From 6ee2144f00514c510d79ba8f7f6b0c22757614b9 Mon Sep 17 00:00:00 2001
From: Andreas Gattringer <andreas.gattringer@univie.ac.at>
Date: Wed, 6 Dec 2023 08:51:39 +0100
Subject: [PATCH] added SHT45 support
---
.../microcontroller/sensors/sht45/__init__.py | 94 +++++++++++++++++++
1 file changed, 94 insertions(+)
create mode 100644 umnp/microcontroller/sensors/sht45/__init__.py
diff --git a/umnp/microcontroller/sensors/sht45/__init__.py b/umnp/microcontroller/sensors/sht45/__init__.py
new file mode 100644
index 0000000..83401c0
--- /dev/null
+++ b/umnp/microcontroller/sensors/sht45/__init__.py
@@ -0,0 +1,94 @@
+try:
+ from machine import I2C
+except ImportError:
+ from umnp.microcontroller.umock.machine import I2C
+
+import asyncio
+import time
+
+SHT45_HIRES = 0xFD
+NO_HOLD_WAIT_TIME = 18.5 / 1000 / 1000
+SHT45_WAIT_TIME_MS = 9
+SHT45_RESET_TIME_MS = 1
+SHT45_SOFT_RESET = 0x94
+SHT45_DEFAULT_ADDRESS = 0x44
+
+
+class SHT45:
+ def __init__(self, i2c: I2C, i2c_address=SHT45_DEFAULT_ADDRESS):
+ self._i2c = i2c
+ self._i2c_address = i2c_address
+ self._initialised = False
+ self._nan = float("NAN")
+
+ devices = self._i2c.scan()
+
+ if self._i2c_address not in devices:
+ raise RuntimeError("SHT45: Device not found")
+
+ if self.reset():
+ self._initialised = True
+ else:
+ print("Could not initialise device")
+
+ @property
+ def initialised(self) -> bool:
+ return self._initialised
+
+ def _command(self, command: int) -> int:
+ pass
+
+ def _calulate_crc8(self, data, polynom=0x31, init=0xFF):
+ # CRC-8-Dallas/Maxim for I2C with 0x31 polynomial
+ crc = init
+ for byte in data:
+ crc ^= byte
+ for _ in range(8):
+ if crc & 0x80:
+ crc = (crc << 1) ^ polynom
+ else:
+ crc = crc << 1
+ crc &= 0xFF
+ return crc
+
+ def reset(self) -> bool:
+ cmd = bytearray(1)
+ cmd[0] = SHT45_SOFT_RESET
+ n_ack = self._i2c.writeto(self._i2c_address, cmd)
+ time.sleep(SHT45_RESET_TIME_MS / 1000)
+ if n_ack == 1:
+ return True
+ return False
+
+ def _decode_and_verify_value(self, buffer):
+ if self._calulate_crc8(buffer[:2]) != buffer[2]:
+ return self._nan
+
+ return buffer[1] + (buffer[0] << 8)
+
+ def _translate_temperature(self, buffer) -> float:
+ t_raw = self._decode_and_verify_value(buffer)
+ return -45 + 175 * t_raw / (2**16 - 1)
+
+ def _translate_rh(self, buffer):
+ rh_raw = self._decode_and_verify_value(buffer)
+ return -6 + 125 * rh_raw / (2**16 - 1)
+
+ async def measure(self):
+ temperature = self._nan
+ rh = self._nan
+ if not self.initialised:
+ return temperature, rh
+
+ cmd = bytearray(1)
+ cmd[0] = SHT45_HIRES
+ n_ack = self._i2c.writeto(self._i2c_address, cmd)
+ if n_ack != 1:
+ return temperature, rh
+ await asyncio.sleep(SHT45_WAIT_TIME_MS / 1000)
+
+ data = self._i2c.readfrom(self._i2c_address, 6)
+ temperature = self._translate_temperature(data[0:3])
+ rh = self._translate_rh(data[3:6])
+
+ return temperature, rh
--
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