Pixhawk4-Mini Flight Controller

The Pixhawk4-Mini flight controller is sold by Holybro

Features

  • STM32F765 microcontroller
  • Two IMUs: ICM20689 and BMI055
  • MS5611 SPI barometer
  • builtin I2C IST8310 magnetometer
  • microSD card slot
  • 5 UARTs plus USB
  • 11 PWM outputs
  • Two I2C and one CAN ports
  • External Buzzer
  • External safety Switch
  • Dedicated power input port for external power modules

Pinout

../_images/PH4-mini-pinout.jpg

UART Mapping

  • SERIAL0 -> USB
  • SERIAL1 -> USART2 (Telem1)
  • SERIAL2 -> UART4 (Telem2)
  • SERIAL3 -> UART1 (GPS)
  • SERIAL4 -> UART6 (RCIN port)
  • SERIAL5 -> UART7 (debug)

The SERIAL1 port has RTS/CTS pins, the other UARTs do not have RTS/CTS.

The RCIN port can be used as RX or TX as a general UART using the SERIAL4_OPTIONS bits to swap pins. It is not used for RC input (the PPM pin is used for RC input)

The UART7 connector is inside the case and labelled as debug, but is available as a general purpose UART with ArduPilot.

RC Input

The PPM pin, which by default is mapped to a timer input, can be used for all ArduPilot supported receiver protocols, except CRSF which requires a true UART connection. However, bi-directional protocols which include telemetry, such as SRXL2 and FPort, when connected in this manner, will only provide RC without telemetry.

To allow CRSF and embedded telemetry available in Fport, CRSF, and SRXL2 receivers, the RCIN port’s RCIN pin can also be configured to be used as true UART RX or TX pin for use with bi-directional systems by setting the SERIAL4 parameters appropriately.

To use RCIN for bi-directional RC and Telemetry protocols, SERIAL4_PROTOCOL must be set to “23”, and:

  • PPM is not supported.
  • SBUS/DSM/SRXL connects to the RCIN pin, but SBUS requires that the SERIAL4_OPTIONS be set to “3” to invert the signal.
  • FPort requires connection to RCIN and SERIAL4_OPTIONS be set to “15”.
  • CRSF requires connection to both RX and TX of a UART, so the RCIN port and pin cannot be used. Instead either SERIAL1 (UART2), SERIAL2 (UART4), or SERIAL3 (UART1 must be used. Set its protocol to “23” and options to “0”.
  • SRXL2 requires a connection to RCIN and automatically provides telemetry. Set SERIAL4_OPTIONS to “4”.

Any UART can be used for RC system connections in ArduPilot also, and is compatible with all protocols except PPM. See Radio Control Systems for details.

PWM Output

The Pixhawk4-Mini supports up to 11 PWM outputs. All 11 outputs support all normal PWM output formats. All outputs except numbers 7 and 8 support DShot.

The first 8 outputs are labelled “MAIN OUT” on the case. The next 3 outputs are labelled CAP1 to CAP3 on the case. The CAP4 pin cannot be used as a PWM output.

In order to use outputs 9, 10 and 11 you need to change BRD_PWM_COUNT to 11.

The 11 PWM outputs are in 4 groups:

  • PWM 1, 2, 3 and 4 in group1
  • PWM 5 and 6 in group2
  • PWM 7 and 8 in group3
  • PWM 9, 10 and 11 in group4

Channels within the same group need to use the same output rate. If any channel in a group uses DShot then all channels in the group need to use DShot.

Battery Monitoring

The board has a dedicated power monitor port with a 6 pin connector. The correct battery setting parameters are dependent on the type of power module which is connected.

Compass

The Pixhawk4-Mini has a builtin IST8310 compass. Due to potential interference the board is usually used with an external I2C compass as part of a GPS/Compass combination.

GPIOs

The 11 PWM ports plus the CAP4 ports can be used as GPIOs (relays, buttons, RPM etc). To use them you need to limit the number of these pins that is used for PWM by setting the BRD_PWM_COUNT to a number less than 11. See GPIOs page for more information.

