Servo Breakout

This is a simple breakout cable for PX4FMU; it provides 4 PWM outputs, serial Rx/Tx for telemetry, PPM and battery voltage sensing.

Parts required:

  • 15-pin DF13 connector shell
  • assorted DF13 jumper wires as described on the PX4 Peripherals page. You can save on jumper wires by cutting the 12“ jumper wires in half and using each half separately.
  • 8×3 0.1”/2.54mm pitch “servo”-style pin block. If you don't have one of these, three rows of 8×1 pins will work too.
  • A small 0.1“/2.54mm prototype board, e.g. the Measure Explorer ME-PB-101SP (a more expensive but nicer Measure Explorer board is available from Sparkfun).

Assemble the jumper wires to the DF13 as shown in the picture below. Use the pinout guide on the PX4FMU page to connect jumper wires to the following pins, in order:

  • GND
  • –skip–
  • –skip–
  • SRV4
  • SRV3
  • SRV2
  • SRV1
  • USART1_TX
  • USART1_RX
  • PPM_INPUT
  • BATTERY_MONITOR
  • –skip–
  • –skip–
  • –skip–
  • VDD_5V

Parts before assembly

Place the 8×3 pins through the board and use some hookup wire to connect all of the ground and power pins together.

Power and Ground

Solder the jumper wires to the signal pins. Pick an ordering that works for you; in this example the serial rx/tx pins are separated from the servo and PWM input pins. If you decide to solder the battery sense wire to your breakout board, be very careful as the voltage on this wire will damage the PX4FMU if it is connected directly to any of the other pins.

Soldering jumper wires

When soldering 0.1” pins, it helps to have a connector (even just a jumper) on the pins to help keep them straight, as otherwise the connector body can easily melt and give you skewed pins.

Soldering, top side

The finished breakout cable. Note that the purple wire is not connected to the board in this case; it will be connected directly to the power distribution board. You can connect a 1kOhm resistor in series with the wire to reduce the risk of damage if the pin is accidentally connected to the wrong place without substantially changing the measured battery voltage.

The ziptie near to the board acts as a strain relief, reducing the risk of fatigue on the wire ends and solder joints. For added reliability, once you have tested the board use hot glue to reinforce the wires at the point they attach to the board, and cover the back side of the connector with a thin layer as well.

The finished breakout cable

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