added read_PWM.py

raspberry_pi/read_PWM.py

@@ -0,0 +1,133 @@
+#!/usr/bin/env python
+
+# read_PWM.py
+# 2015-12-08
+# Public Domain
+
+import time
+import pigpio # http://abyz.co.uk/rpi/pigpio/python.html
+
+class reader:
+   """
+   A class to read PWM pulses and calculate their frequency
+   and duty cycle.  The frequency is how often the pulse
+   happens per second.  The duty cycle is the percentage of
+   pulse high time per cycle.
+   """
+   def __init__(self, pi, gpio, weighting=0.0):
+      """
+      Instantiate with the Pi and gpio of the PWM signal
+      to monitor.
+
+      Optionally a weighting may be specified.  This is a number
+      between 0 and 1 and indicates how much the old reading
+      affects the new reading.  It defaults to 0 which means
+      the old reading has no effect.  This may be used to
+      smooth the data.
+      """
+      self.pi = pi
+      self.gpio = gpio
+
+      if weighting < 0.0:
+         weighting = 0.0
+      elif weighting > 0.99:
+         weighting = 0.99
+
+      self._new = 1.0 - weighting # Weighting for new reading.
+      self._old = weighting       # Weighting for old reading.
+
+      self._high_tick = None
+      self._period = None
+      self._high = None
+
+      pi.set_mode(gpio, pigpio.INPUT)
+
+      self._cb = pi.callback(gpio, pigpio.EITHER_EDGE, self._cbf)
+
+   def _cbf(self, gpio, level, tick):
+
+      if level == 1:
+
+         if self._high_tick is not None:
+            t = pigpio.tickDiff(self._high_tick, tick)
+
+            if self._period is not None:
+               self._period = (self._old * self._period) + (self._new * t)
+            else:
+               self._period = t
+
+         self._high_tick = tick
+
+      elif level == 0:
+
+         if self._high_tick is not None:
+            t = pigpio.tickDiff(self._high_tick, tick)
+
+            if self._high is not None:
+               self._high = (self._old * self._high) + (self._new * t)
+            else:
+               self._high = t
+
+   def frequency(self):
+      """
+      Returns the PWM frequency.
+      """
+      if self._period is not None:
+         return 1000000.0 / self._period
+      else:
+         return 0.0
+
+   def pulse_width(self):
+      """
+      Returns the PWM pulse width in microseconds.
+      """
+      if self._high is not None:
+         return self._high
+      else:
+         return 0.0
+
+   def duty_cycle(self):
+      """
+      Returns the PWM duty cycle percentage.
+      """
+      if self._high is not None:
+         return 100.0 * self._high / self._period
+      else:
+         return 0.0
+
+   def cancel(self):
+      """
+      Cancels the reader and releases resources.
+      """
+      self._cb.cancel()
+
+if __name__ == "__main__":
+
+   import time
+   import pigpio
+   import read_PWM
+
+   PWM_GPIO = 4
+   RUN_TIME = 60.0
+   SAMPLE_TIME = 2.0
+
+   pi = pigpio.pi()
+
+   p = read_PWM.reader(pi, PWM_GPIO)
+
+   start = time.time()
+
+   while (time.time() - start) < RUN_TIME:
+
+      time.sleep(SAMPLE_TIME)
+
+      f = p.frequency()
+      pw = p.pulse_width()
+      dc = p.duty_cycle()
+
+      print("f={:.1f} pw={} dc={:.2f}".format(f, int(pw+0.5), dc))
+
+   p.cancel()
+
+   pi.stop()
+