add sonic measure

Author: iitzex

README.md

@@ -13,18 +13,27 @@ Examples for micropython at NodeMCU
 
 led_on.py : light LED 
         GPIO setting, OUT
+        Pin:D0
 
 flash_key : pushing the flash button will light LED
         GPIO setting, IN, Timer w/ polling 
+        Pin:D3
 
 led_breath.py : make LED light and dim
         software PWM, Timer, w/ delay
         may cause reset w/o correct setting
+        Pin:D0
 
 led_breath_timer.py : make LED light and dim
         software PWM, Timer
         set each period w/ timer
+        Pin:D0
 
 stepper.py : use 28BYJ-48 5V DC stepper
+        Pin:D1, D2, D3, D4
+
+sonic.py : use HC-SR04 to measure distance
+        Pin:D5, D6
+
 
 ```

sonic.py

@@ -0,0 +1,29 @@
+from pyb import Pin
+from time import sleep_ms, sleep_us, ticks_us
+from machine import Timer
+
+D5 = Pin(14, Pin.OUT)
+D6 = Pin(12, Pin.IN)
+Trig = D5
+Echo = D6
+
+def measure():
+    Trig.low()
+    sleep_us(15)
+    Trig.high()
+    sleep_us(15)
+    Trig.low()
+    while(Echo.value() == 0):
+        start = ticks_us()
+    while(Echo.value() == 1):
+        end = ticks_us()
+    duration = end - start
+    dist = 0.03435 * 0.5 * duration
+    print("duration: " + str(duration) + ", " + \
+          "distance: " + str(dist))
+    return dist
+
+tim = Timer(0)
+tim.deinit()
+tim.init(period=200, mode=Timer.PERIODIC, callback=lambda t:measure())
+#