The FMU receives its power through this connector, coming from the FMU power module. It has two 5V and two ground wires, and one pin for the voltage sensor signal, and another pin for the signal from the current sensor. These sensors are also included in the FMU power module.

We have a separate page about the FMU power module, which provides the power to the power input.

Connector pinout

RDDRONE-FMUK66 Rev. C schematic

RDDRONE-FMUK66 Rev. B schematic

Presently we re-use the standard power adapter from PX4 products. We are working to supply one with the correct JST-GH end already applied.

Power modules include a regulator to adapt from 2S (7.4V), 3S (11.1V), or 4S (14.8V) battery input and provide +/- 5.3V power to the FMU. Some power adapters may allow higher input voltages. In addition to power regulation it includes signals for voltage and current monitoring.

Power distribution

This adapter also passes power through to the rest of the drone or rover platform. In addition there will typically be an additional power distribution board (PDB) to which the drive motors can be connected. A small PDB is included in the HoverGames kit, it should fit in the middle of your drone frame.

ADC 3.3V connector pinout

ADC 6.6V connector pinout

RDDRONE-FMUK66 Rev. C schematic

RDDRONE-FMUK66 Rev. B schematic

Connector pinout

RDDRONE-FMUK66 Rev. C schematic

RDDRONE-FMUK66 Rev. B schematic

DCD stands for Dronecode Debug, and the letters LZ stands for the NXP design partner Landzo and uniquely differentiate it from DCD-M and DCD-S. The DCD-LZ interface used on RDDRONE-FMUK66 is similar to the normal Dronecode debug interface (DCD-M or DCD-S), but with the following changes:

• It is 7 pin instead of 6 pin, the RST line for the MCU is added.

• It uses the same JST-GH connector as the other interfaces instead of the smaller JST-SH or JST-SUR.

Details on the original interfaces can be found here:

Connector pinout

RDDRONE-FMUK66 Rev. C schematic

RDDRONE-FMUK66 Rev. B schematic

Exposed interfaces

ARM SWD debug interface

One of the two interfaces on the DCD-LZ connector is the ARM SWD interface. SWD stands for Serial Wire Debug and is an ARM processor alternative to the JTAG interface. It is what is used to program the board "from scratch" even when there is nothing in the microcontroller memory. This is in contrast to the USB bootloader, which relies on the fact that valid PX4 software is already running.

Note - While the RDRONE-FMUK66 uses NuttX RTOS and the PX4 flight stack by default, any other RTOS and flight stack could be loaded. In fact ANY software compiled for the NXP Kinetis K66 MCU could be loaded including ARM MBED, FreeRTOS, MQX RTOS, or BareMetal code using MCUXpresso and KSDK (Software Development Kit peripheral libraries).

UART / system console

The UART is typically used to access the primary serial console of the target which can be helpful while debugging. Note that this should not be confused with the fact that when PX4 is running a second and third instance of the serial console that are available via the USB interface and telemetry UARTs on board. (Technically the console can be routed to multiple locations). The difference with the primary serial console is that it will show the NuttX bootup sequence of the board and can be used to identify lower level issues before PX4 is even running.

The FMU has a TJA110x two wire automotive ethernet (100BASE-T1) transceiver . However, this is not yet supported by PX4. Adding driver support to PX4 and implementing the protocol might become a HoverGames task/challenge in the future.

Connector pinout

RDDRONE-FMUK66 Rev. C schematic

RDDRONE-FMUK66 Rev. B schematic

In order to work with the DCD-LZ interface you will need a small breakout board which allows you to easily plug in each connector for all devices. The HoverGames kit includes a small board made by NXP which has a 10 pin SWD connector for Segger J-Link debuggers, a USB-TTL-3V3 header. There is also an unused "Landzo" 4 pin serial connector.

Pinout

Schematic

JTAG/SWD 10 pin

The 10 pin connector is small 0.050" pin spacing connector. This is found on the J-Link EDU Mini.

Note that this is officially referred to as a 9 pin connector since the specification calls for a keying plug to be used to block pin 7, over time this seems to have become less common.

USB-TTL-3V3 pinout

Thingiverse case

A small case for this board has been created that can be 3D printed. The case includes an orientation mark for the ground pin of the FTDI cable and a shape which helps correct orientation of the Landzo serial port. The case should be included with the HoverGames kit, and the model is available on .

Cable between FMU and breakout board

The cable is just a 7 pin JST-GH straight through cable.

