BME280 on a Pi Zero 2 W with smbus2

# A BME280 on a Raspberry Pi Zero 2 W, over smbus2.
# SDA to GPIO2 (pin 3), SCL to GPIO3 (pin 5), VIN to 3V3 (pin 1), GND (pin 9).
# bme280_smbus.py reads it with the datasheet's compensation formulas.
import time
from smbus2 import SMBus
from bme280_smbus import BME280

bus = SMBus(1)
print("chip id 0x%02x" % bus.read_byte_data(0x76, 0xD0))   # 0x60 is a BME280
sensor = BME280(bus, 0x76)

while True:
    t, p, h = sensor.read()
    print("%.2f C  %.2f hPa  %.1f %%RH" % (t, p, h))
    time.sleep(2)

# bme280_smbus.py: read a Bosch BME280 from a Raspberry Pi over smbus2 on
# /dev/i2c-1, with the compensation formulas of the BME280 datasheet
# (BST-BME280-DS002, section 8.1, the double-precision ones). Runs unchanged
# on a real Pi with "pip install smbus2".

import time
from smbus2 import SMBus


def _s16(lo, hi):
    v = lo | hi << 8
    return v - 65536 if v > 32767 else v


class BME280:
    def __init__(self, bus=1, address=0x76):
        self.i2c = SMBus(bus) if isinstance(bus, int) else bus
        self.address = address
        chip = self.i2c.read_byte_data(address, 0xD0)
        if chip != 0x60:
            raise RuntimeError('no BME280 at 0x%02x (chip id 0x%02x)' % (address, chip))
        c = self.i2c.read_i2c_block_data(address, 0x88, 26)
        h = self.i2c.read_i2c_block_data(address, 0xE1, 7)
        self.t1 = c[0] | c[1] << 8
        self.t2 = _s16(c[2], c[3])
        self.t3 = _s16(c[4], c[5])
        self.p1 = c[6] | c[7] << 8
        self.p = [_s16(c[i], c[i + 1]) for i in range(8, 24, 2)]
        self.h1 = c[25]
        self.h2 = _s16(h[0], h[1])
        self.h3 = h[2]
        e4, e5, e6 = h[3] - 256 if h[3] > 127 else h[3], h[4], h[5] - 256 if h[5] > 127 else h[5]
        self.h4 = e4 * 16 | (e5 & 0x0F)
        self.h5 = e6 * 16 | (e5 >> 4)
        self.h6 = h[6] - 256 if h[6] > 127 else h[6]

    def read(self):
        """One forced measurement: (degrees C, hPa, % relative humidity)."""
        a = self.address
        self.i2c.write_byte_data(a, 0xF2, 0x01)        # humidity x1
        self.i2c.write_byte_data(a, 0xF4, 0x25)        # temperature x1, pressure x1, forced
        time.sleep(0.01)
        while self.i2c.read_byte_data(a, 0xF3) & 0x08:
            time.sleep(0.002)
        d = self.i2c.read_i2c_block_data(a, 0xF7, 8)
        adc_p = d[0] << 12 | d[1] << 4 | d[2] >> 4
        adc_t = d[3] << 12 | d[4] << 4 | d[5] >> 4
        adc_h = d[6] << 8 | d[7]

        v1 = (adc_t / 16384.0 - self.t1 / 1024.0) * self.t2
        v2 = (adc_t / 131072.0 - self.t1 / 8192.0) ** 2 * self.t3
        t_fine = v1 + v2
        celsius = t_fine / 5120.0

        p2, p3, p4, p5, p6, p7, p8, p9 = self.p
        v1 = t_fine / 2.0 - 64000.0
        v2 = v1 * v1 * p6 / 32768.0 + v1 * p5 * 2.0
        v2 = v2 / 4.0 + p4 * 65536.0
        v1 = (p3 * v1 * v1 / 524288.0 + p2 * v1) / 524288.0
        v1 = (1.0 + v1 / 32768.0) * self.p1
        pascals = 0.0
        if v1:
            pascals = 1048576.0 - adc_p
            pascals = (pascals - v2 / 4096.0) * 6250.0 / v1
            v1 = p9 * pascals * pascals / 2147483648.0
            v2 = pascals * p8 / 32768.0
            pascals += (v1 + v2 + p7) / 16.0

        hum = t_fine - 76800.0
        hum = (adc_h - (self.h4 * 64.0 + self.h5 / 16384.0 * hum)) * (
            self.h2 / 65536.0 * (1.0 + self.h6 / 67108864.0 * hum * (1.0 + self.h3 / 67108864.0 * hum)))
        hum = hum * (1.0 - self.h1 * hum / 524288.0)
        hum = min(max(hum, 0.0), 100.0)
        return celsius, pascals / 100.0, hum