms of left and right as well as up and down. These are then calculated and placed through comparators which move the position of the servos to align the sensor to the point of highest intensity. The sensitivity and threshold values can easily be changed in the software. Upon execution, it was present that the main controller of our project, the Raspberry Pi 3 model B did not easily support high quality drivers for the servos or PWM signals. The movement is limited to increments of approximately 15 degrees in any direction. Another problem that may be faced is the duration of the signal that is sent to the servos. It is noted that servos move from a command that they are given in terms of a signal. The length of the duty cycle refers to the position. In most cases the signal is between 1 and 2 ms. 1 denoting the position of 0 and 2 at 180 as noted in figure B. Therefore, the servo holds the position as long as the signal is present and enters limp once the PWM signal is stopped. In our case we did not want to have it running constantly due to the imperfect PWM present in the Raspberry Pi which will lead to the inevitable jerking. Figure 9: Servo Signals 24