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September 27, 2020 11:59
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| import ustruct | |
| class MAX31855: | |
| """ | |
| Driver for the MAX31855 thermocouple amplifier. | |
| MicroPython example:: | |
| import max31855 | |
| from machine import SPI, Pin | |
| spi = SPI(1, baudrate=1000000) | |
| cs = Pin(15, Pin.OUT) | |
| s = max31855.MAX31855(spi, cs) | |
| print(s.read()) | |
| """ | |
| def __init__(self, spi, cs): | |
| self.spi = spi | |
| self.cs = cs | |
| self.data = bytearray(4) | |
| def read(self, internal=False, raw=False): | |
| """ | |
| Read the measured temperature. | |
| If ``internal`` is ``True``, return a tuple with the measured | |
| temperature first and the internal reference temperature second. | |
| If ``raw`` is ``True``, return the values as 14- and 12- bit integers, | |
| otherwise convert them to Celsuius degrees and return as floating point | |
| numbers. | |
| """ | |
| self.cs.low() | |
| try: | |
| self.spi.readinto(self.data) | |
| finally: | |
| self.cs.high() | |
| # The data has this format: | |
| # 00 --> OC fault | |
| # 01 --> SCG fault | |
| # 02 --> SCV fault | |
| # 03 --> reserved | |
| # 04 -. --> LSB | |
| # 05 | | |
| # 06 | | |
| # 07 | | |
| # > reference | |
| # 08 | | |
| # 09 | | |
| # 10 | | |
| # 11 | | |
| # 12 | | |
| # 13 | | |
| # 14 | --> MSB | |
| # 15 -' --> sign | |
| # | |
| # 16 --> fault | |
| # 17 --> reserved | |
| # 18 -. --> LSB | |
| # 19 | | |
| # 20 | | |
| # 21 | | |
| # 22 | | |
| # 23 | | |
| # > temp | |
| # 24 | | |
| # 25 | | |
| # 26 | | |
| # 27 | | |
| # 28 | | |
| # 29 | | |
| # 30 | --> MSB | |
| # 31 -' --> sign | |
| if self.data[3] & 0x01: | |
| raise RuntimeError("thermocouple not connected") | |
| if self.data[3] & 0x02: | |
| raise RuntimeError("short circuit to ground") | |
| if self.data[3] & 0x04: | |
| raise RuntimeError("short circuit to power") | |
| if self.data[1] & 0x01: | |
| raise RuntimeError("faulty reading") | |
| temp, refer = ustruct.unpack('>hh', self.data) | |
| refer >>= 4 | |
| temp >>= 2 | |
| if raw: | |
| if internal: | |
| return temp, refer | |
| return temp | |
| if internal: | |
| return temp / 4, refer * 0.0625 | |
| return temp / 4 |
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