chirp.py

#!/usr/bin/env python
from __future__ import print_function

import smbus, time, sys

class Chirp:
  def __init__(self, bus=1, address=0x20):
    self.bus_num = bus
    self.bus = smbus.SMBus(bus)
    self.address = address
    self.reset()
    self.version()

  def reset(self):
    self.write(0x06)
    time.sleep(1)

  def version(self):
    self.write(0x07)
    ver = self.read()
    print("version", hex(ver))

  def read(self):
    ok = False
    val = None
    count = 0
    while not ok:
      try:
        # sometime reading raises an IOError, i don't know why.
        val = self.bus.read_byte(self.address)
        ok = True
      except IOError:
        time.sleep(0.1)
        count = count + 1
        if count > 5:
          raise
        pass
    return val

  def write(self, reg):
    count = 0
    ok = False
    while not ok:
      try:
        # sometime writing raises an IOError, i don't know why.
        self.bus.write_byte(self.address, reg)
        ok = True
      except IOError, e:
        time.sleep(0.1)
        count = count + 1
        if count > 5:
          print(e)
          # will this just break everything?
          time.sleep(10)

  def get_reg(self, reg):
    # read 2 bytes from register
    val = self.bus.read_word_data(self.address, reg)
    # if the chrip has no data it sends
    # 0xff, use this to re-sync in case we loose values.
    t = self.read()
    while t != 0xff:
      t = self.read()
    # return swapped bytes (they come in wrong order)
    return (val >> 8) + ((val & 0xFF) << 8)

  def cap_sense(self):
    self.get_reg(0)
    while self.get_busy():
      time.sleep(0.1)
    return self.get_reg(0)

  def temp(self):
    return self.get_reg(5)

  def light(self):
    self.reset()
    self.write(3)
    while self.get_busy():
      time.sleep(0.1)
    return self.get_reg(4)

  def get_busy(self):
    self.write(0x09)
    b = self.read()
    # now flush to re-sync
    t = self.read()
    while t != 0xff:
      t = self.read()
    if b > 0:
      return True
    else:
      return False

  def __repr__(self):
    return "<Chirp sensor on bus %d, addr 0x%02x>" % (self.bus_num, self.address)

if __name__ == "__main__":
  addr = 0x20
  bus = 2

  if len(sys.argv) > 1:
    if sys.argv[1].startswith("0x"):
      addr = int(sys.argv[1], 16)
    else:
      addr = int(sys.argv[1])

  if len(sys.argv) > 2:
      bus = int(sys.argv[2])

  chirp = Chirp(bus, addr)

  while True:
    chirp.reset()
    print("cap", chirp.cap_sense())
    chirp.reset()
    print("temp", chirp.temp() / 10.0)
    chirp.reset()
    print("light", chirp.light())
    time.sleep(1)
    print()