Control the Sphero RVR over the serial port, using Circuitpython
The packages are well documented by @emwdx in his code for drive_to_position
:
# Set up the serial port on the board
uart = busio.UART(board.TX, board.RX, baudrate=115200)
# This function takes in an angle, a pair of x and y coordinates, and a speed target to use for the RVR.
def drive_to_position_si(yaw_angle, x, y, speed):
# This sets up the list of bytes needed for this command to be sent to the RVR through the serial port.
SOP = 0x8d # Always the start byte for a command to the RVR
FLAGS = 0x06 # This tells the RVR to ignore the target and source ID,
# and that this command expects a response only if there are errors.
TARGET_ID = 0x0e
SOURCE_ID = 0x0b
DEVICE_ID = 0x16 # The drive system ID is 0x16
COMMAND_ID = 0x38 # The drive_to_position_si command has ID of 38
SEQ = 0x01 # The sequence value is arbitrarily 1. We aren't using the sequence capability here.
EOP = 0xD8 # The final byte in the command is 0xD8
# The command expects four float values for yaw angle, x coordinate, y coordinate, and speed.
# This lets you use decimal values.
# The lines below convert the float values to a set of four bytes representing each value.
yaw_angle = bytearray(struct.pack('>f', yaw_angle))
x = bytearray(struct.pack('>f', x))
y = bytearray(struct.pack('>f', y))
speed = bytearray(struct.pack('>f', speed))
# The command has a flags byte that lets you set different attributes for how the robot moves
# between the positions. Check out page 12 of the SpheroRVRControlSystem manual for the details.
flags = bytearray(struct.pack('B', 0))
# Now we build the command packet byte by byte. First the first five bytes:
output_packet = [SOP, FLAGS, DEVICE_ID, COMMAND_ID, SEQ]
# Now the bytes for the flags
output_packet.extend(yaw_angle)
output_packet.extend(x)
output_packet.extend(y)
output_packet.extend(speed)
output_packet.extend(flags)
# And the checksum byte which does some math with the sum of the previous
# bytes in the command, and finally the end of packet byte.
output_packet.extend([~((sum(output_packet) - SOP) % 256) & 0x00FF,EOP])
# Now that the command is complete, return the command as an array of bytes.
return bytearray(output_packet)
# END OF DRIVE_TO_POSITION_SI