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Module's Selected Major Components

Module's Selected Major Components

The following sections are the selected major components necessary for subsystem A3:

Microcontroller Selection

The structure of the EGR314 course this project is being developed in requires the use of either a Microchip PIC-family microcontroller or an Expressif ESP32-S3-WROOM-1-N4 module. As the primary function of this device is bluetooth communication, and the PIC family does not include any units with built-in wireless functionality, the ESP32 will be chosen. Additional benefits of the ESP32 include a more reliable development environment by leveraging open-source tools such as mpremote and Python/MicroPython.

The pinout of the ESP32-S3-WROOM-1-N4 module is as follows:

Subsystem A3's role on the team is to provide a BLE GATT server onboard the robot, and route data between the daisy-chain bus and the BLE communication to the controller unit (systems A1 and A2). To do this, A3 must be capable of recieving unregulated power from the robot's onboard daisy-chain bus and regulate it to it's required 3.3V. No additional sensors, actuators or displays will be used. Simple debug buttons and LEDs will be used to assist with testing.

To perform the necessary bluetooth functions, the aioble library will be used. This library provides a wrapper over MicroPython's bluetooth API, making development simpler and more reliable. This library allows modules for client and server to be loaded individually, reducing the program size.

3.3V Power Regulator

  1. AP63203WU-7 buck switching regulator

    Pros Cons
    Inexpensive Current capacity significantly higher than necessary, could be smaller
    Wide input voltage range
    Low EMI

  2. MP2317GJ-Z buck switching regulator

    Pros Cons
    Adjustable output Expensive
    Small footprint No EMI specs mentioned

  3. TPS62172DSGR buck switching regulator

    Pros Cons
    Very compact Leadless design requires additional assembly equipment
    Low noise
    ### Battery
    No commercially available single cell has sufficient capacity to power the whole drone (estimated 5A peak theoretical draw) for a reasonable time of at least an hour. 12V is our maximum voltage, but the only sufficient cell type that can deliver this is lead-acid, which are heavy and expensive. As such our options are to use a pack of multiple cells. This course's structure does not allow packs with management circuitry built-in, so 12V Li-ion packs with a BMS are not an option. Options will be restricted to disposable packs or externally rechargable packs without an onboard BMS.

A more mature version of this system could integrate it's own charging and battery control circuit using a BQ24616RGER IC. The whole project for this proposed system can be downloaded here. This project was significantly too complex for the remaining time in the course, and should have been proposed as the primary functionality from the beginning.

  1. Amazon Basics 8-pack 9V batteries

    Pros Cons
    Lower price/quantity compared to other options No energy rating provided (assumed to be between 200-500mAh)
    Simple connection Can't power 12V subsystems

  2. Tenergy 12V NIMH rechargable pack

    Pros Cons
    High capacity, can power subsystem for the target duration Less common battery chemistry, harder to find a charger
    Rechargable Expensive with charger
    Can power 12V systems

  3. 12V alkaline pack

    Pros Cons
    High capacity, can power subsystem for the target duration Non-rechargable
    Cheap, can purchase multiple units

The Tenergy 12V NIMH pack and it's charger will be chosen for it's rechargability. While the 12V alkaline pack offers a competitive price to overlook it's disposable nature, crimping new leads to it every time the pack has to be changed will be too time-consuming, and using aligator clips is not a safe option for the current draw the system is capable of. The 9V batteries do not offer a competitive enough price or convenience advantage to outweigh the added complexity of having to supply an additional power source for our 12V systems.