Reviewed-on: AllSpice-demos/Demos-home#4

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+  <img src="images/Main_Pwr.jpg" width="600">
+</p>
+
+To see the location of the Jetson Nano (with the large heatsink), we remove the antenna mount and cooling cover just below the fan. The cover assists with airflow through the device and ensures air is pushed across the heat sink.

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+To start with, here is a full-system block diagram, color-coded by approximate function:
+
+<p align="center">
+  <img src="images/BlockDiagramFunction2.jpeg" width="1200">

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+
+One of the most complex systems of the Orb is the power distribution network. Below we describe the main power supplies, EXCLUDING the dedicated ones for the security subsystem which will be covered in its own section.
+
+Since illuminating the eye sufficiently to capture the necessary detail requires a large amount of (pulsed) light and therefore energy, TFH designed their own battery pack to accommodate this requirement.

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+
+Since illuminating the eye sufficiently to capture the necessary detail requires a large amount of (pulsed) light and therefore energy, TFH designed their own battery pack to accommodate this requirement.
+
+The battery is a custom Li-Ion pack consisting of 8x 18650 cells with 3.7V nominal voltage in a 2P4S configuration (14.8V) and a capacity of close to 100Wh. This voltage is transformed into several main rails that power other components:

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+
+(**Note**: It is easier to follow the power tree description by consulting the architecture diagram. We recommend inspecting the diagram in parallel with reading the below descriptions.)
+
+  - **+V_BAT** (**VBAT_SW** in the schematic): This rail is somewhat circular. In normal operation, it is generated directly from +VBAT. However, it can ALSO be supplied from the +12V_CAPS (which is generated from +17V_CAPS, which is charged from +V_BAT)

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+
+  - **+V_BAT** (**VBAT_SW** in the schematic): This rail is somewhat circular. In normal operation, it is generated directly from +VBAT. However, it can ALSO be supplied from the +12V_CAPS (which is generated from +17V_CAPS, which is charged from +V_BAT)
+
+  - **+12V_CAPS**: This rail is created from the +17V_CAPS rail, and is mainly used as a backup to +V_BAT in the case the main battery is removed but shutdown operations are not yet complete. It also supplies the stepper motors, the cooling fan and the liquid lens focusing.

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+
+  - **+17V_CAPS**: These supercapacitors provide the instantaneous current required to run all of the IR illumination LEDs. It is derived from +V_BAT.
+
+  - **PVCC (31V)**: Derived from +17V_CAPS, this is used to actually run the LEDs. Using 31V supercapacitors would be impractical due to size constraints, so the 17V rail is boosted as needed.

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+
+  - **PVCC (31V)**: Derived from +17V_CAPS, this is used to actually run the LEDs. Using 31V supercapacitors would be impractical due to size constraints, so the 17V rail is boosted as needed.
+
+  - **5V**: Directly powers the Nvidia Jetson, stepper motor driver, polarizer motor. Switched down to several further rails:

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+  - **PVCC (31V)**: Derived from +17V_CAPS, this is used to actually run the LEDs. Using 31V supercapacitors would be impractical due to size constraints, so the 17V rail is boosted as needed.
+
+  - **5V**: Directly powers the Nvidia Jetson, stepper motor driver, polarizer motor. Switched down to several further rails:
+    - **3.3V**: These power WiFi, LTE, SSD, NFC, motor drivers, ALS, temperature sensors, IR & thermal cameras and most glue logic (port expanders, comparators etc)

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+
+  - **5V**: Directly powers the Nvidia Jetson, stepper motor driver, polarizer motor. Switched down to several further rails:
+    - **3.3V**: These power WiFi, LTE, SSD, NFC, motor drivers, ALS, temperature sensors, IR & thermal cameras and most glue logic (port expanders, comparators etc)
+    - **1.8V**: TPM module, RGB camera, 2D Time of Flight

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+    - **3.3V**: These power WiFi, LTE, SSD, NFC, motor drivers, ALS, temperature sensors, IR & thermal cameras and most glue logic (port expanders, comparators etc)
+    - **1.8V**: TPM module, RGB camera, 2D Time of Flight
+    - **2.8V**: Thermal camera coprocessor
+    - **3.6V**: 2D Time of Flight

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+    - **1.8V**: TPM module, RGB camera, 2D Time of Flight
+    - **2.8V**: Thermal camera coprocessor
+    - **3.6V**: 2D Time of Flight
+    - **2.8V** LDO: Stable supply for RGB camera

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+
+  - **5V_RGB**: This powers the single RBG LED on the Operator Interface board
+
+  - **3.3V_UC**: Powers the main microcontroller separately for power gating purposes

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+The main goal of the tamper detection is to quickly erase the security keys in the event of an intrusion, even if the main battery and the backup battery are removed. 
+
+This system consists of the following parts:
+  - **4.7V rail**: This rail powers the security subsystem and is derived from +VBAT. This rail also charges the single cell Li-Poly security backup battery. Note that it is NOT derived from VBAT_SW, in order to avoid charging the backup battery from the main supercapacitors in the event of a disconnected main battery.

