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Camera relay ON value
RELAY10_DEFAULT
RELAY10_FUNCTION
RELAY10_INVERTED
RELAY10_PIN
RELAY11_DEFAULT
RELAY11_FUNCTION
RELAY11_INVERTED
RELAY11_PIN
RELAY12_DEFAULT
RELAY12_FUNCTION
RELAY12_INVERTED
RELAY12_PIN
RELAY13_DEFAULT
RELAY13_FUNCTION
RELAY13_INVERTED
RELAY13_PIN
RELAY14_DEFAULT
RELAY14_FUNCTION
RELAY14_INVERTED
RELAY14_PIN
RELAY15_DEFAULT
RELAY15_FUNCTION
RELAY15_INVERTED
RELAY15_PIN
RELAY16_DEFAULT
RELAY16_FUNCTION
RELAY16_INVERTED
RELAY16_PIN
RELAY1_DEFAULT
RELAY1_FUNCTION
RELAY1_INVERTED
RELAY1_PIN
RELAY2_DEFAULT
RELAY2_FUNCTION
RELAY2_INVERTED
RELAY2_PIN
RELAY3_DEFAULT
RELAY3_FUNCTION
RELAY3_INVERTED
RELAY3_PIN
RELAY4_DEFAULT
RELAY4_FUNCTION
RELAY4_INVERTED
RELAY4_PIN
RELAY5_DEFAULT
RELAY5_FUNCTION
RELAY5_INVERTED
RELAY5_PIN
RELAY6_DEFAULT
RELAY6_FUNCTION
RELAY6_INVERTED
RELAY6_PIN
RELAY7_DEFAULT
RELAY7_FUNCTION
RELAY7_INVERTED
RELAY7_PIN
RELAY8_DEFAULT
RELAY8_FUNCTION
RELAY8_INVERTED
RELAY8_PIN
RELAY9_DEFAULT
RELAY9_FUNCTION
RELAY9_INVERTED
RELAY9_PIN

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Full Parameter PDF

Overview

The RELAY parameter group configures the Digital Relay subsystem. Relays are simple On/Off (3.3V/5V digital) switches used to control external hardware that does not require a PWM signal.

ArduPilot supports up to 6 standard relays (and more in some versions) that can be mapped to any GPIO-capable pin on the flight controller.

Key Concepts

1. Relay Assignment (`RELAYx_PIN`)

Maps a physical pin on the flight controller to a logical relay ID.

RELAY1_PIN: The GPIO ID of the first relay (e.g., 50 for AUX 1).
Disabled (-1): The relay is not active.

2. Logic Polarity (`RELAYx_INVERTED`)

Defines whether "On" is High (3.3V) or Low (0V).

0 (Normal): On = High, Off = Low.
1 (Inverted): On = Low, Off = High.

3. Default State (`RELAYx_DEFAULT`)

Defines the state of the relay immediately after the autopilot boots up.

0: Off.
1: On.
2: No change (Maintain state across reboots if possible).

Parameter Breakdown

RELAY_ON: (Legacy/Global) Global command to toggle.
RELAY1_FUNCTION: Sets the purpose of the relay (e.g., Relay, Ignition, Brush).

Integration Guide

Select Pin: Identify an AUX pin you wish to use.
GPIO Mask: Ensure that pin is enabled in BRD_PWM_COUNT or GPIO_MASK (depending on firmware).
Config: Set RELAY1_PIN to the pin ID.
Control: Map an RC channel to Relay 1 (RC Option 33) to toggle it with a switch.

Developer Notes

Library: libraries/AP_Relay.
Capacity: Useful for controlling lights, smoke systems, camera shutters, or high-power battery isolation contactors.

RELAY_ON: Camera relay ON value

Description

This sets whether the relay goes high or low when it triggers. Note that you should also set RELAY_DEFAULT appropriately for your camera.

Values

Value	Meaning
0	Low (Ground)
1	High (3.3V or 5V)

Default: 1

Description

This parameter configures the electrical signal logic used to trigger a camera via a relay.

Usage: Set this to match your camera's shutter release requirement. Most cameras trigger on a transition.
Function: When the "Take Photo" command is issued, the assigned relay pin will switch to the level defined here for the duration set in CAM_DURATION.

Source Code

ardupilot/libraries/AP_Camera/AP_Camera_Params.cpp

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RELAY10_DEFAULT

Relay default state

Default (float

Range null

Relay default state

Note: This parameter functions identically to RELAY1_DEFAULT.

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Relay function

Note: This parameter functions identically to RELAY1_FUNCTION.

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RELAY10_INVERTED

Relay invert output signal

Default false

Range null

Relay invert output signal

Note: This parameter functions identically to RELAY1_INVERTED.

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Relay pin

Note: This parameter functions identically to RELAY1_PIN.

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RELAY11_DEFAULT

Relay default state

Default (float

Range null

Relay default state

Note: This parameter functions identically to RELAY1_DEFAULT.

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Relay function

Note: This parameter functions identically to RELAY1_FUNCTION.

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RELAY11_INVERTED

Relay invert output signal

Default false

Range null

Relay invert output signal

Note: This parameter functions identically to RELAY1_INVERTED.

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Relay pin

Note: This parameter functions identically to RELAY1_PIN.