For example if you set BRD_PWM_COUNT to 8 then CAP1, CAP2 and CAP3 will be available for use as GPIOs, in addition to CAP4.

The numbering of the GPIOs for PIN variables in ArduPilot is:

  • PWM1 50
  • PWM2 51
  • PWM3 52
  • PWM4 53
  • PWM5 54
  • PWM6 55
  • PWM7 56
  • PWM8 57

In addition the 4 pins on the servo rail marked CAP1 to CAP4 can be used as GPIOs. These are available as GPIOs in ArduPilot using the following GPIO numbers:

  • CAP1 58
  • CAP2 59
  • CAP3 60
  • CAP4 61

Analog inputs

The Pixhawk4-Mini has 4 analog inputs

  • ADC Pin0 -> Battery Voltage
  • ADC Pin1 -> Battery Current Sensor
  • ADC Pin10 -> ADC 5V Sense
  • ADC Pin11 -> ADC 3.3V Sense

Connectors

Unless noted otherwise all connectors are JST GH

TELEM port

Pin Signal Volt
1 (red) VCC +5V
2 (blk) TX (OUT) +3.3V
3 (blk) RX (IN) +3.3V
4 (blk) CTS +3.3V
5 (blk) RTS +3.3V
6 (blk) GND GND

GPS port

Pin Signal Volt
1 (red) VCC +5V
2 (blk) SERIAL3 TX (OUT) +3.3V
3 (blk) SERIAL3 RX (IN) +3.3V
4 (blk) SCL +3.3 (pullups)
5 (blk) SDA +3.3 (pullups)
6 (blk) SafetyButton +3.3V
7 (blk) SafetyLED +3.3V
8 (blk) VDD 3.3 (OUT) +3.3V
9 (blk) Buzzer +3.3V
10 (blk) GND GND

TELEM2 & I2CB port

Pin Signal Volt
1 (red) VCC +5V
2 (blk) TX (OUT) +3.3V
3 (blk) RX (IN) +3.3V
4 (blk) SCL I2C2 +3.3V
5 (blk) SDA I2C2 +3.3V
6 (blk) GND GND

POWER1

Pin Signal Volt
1 (red) VCC +5V
2 (red) VCC +5V
3 (blk) CURRENT up to +3.3V
4 (blk) VOLTAGE up to +3.3V
5 (blk) GND GND
6 (blk) GND GND

RCIN port

Pin Signal Volt
1 (red) VCC +5V
2 (blk) RCIN (IN) +3.3V
3 (blk) RSSI (IN) +3.3V
4 (blk) VDD3.3 +3.3V
5 (blk) GND GND

Debug

The Pixhawk4 supports SWD debugging on the debug port .. raw:: html

<table border=”1” class=”docutils”> <tbody> <tr> <th>Pin </th> <th>Signal </th> <th>Volt </th> </tr> <tr> <td>1 (red)</td> <td>FMU VDD 3.3</td> <td>+3.3V</td> </tr> <tr> <td>2 (blk)</td> <td>UART TX Debug (OUT)</td> <td>+3.3V</td> </tr> <tr> <td>3 (blk)</td> <td>UART RX Debug (IN)</td> <td>+3.3V</td> </tr> <tr> <td>4 (blk)</td> <td>SWDIO</td> <td>+3.3V</td> </tr> <tr> <td>5 (blk)</td> <td>SWCLK</td> <td>+3.3V</td> </tr> <tr> <td>6 (blk)</td> <td>GND</td> <td>GND</td> </tr> </tbody> </table>

Loading Firmware

The board comes pre-installed with an ArduPilot compatible bootloader, allowing the loading of xxxxxx.apj firmware files with any ArduPilot compatible ground station.

Firmware for this board can be found here in sub-folders labeled “PH4-mini”.

Acknowledgements

Thanks to [PX4](https://docs.px4.io/en/flight_controller/pixhawk4_mini.html) for images used under the [CC-BY 4.0 license](https://creativecommons.org/licenses/by/4.0/)