Add simple Brickpi3 example (#50)

* Add simple Brickpi3 example

* newine

* minor updates

* Update brickpi3-motor-and-sensor.py

`set_device` on output port is not supported

Co-authored-by: David Lechner <david@pybricks.com>

Author: WasabiFan

platform/brickpi3-motor-and-sensor.py

@@ -0,0 +1,38 @@
+#!/usr/bin/env python3
+
+"""
+The Brickpi3 doesn't support auto-detecting motors and sensors. To use devices
+connected to the input ports, you must specify what type of device it is.
+Output ports are pre-configured as NXT Large motors and do not need to be
+configured manually.
+"""
+
+from time import sleep
+from ev3dev2 import list_devices
+from ev3dev2.port import LegoPort
+from ev3dev2.motor import OUTPUT_A, LargeMotor, SpeedPercent
+from ev3dev2.sensor import INPUT_1
+from ev3dev2.sensor.lego import UltrasonicSensor
+
+p1 = LegoPort(INPUT_1)
+# http://docs.ev3dev.org/projects/lego-linux-drivers/en/ev3dev-stretch/brickpi3.html#brickpi3-in-port-modes
+p1.mode = 'ev3-uart'
+# http://docs.ev3dev.org/projects/lego-linux-drivers/en/ev3dev-stretch/sensors.html#supported-sensors
+p1.set_device = 'lego-ev3-us'
+
+# allow for some time to load the new drivers
+sleep(0.5)
+
+s = UltrasonicSensor(INPUT_1)
+m = LargeMotor(OUTPUT_A)
+
+print("Running motor...")
+
+while True:
+    dist = s.distance_centimeters
+    if dist < 50:
+        m.on(SpeedPercent(30))
+    else:
+        m.on(SpeedPercent(-30))
+
+    sleep(0.05)