[Max31865]

- reduce SPI speed to 50 kHz
- in case of fault, return lastt known temp value



git-svn-id: http://moon:8086/svn/projects/HendiControl@289 fda53097-d464-4ada-af97-ba876c37ca34

Control/brewpi/max31865.py

@@ -1,5 +1,6 @@
 #!/usr/bin/python3
 
+import time
 import spidev
 from atemperatureSensor import ATemperatureSensor
 
@@ -11,11 +12,13 @@ class Max31865(ATemperatureSensor):
 		# Open SPI bus
 		self.spi = spidev.SpiDev()
 		self.spi.open(0, 0)
-		self.spi.max_speed_hz = 100000
+		self.spi.max_speed_hz = 50000
 		self.spi.mode = 0b01
-		self.write_reg(0x00, 0xA3)
 		self.temp_correction = -0.2
-
+		self.write_reg(0x00, 0xA3)
+		time.sleep(0.100)
+		self.digits = 0
+		
 	def read_reg(self, addr):
 		reg = self.spi.xfer([addr, 0xFF])
 
@@ -27,16 +30,20 @@ class Max31865(ATemperatureSensor):
 	def read_digits(self):
 		msb = self.read_reg(0x01)
 		lsb = self.read_reg(0x02)
-		self.write_reg(0x00, 0xA3)
-		digits = float(256*msb + lsb)/2
+		if (lsb & 0x01 == 0x00):
+			self.digits = float(256*msb + lsb)/2
 
-		return digits
+		self.write_reg(0x00, 0xA3)
+		return self.digits
 
 	def temperature(self):
 		return self.__tempRaw()
 
 	def __tempRaw(self):
-		digits = self.read_digits()
+		try:
+			digits = self.read_digits()
+		except: 
+			return None
 		R = Max31865.calc_R(430, digits)
 		T = Max31865.vanDusen_temp(R) + self.temp_correction
 #		print("R={:.3f} Ohm, T={:.2f} degC".format(R, T))
@@ -99,6 +106,7 @@ class Max31865(ATemperatureSensor):
 # Main
 if __name__ == '__main__':
 
+
 	max31865 = Max31865()
 	for i in range (0, 8):
 		print("Reg[0x{}]: 0x{:02X}".format(i, max31865.read_reg(i)))