The rangefinder's input pin is not set, or cannot be used

What ArduPilot says:

• RNGFNDN_PIN=N, set SERVON_FUNCTION=-1
• RNGFNDN_PIN not set
• RNGFNDN_PIN=N invalid

An analog rangefinder (RNGFNDn_TYPE 1) or a PWM one (5 or 22) is read through a pin of the flight controller, named by RNGFNDn_PIN. “not set” means the parameter is still -1. A PWM sensor also needs the pin to be a free GPIO (a general-purpose pin): “invalid” means this board has no pin with that number, and “set SERVOn_FUNCTION=-1” means the pin is a servo/motor output that still works as an output.

What to do, most likely first

1. The sensor is not analog or PWM at all: a serial or I2C lidar was given the wrong type.

   CheckTypes 1, 5 and 22 are only for sensors that give a voltage or a pulse width on one signal wire.

   FixSet RNGFNDn_TYPE to your sensor's own type (20 for a TFmini or TF-Luna on a UART) and reboot.

2. RNGFNDn_PIN was never set.

   FixSet RNGFNDn_PIN to the pin the signal wire is on: an analog input number for an analog sensor, a GPIO number for a PWM one. Your board's ArduPilot documentation page lists both.

3. The pin is one of the servo/motor outputs and is still set up as an output.

   CheckThe message names the output: “set SERVO9_FUNCTION=-1” is output 9.

   FixSet that SERVOn_FUNCTION to -1 (GPIO) and reboot: outputs become GPIO pins only at start-up. Nothing else (a motor, a servo) may be wired to that output.

4. The pin number does not exist on this board: it was copied from another board's parameters.

   FixUse a pin number from your own board's documentation; the numbers differ from board to board.

Parameters to look at

Where to do it:Board & Wiring Planner