The Sentera Double 4K is a small, fully customizable twin-imager sensor that is universally compatible with any UAV. Fitting in the footprint of a GoPro® HERO 4, the rugged, high-throughput Double 4K Sensor is designed for use in harsh environments with configuration options that make it ideal for use in agriculture and infrastructure inspection applications. Both cameras are capable of capturing high-megapixel color stills, near-infrared (NIR), and normalized difference vegetation index (NDVI) data, and 4K video.


Integration Options


The Sentera Double 4K allows users a large amount of flexibility with how to interface to the camera to provide power as well as power external devices directly from the camera. There are multiple options available for users to interface to with the Sentera Double 4K. These interfaces already support the following hardware devices.

  • Lockheed Martin Kestrel™ autopilot (3.3V UART)
  • Pixhawk™ autopilot (3.3V UART)
  • MAVLink™ based systems (3.3V UART)
  • Sentera™ based systems (100Base-T Ethernet)
  • GPS based triggering/metadata (PWR and 3.3V UART)
  • Sentera Light Sensor (3.3V I2C)
  • Customized ICD options available upon request

Cables to interface to the camera can be purchased directly from Sentera upon request. Major suppliers also offer pre-terminated cables/contacts for users to easily create their own cable installations that suits each users specific requirements.


Hardware Overview


Mechanical CAD Model

A mechanical model of the Double 4k sensor is available for download in STEP file format.


Sentera Double 4K CAD Model (.step)


Electrical Connectors

The following tables list pin descriptions of the camera connectors.  All 3.3V UART and 3.3V I2C interfaces are not 5V tolerant.  For additional detail on camera interfaces please contact Sentera.  J10 is a USB 3.0 connectors and is only used by Sentera during development and testing.


Camera Connectors


J3 - Main Power and Signals

Pin
Signal
Type
Description
1
VCC
PWR
Camera power input (6V to 26V).
2
GND
PWR
3
(3V3) TXD
O
3.3V UART bus.
4
(3V3) RXD
I
5
VCC_3V3
PWR
3.3V switched power output - selectable upon request.
6
(3V3)SDA
I/O
3.3V I2C bus.
7
(3V3)SCL
I/O
8
EN_A
PWR
3.3V switched power output (with pin 5) - selectable upon request.
9
GPIO_B2
I/O
Reserved.
10
RSVD
N/A
Reserved.
Connector: BM10B-GHS-TBT
Mating Connector: GHR-10V-S


J4 - Ethernet Pin Descriptions

Pin
Signal
Description
1
TD0P
Transmit Data+ or BiDirectional.
2
TD0N
Transmit Data- or BiDirectional.
3
TD1P
Receive Data+ or BiDirectional.
4
TD1N
Receive Data- or BiDirectional.
5
TD2P
Not connected or BiDirectional.
6
TD2N
Not connected or BiDirectional.
7
TD3P
Not connected or BiDirectional.
8
TD3N
Not connected or BiDirectional.
Connector: BM10B-GHS-TBT
Mating Connector: GHR-08V-S


J5 - Auxiliary Power and Signals

Pin
Signal
Type
Description
1
GND
PWR
3.3V power output.
2
VCC_3V3
PWR
3
EN_B
PWR
5.0V switched power output - selectable upon request.
4
VCC_5V0
PWR
5
(3V3)SCL
I/O
3.3V I2C bus.
6
(3V3)SDA
I/O
7
(3V3)RX1
I
3.3V UART bus.
8
(3V3)TX1
O
9
(3V3) RXD
I
3.3V UART bus.
10
(3V3) TXD
O
11
GND
PWR
Camera power input (6V to 26V).
12
VCC
PWR
Connector: BM12B-GHS-TBT
Mating Connector: GHR-12V-S


The camera is able to auto-negotiate the Enternet speed.  Therefore, only four pins are required for a slower 10Base-T or 100Base-T speeds.  All eight pins are required for communication at a 1000Base-T speed.


Typical users will choose either J3 OR J5 depending on their specific installation requirements. Many of the signals are shared between J3 and J5 including the primary input power, UART, and I2C connections.  The following connections are shared between the connectors:

  • Camera power input (6V to 26V): VCC & GND
  • J3: pins 1-2
  • J5: pins 11-12
    • 3.3V UART bus: RXD & TXD
  • J3: pins 3-4
  • J5: pins 9-10
    • 3.3V I2C bus: SCL & SDA
  • J3: pins 6-7
  • J5: pins 5-6

Display Indicators

The camera contains two indicators for providing feedback on the camera’s operation. The indicator closest to the top of the camera identifies camera “Power”, while the indicator closest to the bottom of the camera identifies camera “Status”.  Each display indicator contains a set of LEDs; a green LED and a red LED.



Once the camera is powered, both the green and red LED of the Power indicator will be on.  The status indicator LED uses both a green and red LED to indicate the current state of the system, per the following diagram.



Initialization
OperationThe camera is initializing its components and performing startup functions.

State TimeCamera initialization can take up to 60 seconds.

Transition: The camera transitions to the idle state immediately after initialization of all camera components are completed.

Status IndicatorOff or flashing red.
Idle
Operation: The camera is waiting to start a session.  Criteria for starting a session are based on configuration setting – see section Operation Modes.

State Time: The state occurs indefinitely until criteria are met for starting the session.

TransitionThe camera transitions to the active state once a session is started.  Transition from the idle to active state can take up to 20 seconds.

Status IndicatorSolid green.
Active
Operation: The camera is able to take pictures and log these pictures along with metadata to the SD card. This state cannot be entered if the SDcard is missing or corrupt.

State TimeThis state occurs indefinitely until criteria is met for closing the session.

Transition: Transition to the idle state occurs if the session is closed.

Status IndicatorFlashing green.

