Merge pull request #2 from srobo/ultrasound

Add ultrasound function

Makefile

@@ -1,4 +1,4 @@
-FW_VER=1
+FW_VER=2
 DEV=/dev/ttyACM0
 
 CC=avr-gcc

src/ruggeduino.cpp

@@ -14,6 +14,8 @@ void setup() {
 }
 
 int read_pin() {
+  // Convert the ASCII character to a pin number.
+  // a -> 0, b -> 1, c -> 2, etc.
   while (!Serial.available());
   int pin = Serial.read();
   return (int)(pin - 'a');
@@ -47,6 +49,33 @@ void command_mode(int mode) {
   pinMode(pin, mode);
 }
 
+void command_ultrasound() {
+  int pulse = read_pin();
+  int echo = read_pin();
+
+  // config pins to correct modes
+  pinMode(pulse, OUTPUT);
+  pinMode(echo, INPUT);
+
+  // provide pulse to trigger reading
+  digitalWrite(pulse, LOW);
+  delayMicroseconds(2);
+  digitalWrite(pulse, HIGH);
+  delayMicroseconds(5);
+  digitalWrite(pulse, LOW);
+
+  // measure the echo time on the echo pin
+  int duration = pulseIn(echo, HIGH, 60000);
+  Serial.print(microsecondsToMm(duration));
+}
+
+long microsecondsToMm(long microseconds) {
+  // The speed of sound is 340 m/s or 29 microseconds per centimeter.
+  // The ping travels out and back, so to find the distance we need half
+  // 10 x (us / 29 / 2)
+  return (5 * microseconds / 29);
+}
+
 void loop() {
   // Fetch all commands that are in the buffer
   while (Serial.available()) {
@@ -74,6 +103,9 @@ void loop() {
       case 'p':
         command_mode(INPUT_PULLUP);
         break;
+      case 'u':
+        command_ultrasound();
+        break;
       case 'v':
         Serial.print("SRduino:");
         Serial.print(FW_VER);