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+  - **4.7V rail**: This rail powers the security subsystem and is derived from +VBAT. This rail also charges the single cell Li-Poly security backup battery. Note that it is NOT derived from VBAT_SW, in order to avoid charging the backup battery from the main supercapacitors in the event of a disconnected main battery.
+
+
+  - **Small supercapacitor** (missing from block diagram): This acts as a temporary UPS in case even the backup battery gets removed, and provides enough runtime to delete the security keys.

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+
+Since the optical system will be discussed in detail in the next section, we will mention here only the non-imaging components connected to the Jetson.
+
+  - **WiFi**: Orbs include PCEe-based WiFi cards in a M.2 slot. The current Diamond Orb uses a standard AX200 card.

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+
+  - **Main MCU**: This MCU is responsible for controlling most Orb hardware aside from the imaging system. It communicates with the Jetson through a single-wire custom CAN implementation, and is discussed in the next section
+
+  - **MIPI**: This is a standard interface for most image sensors, and is used as such in the Orb for communicating with the main face detection IR-RGB camera and the iris scanning camera.

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+
+  - **I2C**: Another standard interface, this is used by the Jetson to configure the imagers as well as the 2D Time of Flight sensor.
+
+  - **USB**: Several peripherals on the Orb are USB-based. These include the thermal imager, the BLE component of the WiFi card and an internal unused USB port for debugging.

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+One often-asked question when trying to understand a complex hardware system is "How does this even go together?" To help our readers get that question out of the way, this diagram shows the arrangement of the major components by actual PCB or FPC.
+
+<p align="center">
+  <img src="images/ConnectionDiagram.svg" width="800">

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+
+Since the optical system will be discussed in detail in the next section, we will mention here only the non-imaging components connected to the Jetson.
+
+  - **WiFi**: Orbs include PCEe-based WiFi cards in a M.2 slot. The current Diamond Orb uses a standard AX210 card.

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+  - **Sensors**: The Orb contains many internal sensors, which are used for health and status monitoring.
+    - Temperature sensors in various places throughout the device for overtemperature conditions and adjust cooling.
+    - Voltage measurement on every rail to ensure the device’s power supply is operating correctly. Also used for switching between available power sources
+    - Hardware version can be read as an analog voltage (industry standard practise)

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+    - Temperature sensors in various places throughout the device for overtemperature conditions and adjust cooling.
+    - Voltage measurement on every rail to ensure the device’s power supply is operating correctly. Also used for switching between available power sources
+    - Hardware version can be read as an analog voltage (industry standard practise)
+    - IMU: The inertial measurement unit is used to detect Orb motion (drops, displacement, jerks), which can be used to inform tampering or theft decisions.

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+    - Hardware version can be read as an analog voltage (industry standard practise)
+    - IMU: The inertial measurement unit is used to detect Orb motion (drops, displacement, jerks), which can be used to inform tampering or theft decisions.
+
+  - **Cooling**:  The main MCU controls the cooling fan, which mainly cools the Jetson module but also the imaging subassembly via indirect airflow.

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+  - **Liquid Lens**: Part of the optical assembly includes a liquid lens for focusing. This is controlled from the main MCU.
+
+  - **LEDs**: All LEDs on the Orb are driven from the main MCU, though most are located on the Front Unit. Control signals are routed through the Power Board to the Front Unit. There are several sets of LEDs:
+    - **RGBW**: These are individually addressable (clock, data) and are used for indication of state and user positioning.

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+
+  - **Gimbal**: The eye camera sensor has a very narrow field of vision. Therefore, the Orb includes an X-Y scanning gimbal which allows the device to locate the user's eyes in the larger frame recorded by the RGBIR (face) camera. This gimbal is driven by two stepper motors.
+
+  - **Polarizer**: The third stepper motor controls the orientation of the polarizer wheel. This is used for recording IR images in two different light orientations, which helps resolve detail in iris structures.

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+
+The Orb software runs several asynchronous "agents" that execute tasks more or less in parallel. Thus, in order to take images of the users's eye, the following biometric capture tasks run and deliver results to and from each other:
+
+  - Use the RGB/IR "face" camera to track the user's eyes within the frame

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+
+To achieve this, the Orb contains a large number of infrared LEDs in two wavelengths (32x 850nm and 40x 940nm), which flood the user's face during the imaging process described above and allow capturing the necessary amount of detail at the required distance.
+
+We also have a number of RGBW LEDs positioned around the main camera that are used as a user interface of sorts, as well as state indication. The white component of the LEDs is further used to illuminate the entire face during the eye tracking stage of the process.

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+The following image shows the placement of all the LEDs inside the front unit. Please refer to the individual repository for further details.
+
+<p align="center">
+  <img src="images/Illumination.png" width="600">