Arduino API
The Arduino provides a total of 18 pins for either digital input or output (labelled 2 to 13 and A0 to A5), pins A0 to A5 also support analog input.
Digital pins 0 and 1 are reserved and cannot be used.
Accessing the Arduino
The Arduino can be accessed using the arduino property of the Robot
object.
my_arduino = robot.arduino
You can use the GPIO (General Purpose Input/Output) pins for anything, from microswitches to LEDs. GPIO is only available on pins 2 to 13 and A0 to A5 because pins 0 and 1 are reserved for communication with the rest of our kit.
Pin Mode
GPIO pins have different modes. A pin can only have one mode at a time, and some pins aren't compatible with certain modes. These pin modes are represented by an enum which needs to be imported before they can be used.
from sbot import GPIOPinMode
The input modes closely resemble those of an Arduino. More information on them can be found in their docs.
Setting the pin mode
You will need to ensure that the pin is in the correct pin mode before performing an action with that pin. You can read about the possible pin modes below.
robot.arduino.pins[3].mode = GPIOPinMode.INPUT_PULLUP
Digital Input
Digital inputs can be used to check the state of a pin (whether it is high or low). This is useful for connecting something such as a micro-switch.
robot.arduino.pins[4].mode = GPIOPinMode.INPUT
pin_value = robot.arduino.pins[4].digital_value
Some external switches may require a pull up resistor.
GPIOPinMode.INPUT_PULLUP, is the same as INPUT but also enables an internal pull-up
resistor.
robot.arduino.pins[4].mode = GPIOPinMode.INPUT_PULLUP
pin_value = robot.arduino.pins[4].digital_value
Digital Output
Digital outputs can be used to set binary values of 0V or 5V to the pin.
This can be used to turn an LED on and off for example.
robot.arduino.pins[4].mode = GPIOPinMode.OUTPUT
robot.arduino.pins[6].mode = GPIOPinMode.OUTPUT
robot.arduino.pins[4].digital_value = True
robot.arduino.pins[6].digital_value = False
Analog Input
Certain sensors output analog signals rather than digital ones, and so
have to be read differently. The Arduino has six analog inputs, which
are labelled A0 to A5.
Analog signals can have any voltage, while digital signals can only take on one of two voltages. You can read more about digital vs analog signals here.
from sbot import AnalogPins
robot.arduino.pins[AnalogPins.A0].mode = GPIOPinMode.INPUT
pin_value = robot.arduino.pins[AnalogPins.A0].analog_value
The values are the voltages read on the pin, between 0 and 5.
Ultrasound Sensors
You can also measure distance using an ultrasound sensor from the arduino. Ultrasound sensors return the distance of the closest object in mm.
# Trigger pin: 4
# Echo pin: 5
distance_mm = robot.arduino.ultrasound_measure(4, 5)
The ultrasound sensor can measure distances up to 4 metres. If the ultrasound signal has to travel further than 4m, the sensor will timeout and return 0.