added error message if no i2c devices are found

micropython_firmware/main.py

@@ -1,4 +1,5 @@
 import machine
+import sys
 from machine import I2C, Pin
 
 import d1motor
@@ -13,7 +14,9 @@ class Robot:
         d1 = Pin(5)
         d2 = Pin(4)
         i2c = I2C(scl=d1, sda=d2)
-        i2c_addr = i2c.scan()[0]
+        i2c_scan = i2c.scan()
+        if len(i2c_scan) > 0:
+            i2c_addr = i2c_scan[0]
             print("i2c scan = {}".format(i2c_addr))
             print("setting up motors ...")
             self.m1 = d1motor.Motor(0, i2c, address=i2c_addr)
@@ -21,6 +24,9 @@ class Robot:
             self.m1.speed(0)
             self.m2.speed(0)
             print("motor setup complete!")
+        else:
+            print("error: no i2c interfaces found!")
+            sys.exit(1) 
 
         ip = my_ip[0]
         # setup socket for remote control