def __init__(self,
spi_device = None,
vref = DEFAULT_VREF,
):
self._spi = CommSPI(device = spi_device)
self.vref = float(vref)
self.resolution = 2**self.BIT_RESOLUTION - 1
self.scale = self.vref/self.resolution
class MCP3008ADC(object):
""" Interface for MCP3008 8-Channel 10-Bit A/D Converters
with SPI Serial Interface.
Hardware mode SPI can be used by specifying 'device'
during initialization or through 'setup_hardware_spi'.
Software mode SPI (bit-banged) can configured using
'setup_software_spi'.
"""
NUM_CHANNELS = 8
MODEL = 'MCP3008'
BIT_RESOLUTION = 10
def __init__(self,
spi_device = None,
vref = DEFAULT_VREF,
):
self._spi = CommSPI(device = spi_device)
self.vref = float(vref)
self.resolution = 2**self.BIT_RESOLUTION - 1
self.scale = self.vref/self.resolution
def setup_hardware_spi(self, device):
""" configure the driver for hardware communications at the port
specified by 'device', i.e. "/dev/spidev0.0"
"""
self._spi.setup_hardware(device)
def setup_software_spi(self, clockpin, mosipin, misopin, cspin, pinmode):
""" setup the GPIO pins to perform software (bit-banged) communications
"""
self._spi.setup_software(clockpin, mosipin, misopin, cspin, pinmode)
def read(self, chan, mode = 's'):
""" get the ADC voltage scaled value in specified 'mode':
's': single-ended, chan = IN+, gnd = IN-
'd': differential, for each channel pair
e.g. chan = 0 => CH0 = IN+, CH1 = IN-
chan = 1 => CH0 = IN-, CH1 = IN+
"""
raw_val = self.read_raw(chan=chan,mode=mode)
V = raw_val*self.scale
return V
def read_raw(self, chan, mode = 's'):
""" get the raw ADC value in specified 'mode':
's': single-ended, chan = IN+, gnd = IN-
'd': differential, for each channel pair
e.g. chan = 0 => CH0 = IN+, CH1 = IN-
chan = 1 => CH0 = IN-, CH1 = IN+
"""
if not chan in range(self.NUM_CHANNELS):
raise ValueError, "'chan' must be in %r" % range(self.NUM_CHANNELS)
#command byte is (sgl/diff,D2,D1,D0,X,X,X,X)
cmd = None
if mode == 's':
cmd = 1 << 7 #single-ended bit
elif mode == 'd':
cmd = 0 #differential, null bit
else:
raise ValueError, "mode must be 's' (or 'diff'"
cmd |= chan << 4 #D2,D1,D0
raw_val = self._run_transaction(cmd)
return raw_val
def _run_transaction(self, cmd):
bytes_out = bytearray()
bytes_out.append(0x01) #start bit
#command byte is (sgl/diff,D2,D1,D0,X,X,X,X)
bytes_out.append(cmd)
#extra byte to receive data
bytes_out.append(0)
#do transmit/receive
bytes_in = self._spi.transfer(bytes_out)
#data is in 2nd and 3rd bytes (?,?,?,?,?,0,B9,B8), (B7,B6,B5,B4,B3,B2,B1,B0)
#print " ".join(map(bin,bytes_in))
val = (bytes_in[1] & 0b11) << 8
val += bytes_in[2]
return val
