Pressure sensor comparison: MPL115A1 and MPL3115A2S

MPL3115A2S_measure.py

from	machine		import	I2C, SPI, Pin, Timer
from	utime		import	sleep, localtime
from	struct		import	unpack
import	os

class MPL3115A2S:
	def __init__( self, i2c, addr = 0xC0 >> 1 ):
		self.i2c		= i2c
		self.addr		= addr
		self.data_ready	= True

		"""
		self.i2c.writeto( self.addr, bytearray( [ 0x26, 0x38 ] ) )
		self.i2c.writeto( self.addr, bytearray( [ 0x13, 0x07 ] ) )
		self.i2c.writeto( self.addr, bytearray( [ 0x26, 0x39 ] ) )
		self.i2c.writeto( self.addr, bytearray( [ 0x26, 0x3B ] ) )
		"""

		self.i2c.writeto( self.addr, bytearray( [ 0x26, 0x00 ] ) )
		self.i2c.writeto( self.addr, bytearray( [ 0x13, 0x07 ] ) )
		self.i2c.writeto( self.addr, bytearray( [ 0x26, 0x01 ] ) )
		self.i2c.writeto( self.addr, bytearray( [ 0x26, 0x03 ] ) )

	def measurement_start( self ):
		pass

	def pressure( self ):
		
		while True:
			self.i2c.writeto( self.addr, bytearray( [ 0x00 ] ), False )	# pointer byte write
			val	= self.i2c.readfrom( self.addr, 1 )
			
			if val[ 0 ] & 0x08:
				break
		
		
		self.i2c.writeto( self.addr, bytearray( [ 0x01 ] ), False )	# pointer byte write
		val	= self.i2c.readfrom( self.addr, 5 )
		
		p	= ((val[ 0 ] << 16) | (val[ 1 ] << 8) | val[ 2 ]) / 6400
		t	= val[ 3 ] + (val[ 4 ] >> 4) / 4

		#print( f"{val[0]:02X} {val[1]:02X} {val[2]:02X}" )

		self.t	= t	
		return p

class MPL115A1:
	def __init__( self, spi, cs ):
		self.spi		= spi
		self.cs			= cs
		self.in_meas	= False
		self.data_ready	= False
		self.timer		= None
		self._get_coeff()
		
	def measurement_start( self ):
		if self.in_meas or self.data_ready:
			return

		self.in_meas	= True

		self._cs_ctrl( 0 )
		self.spi.write( bytearray( [ 0x24, 0x00 ] ) )	
		self._cs_ctrl( 1 )
		"""
		Timer( -1, mode = Timer.ONE_SHOT, period = 3, callback = self._set_ready_flag )
		"""
		if not self.timer:
			self.timer	= Timer( -1 )
		
		self.timer.init( mode = Timer.ONE_SHOT, period = 3, callback = self._set_ready_flag )
		
	def pressure( self ):
		self.measurement_start()
	
		while not self.data_ready:
			pass

		p_adc, t_adc	= self._pressure_temp()
		
		p_comp	= self.a0 + (self.b1 + self.c12 * t_adc) * p_adc + self.b2 * t_adc
	 
		return (p_comp * ((115 - 50) / 1023) + 50) * 10


	def _get_coeff( self ):
		data	= self._insert_zero_bytes( [ 0x88, 0x8A, 0x8C, 0x8E, 0x90, 0x92, 0x94, 0x96 ] )

		self._cs_ctrl( 0 )
		self.spi.write_readinto( data, data )
		self._cs_ctrl( 1 )
		
		self.a0, self.b1, self.b2, self.c12	= unpack( ">hhhh", self._collect_odd_bytes( data ) )
		
		self.a0		/= 2**3
		self.b1		/= 2**13
		self.b2		/= 2**14
		self.c12	/= 2**24

	def _pressure_temp( self ):
		data	= self._insert_zero_bytes( [ 0x80, 0x82, 0x84, 0x86  ] )
		
		self._cs_ctrl( 0 )
		self.spi.write_readinto( data, data )
		self._cs_ctrl( 1 )

		self.data_ready	= False

		p, t	= unpack( ">HH", self._collect_odd_bytes( data ) )
		p	>>= 6
		t	>>= 6
		
		return ( p, t )

	def _collect_odd_bytes( self, data ):
		#	doing similar to data = data[1::2] because MicroPython doesn't support "::2"
		return bytearray( [ x for i, x in enumerate( data ) if i % 2 ] )

	def _insert_zero_bytes( self, data ):
		return bytearray( sum( [ [x, 0x00] for x in data ], [] ) + [ 0x00 ] )

	def _cs_ctrl( self, state ):
		if self.cs:
			self.cs.value( state )
			
	def _set_ready_flag( self, _ ):
		self.in_meas	= False
		self.data_ready = True
		
		
def callback( x ):
	global timer_flag
	timer_flag = True 

def main():
	global timer_flag
	timer_flag	= False
	LOG_FILE	= "mpl3155.csv"
	I2C_FREQ	= 400000
	SPI_FREQ	= 1000000
	SAMPLING	= 10

	if "MIMXRT" in os.uname().machine:
		spi	= SPI( 0, SPI_FREQ, cs = 0 )
		s0	= MPL115A1( spi, None )

		i2c	= I2C( 0, I2C_FREQ )
		s1	= MPL3115A2S( i2c )

		led		= Pin( "D4", Pin.OUT )
		
	elif "Raspberry Pi Pico" in os.uname().machine:
		spi	= SPI( 1, SPI_FREQ, sck = Pin( 10 ), mosi = Pin( 11 ), miso = Pin( 12 ) )
		s0	= MPL115A1( spi, Pin( 13, Pin.OUT ) )

		i2c	= I2C( 0, sda = Pin( 0 ), scl = Pin( 1 ), freq = I2C_FREQ )
		s1	= MPL3115A2S( i2c )

		led		= Pin( "LED", Pin.OUT )
	
	Timer( -1, mode = Timer.PERIODIC, freq = SAMPLING, callback = callback )

	count	= 0

	while True:
		if timer_flag:
			timer_flag	= False
			led.value( 1 )
	
			p0	= s0.pressure()
			p1	= s1.pressure()
	
			dt	= localtime()
			p_str	= "{:04d}-{:02d}-{:02d} {:02d}:{:02d}:{:02d}, {}, {}, {}".format( dt[ 0 ], dt[ 1 ], dt[ 2 ], dt[ 3 ], dt[ 4 ], dt[ 5 ], p0, p1, count )
			print( p_str )

			with open( LOG_FILE, "a" ) as f:
				print( p_str, file = f )

			count	+= 1
			led.value( 0 )

if __name__ == "__main__":
	main()