The main objective for these two weeks was to complete the main program and get the control module soldered to a PCB prototype board. The main program integration was simple. The codes for each sensor were separated into different files, so the first step was to combine them. Once that was complete, fan control functions were written to act on temperature differentials and battery level. This is shown in the code below.
To plan the connections, the Raspberry Pi Pico and sensor components were laid out on PCB and their positions were recorded on a spreadsheet. The same was done for the GPIO expander, which had to be placed on a separate PCB due to space limitations. These sheets were mirrored and then printed out to draw out the connections with a sharpie before soldering.
Figure 1 - Pico PCB layout includes the majority of sensor components.
Figure 2 - The PCF8575 PCB includes parallel resistors with equivalent resistance of 73.3 Ω to drive a green LED.
Figure 3 - Front and back of the soldered Pico PCB.
Figure 4 - Front and back of the soldered PCF8575 PCB.
Next, the IR LEDs and IR Photodiodes were soldered onto PCB cutlets along with wiring. These are shown below.
Figure 5 - Proximity sensor heads soldered to PCB cutlets.
Next, the wiring was planned out for the sensors and fans. The sketch below gives a rough diagram of sensor wiring. To make wiring simple, each window will have one cable for sensors. The cable will carry 5 lines:
IR LED Anode
IR Photodiode Cathode
IR LED Cathode
Thermistor Positive Lead
Ground
Figure 5 - Sensor Wiring diagram
The connection for the green LED Anode will be run on its own line zip tied to the sensor cable for Window 1. In the control module box, the green LED, Window 1 and Window 2 sensor lines will split out into an 11 pin male terminal block, which will plug into a female PCB soldered terminal block. Likewise, the Window 3, Window 4, and battery connections will be split into a 12 pin terminal block combination.
Figure 6 - Terminal block combination.
Similarly, the fan connections will run along two 4-pin connectors per window. 14-pin terminal blocks will provide connection for each pair of windows to the transistor array.
Figure 7 - Fan wiring diagram
Once all the connectors were ordered, Ian updated the website's Diagrams and Flowcharts page and the Engineering Specifications to reflect the recent design changes. An "Added Materials" section was added to the project Budget page to show cost of components ordered after the winter break. A progress report was submitted to IEEE region 3 summarizing the progress made since the end of November, 2022.
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