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SMBus compatible class

Usage

This is a smbus compatibility class. You can use it to run any I2C Python library for Raspberry Pi or micropython just using MCP2221's I2C device interface.

Usage:

from EasyMCP2221 import SMBus

bus = SMBus()

or

from EasyMCP2221 import smbus

bus = smbus.SMBus()

Note

To use other mcp functions in addition to SMBus, do not create a new MCP Device. It will interfere with existing bus resulting in unpredictable behavior. Always re-use bus.mcp object (see example 2).

Example 1: Basic weather station

In this example, we are using a library from Pimoroni/BME280 to read Temperature, Barometric Pressure and Relative Humidity from a BME280 sensor.

That library is designed for Raspberry Pi or any other system that supports SMBus protocol. It works together with EasyMCP2221 via SMBus class.

Install:

pip install pimoroni-bme280 EasyMCP2221

Example code:

import time
from EasyMCP2221 import SMBus
from bme280 import BME280

bus = SMBus(1)
bme280 = BME280(i2c_dev=bus)

while True:
    temperature = bme280.get_temperature()
    pressure = bme280.get_pressure()
    humidity = bme280.get_humidity()
    print('{:05.2f}*C {:05.2f}hPa {:05.2f}%'.format(temperature, pressure, humidity))
    time.sleep(1)

Output:

17.93*C 933.76hPa 51.57%
17.92*C 933.76hPa 51.57%
17.91*C 933.77hPa 51.53%
17.91*C 933.77hPa 51.50%
17.91*C 933.77hPa 51.54%
...

Example 2: Real Time Clock with LCD

This is a digital clock with two I2C chips:

  • DS1307 as RTC
  • LCD display based on with PCF8574 I2C adapter.

It also shows how to re-use mcp object to further configure MCP2221.

Main loop:

  • DS1307 is configured as 1Hz square oscillator.
  • MCP2221's GP2 is configured as Interrupt on Change.
  • The rising edge of DS1307's output triggers the update cycle.

Full code on EasyMCP2221 examples/clock

from EasyMCP2221 import SMBus
from lcd_driver import LCD
from DS1307 import DS1307

# Create SMBus and instances
bus = SMBus()
lcd = LCD(bus, addr=0x3F)
ds = DS1307(bus, addr=0x68)

bus.mcp.I2C_speed(100_000) # DS1307 only supports 100kHz

bus.mcp.set_pin_function(
    gp0 = "GPIO_IN",  # unused
    gp1 = "IOC",      # trigger update LCD each second
    gp2 = "DAC",      # simulate backup battery
    gp3 = "LED_I2C")  # i2c traffic indicator

bus.mcp.DAC_write(21) # about 3.28V with 5V Vcc
bus.mcp.IOC_config(edge = "rising")

# Initialization after a complete power loss
if ds.halted():
    ds.write_now()
    ds._write(0x07, 0b0001_0000) # sqwe 1Hz
    print("RTC initialized with current timestamp")
else:
    print("RTC was already initialized")

lcd.clear()

# Update only when GP1 changes using Interrupt On Change
while True:
    if bus.mcp.IOC_read():
        bus.mcp.IOC_clear()
        (year, month, day, dow, hours, minutes, seconds) = ds.read_all()

        lcd.display_string("%02d/%02d/20%02d" % (day, month, year), 1)
        lcd.display_string("%02d:%02d:%02d" % (hours, minutes, seconds), 2)

Full reference

Based on kplindegaard/smbus2 interface.

See The SMBus Protocol for more information.

EasyMCP2221

SMBus