diff --git a/README.org b/README.org
index 11534e7..f291374 100644
--- a/README.org
+++ b/README.org
@@ -7,5 +7,5 @@ pip install -r requirements.txt
 
 * Connect to serial port
 #+BEGIN_SRC sh
-sudo picocom /dev/ttyUSB0 -b115200
+picocom /dev/ttyUSB0 -b115200
 #+END_SRC
diff --git a/hcsr04.py b/hcsr04.py
new file mode 100644
index 0000000..2bbcd95
--- /dev/null
+++ b/hcsr04.py
@@ -0,0 +1,77 @@
+import machine, time
+from machine import Pin
+
+__version__ = '0.1.0'
+__author__ = 'Roberto Sánchez'
+__license__ = "Apache License 2.0. https://www.apache.org/licenses/LICENSE-2.0"
+
+class HCSR04:
+    """
+    Driver to use the untrasonic sensor HC-SR04.
+    The sensor range is between 2cm and 4m.
+
+    The timeouts received listening to echo pin are converted to OSError('Out of range')
+
+    """
+    # echo_timeout_us is based in chip range limit (400cm)
+    def __init__(self, trigger_pin, echo_pin, echo_timeout_us=500*2*30):
+        """
+        trigger_pin: Output pin to send pulses
+        echo_pin: Readonly pin to measure the distance. The pin should be protected with 1k resistor
+        echo_timeout_us: Timeout in microseconds to listen to echo pin.
+        By default is based in sensor limit range (4m)
+        """
+        self.echo_timeout_us = echo_timeout_us
+        # Init trigger pin (out)
+        self.trigger = Pin(trigger_pin, mode=Pin.OUT, pull=None)
+        self.trigger.value(0)
+
+        # Init echo pin (in)
+        self.echo = Pin(echo_pin, mode=Pin.IN, pull=None)
+
+    def _send_pulse_and_wait(self):
+        """
+        Send the pulse to trigger and listen on echo pin.
+        We use the method `machine.time_pulse_us()` to get the microseconds until the echo is received.
+        """
+        self.trigger.value(0) # Stabilize the sensor
+        time.sleep_us(5)
+        self.trigger.value(1)
+        # Send a 10us pulse.
+        time.sleep_us(10)
+        self.trigger.value(0)
+        try:
+            pulse_time = machine.time_pulse_us(self.echo, 1, self.echo_timeout_us)
+            return pulse_time
+        except OSError as ex:
+            if ex.args[0] == 110: # 110 = ETIMEDOUT
+                raise OSError('Out of range')
+            raise ex
+
+    def distance_mm(self):
+        """
+        Get the distance in milimeters without floating point operations.
+        """
+        pulse_time = self._send_pulse_and_wait()
+
+        # To calculate the distance we get the pulse_time and divide it by 2
+        # (the pulse walk the distance twice) and by 29.1 becasue
+        # the sound speed on air (343.2 m/s), that It's equivalent to
+        # 0.34320 mm/us that is 1mm each 2.91us
+        # pulse_time // 2 // 2.91 -> pulse_time // 5.82 -> pulse_time * 100 // 582
+        mm = pulse_time * 100 // 582
+        return mm
+
+    def distance_cm(self):
+        """
+        Get the distance in centimeters with floating point operations.
+        It returns a float
+        """
+        pulse_time = self._send_pulse_and_wait()
+
+        # To calculate the distance we get the pulse_time and divide it by 2
+        # (the pulse walk the distance twice) and by 29.1 becasue
+        # the sound speed on air (343.2 m/s), that It's equivalent to
+        # 0.034320 cm/us that is 1cm each 29.1us
+        cms = (pulse_time / 2) / 29.1
+        return cms