Connector pinout

RDDRONE-FMUK66 Rev. C schematic

RDDRONE-FMUK66 Rev. B schematic

Dronecode connectors and cable standard

Most interfaces on the RDDRONE-FMUK66 use the JST-GH connectors as specified in the Dronecode Autopilot Connector Standard. The PWM interface uses "standard" RC hobby servo connections. These PWM connectors are 3 pins spaced 0.100" apart.

The male JST-GH connector has a clip on top. As described in the Dronecode standard, the first (leftmost) wire is usually the positive voltage. In some cables this wire is red. The last (rightmost) wire is ground. The wires in between carry different kinds of signals, depending on the function.

RDDRONE-FMUK66 Rev. C connectors

RDDRONE-FMUK66 Rev. C uses the new 10 pin connector for the Holybro GPS module. That GPS module incorporates the arming button and LED, as well as the beeper and an RGB high intensity LED.

Connector pinout

Each connector has its own page with a pinout table and (a part of) the schematic of the connector. Some pages also include additional information relevant to the exposed interfaces. The connector specific pages are listed under this page.

RDDRONE-FMUK66 Rev. B connectors

The pictures below give an overview of all connectors (and LEDs) on the RDDRONE-FMUK66 Rev. B. Most of the labels in the pictures are the same as the labels on the PCB itself.

The FMU has six PWM outputs for controlling motors or servos. Please refer to the assembly guide for the order in which the ESCs should be connected. Make sure to plug in the connectors in the right way. The ground wire (black or brown) should go on top (closest to the board), the signal wire (white or yellow/orange) on the bottom.

The servorail also has a BEC input for powering the 5V rail, which is split from the internal 5V of the FMU and thus not powered when there is no BEC connected. This is done intentionally to isolate this as a source of electrical noise coming into the FMU. Some ESCs or servos require power from the servorail, but the default ESCs included in the HoverGames kit don't need this. They are powered directly from the battery, so it is not required to connect a BEC.

Servo pinout

BEC pinout

RDDRONE-FMUK66 Rev. C schematic

RDDRONE-FMUK66 Rev. B schematic

Connector pinout

RDDRONE-FMUK66 Rev. C schematic

RDDRONE-FMUK66 Rev. B schematic

The serial port can be used to communicate with the FMU either remotely or with a companion computer on the drone itself. Often telemetry radios are connected to this port to provide a wireless connection with a ground control station. By default, PX4 listens and communicates using the MAVLink protocol on this port.

Serial 1 / Telemetry 1 / (UART 4) connector pinout

RDDRONE-FMUK66 Rev. C schematic

RDDRONE-FMUK66 Rev. B schematic

Telemetry

RDDRONE-FMUK66 Rev. C has a single RC input connector. It has PPM/SBUS, RSSI and Spektrum inputs, and a RC output that together with the PPM/SBUS input forms a UART TX/RX pair.

RDDRONE-FMUK66 Rev. B and older revisions had two connectors for input from the radio controller. The FRSKY port supports PPM and SBUS inputs and has telemetry output for an FrSky radio controller. The other connector, labelled RSSI/PPM, supports PPM, SBUS and Spektrum radio protocols. This port also has an RSSI input. FrSky telemetry is impossible when the PPM/SBUS input on either connector is also used.

RDDRONE-FMUK66 Rev. C RC input connector pinout

On older versions of the RDDRONE-FMUK66, this port could only be used as IRDA. Since RDDRONE-FMUK66 Rev. C, it is by default configured as a free UART, which can be used as Telemetry 2 in PX4. It can still be reconfigured to use it as IRDA or as an extra I2C bus, though pull-up resistors will have to be placed by hand.

RDDRONE-FMUK66 Rev. C connector pinout

RDDRONE-FMUK66 Rev. B had a conventional 6 pin GPS connector. On RDDRONE-FMUK66 Rev. C this has been replaced by the 10 pin connector used by the Pixhawk 4 and its GPS. The HoverGames drone kit will also include this GPS. The 10 pin connector also includes the pinout for an arming switch and a buzzer.

Connector pinout

Previous versions of the RDDRONE-FMUK66 included a separate arming switch connector. The HoverGames drone kit would also include a separate arming switch. However, since the release of RDDRONE-FMUK66 Rev. C a is available for the Pixhawk 4 GPS. This GPS module has an arming switch as well.

Since RDDRONE-FMUK66 Rev. C, this connector is not found on the board anymore. The newer FMUs now have a , which has a buzzer inside. There is also no separate buzzer is included in the HoverGames kit anymore.

The RDDRONE-FMUK66 features two . PX4 implements the , and supports some motor controllers, sensors and GPS solutions with a CAN interface. The current HoverGames kit does not include any hardware with a CAN interface, except the FMU itself.

Connector pinout