Servo Pi Library for C++

C++ Library to use with Servo Pi Raspberry Pi development board.

The example C++ files can be found in /ABElectronics_CPP_Libraries/ServoPi/demos

Downloading and Installing the library

To download to your Raspberry Pi type in the terminal:

git clone https://github.com/abelectronicsuk/ABElectronics_CPP_Libraries.git

Classes:

PWM(uint8_t address, uint8_t use_oe_pin)

The PWM class provides control over the pulse-width modulation outputs on the PCA9685 controller. Methods include setting the frequency and duty cycle for each channel.

Note: The PWM class was previously called ServoPi.

Parameter: address - I2C address. Defaults to 0x40
Optional Parameter: use_oe_pin - Enable the Output Enable pin on the GPIO port. 1 = enable, 0 = disable. Defaults to false.

Methods:

set_pwm_freq(double freq, uint8_t calibration=0) 

Set the PWM frequency
Parameter: freq - required frequency
Optional Parameter: calibration - optional integer value to offset oscillator errors. Defaults to 0
Returns: null

set_pwm(uint8_t channel, uint16_t on, uint16_t off) 

Set the output for single channels
Parameter: channel - 1 to 16
Parameter: on - time period 0 to 4095
Parameter: off - time period 0 to 4095.
Total on-time and off-time can not exceed 4095
Returns: null

set_pwm_on_time(uint8_t channel, uint16_t on_time)

Set the output on time for a single channel
Parameter: channel - 1 to 16
Parameter: on_time - time period 0 to 4095
Returns: null

set_pwm_off_time(uint8_t channel, uint16_t off_time)

Set the output off time for a single channel
Parameter: channel - 1 to 16
Parameter: off_time - time period 0 to 4095
Returns: null

get_pwm_on_time(uint8_t channel)

Get the output on time for a single channel
Parameter: channel - 1 to 16
Returns: (uint16_t) on time

get_pwm_off_time(uint8_t channel)

Get the output off time for a single channel
Parameter: channel - 1 to 16
Returns: (uint16_t) off time

set_all_pwm(uint16_t on, uint16_t off) 

Set the output on all channels
Parameter: on - time period
Parameter: off - time period 0 to 4095.
Total on-time and off-time can not exceed 4095
Returns: null

output_disable()

Disable the output via the OE pin
Parameter: null
Returns: null

output_enable()

Enable the output via the OE pin
Parameter: null
Returns: null

set_allcall_address(uint8_t allcalladdress)

Set the I2C address for the All Call function
Parameter: address
Returns: null

enable_allcall_address()

Enable the I2C address for the All Call function
Returns: null

disable_allcall_address()

Disable the I2C address for the All Call function
Returns: null

sleep()

Puts the PCA9685 PWM controller into a sleep state.
Returns: null

wake()

Wakes the PCA9685 PWM controller from its sleep state.
Returns: null

is_sleeping()

Returns if the PCA9685 PWM controller is in its sleep state.
Parameter: null
Returns: (bool) true = Is sleeping, false = Is awake.

invert_output(state)

Inverts the outputs on all PWM channels.
Parameter: True = inverted, False = non-inverted
Returns: null

invert_output(bool state)

Invert the PWM output on all channels
Parameter: state = true = inverted, false = non-inverted
Returns: null

set_address(uint8_t address)

Set the I2C address
Parameter: address = i2c address
Returns: null

get_address()

Get the I2C address
Returns: (uint8_t) i2c address

enable_oe_pin()

Enable the Output Enable Pin on the GPIO header
Returns: null

Class: Servo

The Servo class provides functions for controlling the position of servo motors commonly used on radio control models and small robots. The Servo class initialises with a default frequency of 50Hz and low and high limits of 1ms and 2ms.

Initialise with the I2C address for the Servo Pi.

Servo(uint8_t address, double low_limit, double high_limit, bool reset, bool use_oe_pin)

Parameter: address - i2c address for the ServoPi board, defaults to 0x40
Optional Parameter: low_limit - Pulse length in milliseconds for the lower servo limit. (default = 1.0ms)
Optional Parameter: high_limit - Pulse length in milliseconds for the upper servo limit. (default = 2.0ms)
Optional Parameter: reset - true: reset the servo controller and turn off all channels. false: initialise with existing servo positions and frequency. (default = true)
Optional Parameter: use_oe_pin - true = Enable the Output Enable pin on the GPIO port. false = Output Enable pin not used. Defaults to true.

Methods:

move(channel, position, steps=250) 

Set the servo position
Parameter: channel - 1 to 16
Parameter: position - value between 0 and the maximum number of steps.
Optional Parameter: steps - The number of steps between the low and high servo limits. This is preset at 250 but can be any number between 0 and 4095. On a typical RC servo a step value of 250 is recommended.
Returns: null

get_position(channel, steps=250) 

Get the servo position
Parameter: channel - 1 to 16
Optional Parameter: steps - The number of steps between the low and high servo limits. This is preset at 250 but can be any number between 0 and 4095. On a typical RC servo, a step value of 250 is recommended.
Returns: (uint16_t) position - value between 0 and the maximum number of steps. Due to rounding errors when calculating the position, the returned value may not be the same as the set value.

set_low_limit(low_limit, channel)

Set the pulse length for the lower servo limits. Typically around 1 ms.
Warning: Setting the pulse limit below 1 ms may damage your servo.
Parameter: low_limit - Pulse length in milliseconds for the lower servo limit.
Optional Parameter: channel - The channel for which the low limit will be set. If this value is omitted or set to 0 the low limit will be set for all channels.
Returns: null

set_high_limit(high_limit, channel)

Set the pulse length for the upper servo limits. Typically around 2ms. Warning: Setting the pulse limit above 2ms may damage your servo.
Parameter: high_limit - Pulse length in milliseconds for the upper servo limit.
Optional Parameter: channel - The channel for which the upper limit will be set.
If this value is omitted the upper limit will be set for all channels.
Returns: null

set_frequency(freq, calibration) 

Set the PWM frequency
Parameter: freq - required frequency for the servo.
Optional Parameter: calibration - optional integer value to offset oscillator errors. Defaults to 0
Returns: null

output_disable()

Disable the output via the OE pin
Parameter: null
Returns: null

output_enable()

Enable the output via the OE pin
Parameter: null
Returns: null

offset_enable()

Enable pulse offsets.
This will set servo pulses to be staggered across the channels to reduce surges in the current draw.
Parameter: null
Returns: null

offset_disable()

Disable pulse offsets.
This will set all servo pulses to start at the same time.
Parameter: null
Returns: null

sleep()

Put the device into a sleep state.
Parameter: null
Returns: null

wake()

Wake the device from its sleep state.
Parameter: null
Returns: null

is_sleeping()

Check the sleep status of the device.
Parameter: null
Returns: (bool) true = Is sleeping, false = Is awake.

Usage

PWM Class

To use the Servo Pi PWM class in your code you must first import the class: from ServoPi import PWM Next, you must initialise the PWM object: pwm = PWM(0x40) Set the PWM frequency to 200 Hz and enable the output pwm.set_pwm_freq(200) pwm.output_enable() Set the pulse width of channel 1 to 1024 or 25% duty cycle pwm.set_pwm(1, 0, 1024)

Servo Class

To use the Servo Pi Servo class in your code you must first import the class:

from ServoPi import Servo

Next, you must initialise the Servo object:

servo = Servo(0x40)

Set PWM frequency to 50 Hz

servo.set_frequency(50)  

Move the servo on channel 1 to position 125 out of 250 steps

servo.move(1, 125, 250)