Servo Motor Driver

High-level driver for servo motors. More...

Detailed Description

High-level driver for servo motors.

Usage

Select a flavor of the driver, e.g. USEMODULE += servo_pwm for PWM based servo driver or USEMODULE += servo_timer for periph_timer_periodic based servo driver to use. Typically, the PWM implementation is the preferred one, but some MCU (e.g. nRF52xxx) cannot configure the PWM peripheral to run anywhere close to the 50 Hz to 100 Hz required.

In addition, you many need to extend or adapt servo_params and, depending on the selected implementation, servo_pwm_params or servo_timer_params to match your hardware configuration.

The test application in tests/drivers/servo can serve as starting point for users.

Modules
	PWM based servo driver
	SAUL integration of the servo driver
	periph_timer_periodic based servo driver

Files
file	servo.h
	High-level driver for easy handling of servo motors.
file	servo_params.h
	Default configuration for servo devices.

Data Structures
struct	servo_pwm_params_t
	PWM configuration parameters for a servos. More...
struct	servo_timer_ctx_t
	Memory needed for book keeping when using periph_timer_periodic based servo driver. More...
struct	servo_timer_params_t
	Timer configuration parameters for a servos. More...
struct	servo_params_t
	Configuration parameters for a servo. More...
struct	servo
	Servo device state. More...

Macros
#define	SERVO_TIMER_MAX_CHAN   4
	In case the servo_timer backend is used to driver the servo, this is the highest channel number usable by the driver.

Typedefs
typedef struct servo	servo_t
	Servo device state.

Functions
int	servo_init (servo_t *dev, const servo_params_t *params)
	Initialize servo.
void	servo_set (servo_t *dev, uint8_t pos)
	Set the servo motor to a specified position.

Variables
const saul_driver_t	servo_saul_driver
	The SAUL adaption driver for servos.
servo_timer_ctx_t	servo_timer_default_ctx
	Default timer context.

Macro Definition Documentation

SERVO_TIMER_MAX_CHAN

#define SERVO_TIMER_MAX_CHAN   4

In case the servo_timer backend is used to driver the servo, this is the highest channel number usable by the driver.

Note

To drive n servos, n + 1 timer channels are required. Hence, this must be at least 2

Trimming this down safes a small bit of RAM: Storage for one pointer is wasted on every servo that could be controlled by a timer but is not actually used.

Definition at line 66 of file servo.h.

Typedef Documentation

servo_t

typedef struct servo servo_t

Servo device state.

Definition at line 92 of file servo.h.

Function Documentation

servo_init()

int servo_init	(	servo_t *	dev,
		const servo_params_t *	params
	)

Initialize servo.

Parameters

[out]	dev	Device handle to initialize
[in]	params	Parameters defining the PWM configuration

Return values

0	Success
<0	Failure (as negative errno code to indicate cause)

servo_set()

void servo_set	(	servo_t *	dev,
		uint8_t	pos
	)

Set the servo motor to a specified position.

The position of the servo is specified in the fraction of maximum extension, with 0 being the lowest extension (e.g. on an 180° servo it would be at -90°) and UINT8_MAX being the highest extension (e.g. +90° on that 180° servo).

Parameters

[in]	dev	the servo to set
[in]	pos	the extension to set

Note: 8 bit of resolution may seem low, but is indeed more than high enough for any practical PWM based servo. For higher precision, stepper motors would be required.