After reviewing the fan control diagram, it became clear that the limited number of GPIO on the MCU would make it very complicated and time-consuming to program and wire the system. Since 32 relays will be used to switch the fans, 32 GPIO pins are required by the fan control module. With some further research, an I2C GPIO expander was found that could increase the GPIO by 16. Since the Raspberry Pi Pico has 26 GPIO pins, the total GPIO will be 42. Neither of the I2C buses on the Pi will be in use otherwise, so this makes a seamless addition to the system. Adafruit makes a breakout board using an MCP23017 chip, and this is what we will use.
The addition of GPIO pins required some modification to the fan control block diagram, so Ian updated it to reflect the changes. Since each GPIO is connected to a relay, the diagram has been greatly simplified.
After these changes were made, Ian wrote sections 2.1 and 2.2 of the proposal report. The updated report is available as a pdf download under 'Proposal Report'.
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