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RELAY12_DEFAULT

Relay default state

Default (float

Range null

Relay default state

Note: This parameter functions identically to RELAY1_DEFAULT.

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Relay function

Note: This parameter functions identically to RELAY1_FUNCTION.

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RELAY12_INVERTED

Relay invert output signal

Default false

Range null

Relay invert output signal

Note: This parameter functions identically to RELAY1_INVERTED.

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Relay pin

Note: This parameter functions identically to RELAY1_PIN.

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RELAY13_DEFAULT

Relay default state

Default (float

Range null

Relay default state

Note: This parameter functions identically to RELAY1_DEFAULT.

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Relay function

Note: This parameter functions identically to RELAY1_FUNCTION.

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RELAY13_INVERTED

Relay invert output signal

Default false

Range null

Relay invert output signal

Note: This parameter functions identically to RELAY1_INVERTED.

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Relay pin

Note: This parameter functions identically to RELAY1_PIN.

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RELAY14_DEFAULT

Relay default state

Default (float

Range null

Relay default state

Note: This parameter functions identically to RELAY1_DEFAULT.

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Relay function

Note: This parameter functions identically to RELAY1_FUNCTION.

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RELAY14_INVERTED

Relay invert output signal

Default false

Range null

Relay invert output signal

Note: This parameter functions identically to RELAY1_INVERTED.

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Relay pin

Note: This parameter functions identically to RELAY1_PIN.

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RELAY15_DEFAULT

Relay default state

Default (float

Range null

Relay default state

Note: This parameter functions identically to RELAY1_DEFAULT.

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Relay function

Note: This parameter functions identically to RELAY1_FUNCTION.

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RELAY15_INVERTED

Relay invert output signal

Default false

Range null

Relay invert output signal

Note: This parameter functions identically to RELAY1_INVERTED.

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Relay pin

Note: This parameter functions identically to RELAY1_PIN.

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RELAY16_DEFAULT

Relay default state

Default (float

Range null

Relay default state

Note: This parameter functions identically to RELAY1_DEFAULT.

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Relay function

Note: This parameter functions identically to RELAY1_FUNCTION.

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RELAY16_INVERTED

Relay invert output signal

Default false

Range null

Relay invert output signal

Note: This parameter functions identically to RELAY1_INVERTED.

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Relay pin

Note: This parameter functions identically to RELAY1_PIN.

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RELAY1_DEFAULT

Relay Default State (Instance 1)

Default 0

Range 0 1

Relay Default State (RELAY1_DEFAULT)

Description

RELAY1_DEFAULT defines the "Power-On" state of the first relay output.

This is important for safety and automation. For example, if Relay 1 is connected to a camera power supply, you might want it to default to ON (1) so the camera starts recording immediately upon power-up. If it is connected to a loud siren or a high-voltage igniter, you would set it to OFF (0) to prevent accidental activation.

0: OFF. The relay starts in the deactivated state.
1: ON. The relay starts in the activated state.

Tuning & Behavior

Default: 0.
Logic Link: This value is applied immediately when the autopilot initializes.
Note: If RELAY1_INVERTED is enabled, the physical output state will be flipped relative to this setting.

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RELAY1_FUNCTION

Relay Function (Instance 1)

Default 0

Range 0 100

Relay Function (RELAY1_FUNCTION)

Description

RELAY1_FUNCTION defines the "Job" of the first relay output.

Unlike physical PWM outputs which are usually used for motors and servos, Relays are simple digital ON/OFF switches. This parameter tells the autopilot what internal logic should control this switch.

Common Values

0: None. Relay is disabled.
1: Relay. Manual control via MAVLink or auxiliary switch.
2: Ignition. Controlled by the Internal Combustion Engine (ICE) library.
3: Parachute. Triggered when a crash is detected.
4: Camera. Triggered by the camera shutter logic.

Tuning & Behavior

Default: 0.
Note: If you want to use the relay for a custom purpose (like turning on LED lights via a transmitter switch), set this to 1 (Relay) and assign an RC channel to that relay instance.

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RELAY1_INVERTED

Relay Inversion (Instance 1)

Default 0

Range 0 1

Relay Inversion (RELAY1_INVERTED)

Description

RELAY1_INVERTED calibrates the autopilot for your specific relay hardware.

Different relay modules have different "Trigger" requirements. Some turn ON when given a 3.3V signal (Active-High), while others turn ON when the signal is pulled to Ground (Active-Low).

0: Normal. Active-High (Standard).
1: Inverted. Active-Low.

Tuning & Behavior

Calibration: If your relay stays ON when you command it OFF (and vice versa), toggle this parameter.

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RELAY1_PIN

Relay Pin (Instance 1)

Default -1

Range -1 103

Relay Pin (RELAY1_PIN)

Description

RELAY1_PIN tells the autopilot which digital connector on the flight controller is wired to the relay hardware.

-1: Disabled (No physical pin assigned).
0-103: Physical GPIO pin number.

Tuning & Behavior

Setup: Refer to your flight controller's "GPIOs" documentation to find the correct number for the pin you are using.
Hardware Constraint: Standard servo outputs on many Pixhawk-style boards cannot be used as relays unless they are first "freed" by setting their SERVOx_FUNCTION to -1.

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