jens
b51e2c222d
- 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
118 lines
2.0 KiB
Python
Executable File
118 lines
2.0 KiB
Python
Executable File
#!/usr/bin/python3
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import time
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import spidev
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from atemperatureSensor import ATemperatureSensor
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class Max31865(ATemperatureSensor):
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def __init__(self):
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super(Max31865, self).__init__('Max31865')
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# Open SPI bus
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self.spi = spidev.SpiDev()
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self.spi.open(0, 0)
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self.spi.max_speed_hz = 50000
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self.spi.mode = 0b01
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self.temp_correction = -0.2
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self.write_reg(0x00, 0xA3)
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time.sleep(0.100)
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self.digits = 0
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def read_reg(self, addr):
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reg = self.spi.xfer([addr, 0xFF])
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return reg[1]
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def write_reg(self, addr, data):
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self.spi.xfer([addr+0x80, data])
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def read_digits(self):
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msb = self.read_reg(0x01)
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lsb = self.read_reg(0x02)
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if (lsb & 0x01 == 0x00):
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self.digits = float(256*msb + lsb)/2
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self.write_reg(0x00, 0xA3)
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return self.digits
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def temperature(self):
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return self.__tempRaw()
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def __tempRaw(self):
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try:
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digits = self.read_digits()
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except:
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return None
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R = Max31865.calc_R(430, digits)
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T = Max31865.vanDusen_temp(R) + self.temp_correction
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# print("R={:.3f} Ohm, T={:.2f} degC".format(R, T))
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return T
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@staticmethod
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def calc_R(Rref, digits):
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k = digits / 8192 / 4
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R = k*Rref
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return R
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@staticmethod
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def vanDusenLut (R0, Tmin, Tmax, dT):
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a = +3.90830e-03
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b = -5.77500e-07
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c = -4.18301e-12
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Rv = []
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Tv = []
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T = Tmin
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while T <= Tmax:
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R = R0*(1 + a*T + b*T**2)
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if T < 0.0:
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R += R0*c*(T - 100)*T**3
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Rv.append(R)
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Tv.append(T)
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T += dT
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return Rv, Tv
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@staticmethod
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def vanDusen_temp(Rmeas):
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RLut, TLut = Max31865.vanDusenLut(100, -150, +500, 1.0)
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# Find candidate
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i = 0
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for R in RLut:
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if R > Rmeas:
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break
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i += 1
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# Linear interpolation
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R0 = RLut[i-1]
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R1 = RLut[i]
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T0 = TLut[i-1]
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T1 = TLut[i]
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dR = R1 - R0
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dT = T1 - T0
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k = (Rmeas-R0)/dR
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T = T0 + dT*k
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return T
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# Main
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if __name__ == '__main__':
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max31865 = Max31865()
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for i in range (0, 8):
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print("Reg[0x{}]: 0x{:02X}".format(i, max31865.read_reg(i)))
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max31865.temperature()
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print("End of program")
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