Operation Modes


Several operation modes are possible with the camera.  Operation modes are categorized by the protocol which is used to communicate with the camera.


For details on more modes, see the Double 4k config.yml Appendix


Sentera Camera Control Protocol


The Sentera Camera Control Protocol (SCCP) is a specification developed by Sentera to provide full control of camera functionality.  The electrical interface the camera uses for communicating SCCP data is the Ethernet interface (connector J4).  Contact Sentera for a definition of this specification.



Session Type

With SCCP mode, a single session type is supported.  The session type is selected in file “config.yml” with the attribute “SessionType”.


SessionType Value
Description
COMMAND
Starting and closing of a camera session is a specific message within the SCCP specification.  This message allows for starting a session with a given name and timestamp.


Trigger Type

With SCCP mode, multiple trigger types are supported.  These trigger types define the criteria necessary for triggering the camera to take pictures.  The trigger type is selected in file “config.yml” with the attribute “Triggertype”.


TriggerType Value
Description
(Recommended)
COMMAND
Triggering of a picture is controlled by a specific message within the SCCP specification.  This message allows for real-time selection of multiple trigger modes (e.g. single picture, GPS distance, GPS overlap, etc.)
INTERVAL
Pictures will be taken at a periodic interval after the session is started.  The interval time is specified by configuration attribute “IntervalSeconds”.


 


MAVLink Protocol

In this mode, the MAVLink protocol is used to supply the camera aircraft data and to trigger the camera to take pictures.  The electrical interface the camera uses for ingesting MAVLink data is the 3.3V UART RXD/TXD pins.  The tables below identify the MAVLink messages (and fields), which are required for camera operation.  See the MAVLink protocol specification for additional detail on message content.


SYSTEM_TIME ( #2 )
Message Field
Description
time_unix_usec
Time since epoch.


ATTITUDE ( #30 )
Message Field
Description
roll
Roll angle.
pitch
Pitch angle.
yaw
Yaw angle.


GLOBAL_POSITION_INT ( #33 )
Message Field
Description
lat
Latitude.
lon
Longitude.
alt
Altitude – AMSL.
relative_alt
Altitude – AGL.


COMMAND_LONG ( #76 )
Message Field
Description
command
Command ID.


Session Type

With the MAVLink protocol mode, multiple session types are supported.  These session types define the criteria necessary for starting a camera session.  The session type is selected in file “config.yml” with the attribute “SessionType”.


SessionType Value
Description
(Recommended)
GPS_FIX
The camera will start a session once GPS data is valid.  The validity of GPS data is identified when an SYSTEM_TIME message is received which is valid (i.e. "time_unix_usec" not equal to zero) and a GLOBAL_POSITION_INT message is received which is valid (i.e. "lat" & "lon" not equal to zero).
IMMEDIATE
The camera will start a session immediately once camera initialization is complete.  This operation has the disadvantage that image metadata is not guaranteed to be valid.


Trigger Type

With the MAVLink protocol mode, multiple trigger types are supported.  These trigger types define the criteria necessary for triggering the camera to take pictures.  The trigger type is selected in file “config.yml” with the attribute “Triggertype”.


TriggerType Value
Description
(Recommended)
COMMAND
The COMMAND_LONG message triggers the camera.  Specifically, the "command" field of this message must be set as MAV_CMD_DO_DIGICAM_CONTROL (value: 203) to trigger the camera.
INTERVAL
Pictures will be taken at a periodic interval after the session is started.  The interval time is specified by configuration attribute “IntervalSeconds”.



U-BLOX Protocol [Including Inspire/Phantom Systems]

In this mode u-blox GPS data is used to determine when to start a session and when to take pictures.  The electrical interface the camera uses for ingesting u-blox data is the 3.3V UART RXD/TXD pins. Necessary u-blox messages are:


Message
Description
UBX-NAV-POSLLH
Geodetic Position Solution.
UBX-NAV-SOL
Navigation Solution Information
UBX-NAV-TIMEUTC
UTC Time Solution.


Session Type

With the u-blox protocol mode, multiple session types are supported.  These session types define the criteria necessary for starting a camera session.  The session type is selected in file “config.yml” with an attribute “SessionType”.


SessionType Value
Description
(Recommended)
GPS_FIX
The camera will start a session once GPS fix has been achieved.  A GPS fix is identified once the GPS positional accuracy (“pAcc” of message UBX-NAV-SOL) is less than configuration attribute “AccurateFixMeters”.
IMMEDIATE
The camera will start a session immediately once camera initialization is complete.  This operation has the disadvantage that image metadata is not guaranteed to be valid.


Trigger Type

With the u-blox protocol mode, multiple trigger types are supported.  These trigger types define the criteria necessary for triggering the camera to take pictures.  The trigger type is selected in file “config.yml” with an attribute “Triggertype”.


TriggerType Value
Description
DISTANCE
A picture is taken when the camera moves a fixed 3-dimensional distance.  The distance is specified by configuration attribute “TriggerDistanceMeters”.
KNOWN_HEIGHT_OVERLAP
The camera takes pictures to achieve an overlap percentage with a fixed UAV height.  The overlap percentage (“KnownHeightOverlapConfig >> OverlapPercent”) and fixed UAV height (“KnownHeightAGLMeters”) are both configuration attributes.
AUTO_HEIGHT_OVERLAP
The camera takes pictures to achieve an overlap percentage with a variable UAV height.  In this mode, the UAV’s height above ground is calculated as the current altitude minus the takeoff altitude.  The overlap percentage (“AutoHeightOverlapConfig  >> OverlapPercent”) is a configuration attribute.
INTERVAL
Pictures will be taken at a periodic interval after the session is started.  The interval time is specified by configuration attribute “IntervalSeconds”.