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I2C examples

Some examples of reading and writing to devics on the tilda-mk6 badge in micropython. Note, some of these examples may leave the chips in a different state to their original and therefore the chips may need to be reset before any other examples are attempted.

Getting started

initialise an i2c object to use:

from machine import I2C
from machine import Pin
i2c = I2C(scl=Pin(41), sda=Pin(42))

scan the i2c bus for devices:

>>> i2c.scan()                                                                   
[18, 44, 80]

There should be three devices show, 18 is the QMA7981 accelerometer, 44 is the QMC7983 magnetic sensor and 80 is the A1006 crpto chip (to be replaced?)

QMA7981

Read the identity byte from register 0x00:

>>> i2c.readfrom_mem(18,0,1)
b'\xe7'

interrupt reading (the values assume the chip has an interrupt asserted, if not the values will be oposite):

>>> from machine import Pin
>>> irq = Pin(40, Pin.IN, Pin.PULL_UP)
>>> irq.value()
0

set interrupt pin to active high:

>>> i2c.writeto_mem(18, 0x20, 4);
>>> irq.value();
5

set interrupt pin back to active low:

>>> i2c.writeto_mem(18, 0x20, b'5')                                              
>>> irq.value()                                                                  
0

to do a power-on reset...

>>> i2c.writeto_mem(18, 0x36, b'\xb6')

read the power-state:

bytes = i2c.readfrom_mem(18, 0x11, 1)
print("{}".format(bytes[0]))

read the data int status:

>>> bytes = i2c.readfrom_mem(18, 0x0b, 1)
>>> print("{}".format(bytes[0]))

initialse settings to 2G, 1024Hz bandwidth

>>> i2c.writeto_mem(18, 0x11, b'\xc0')
>>> i2c.writeto_mem(18, 0xf,  b'\x01')
>>> i2c.writeto_mem(18, 0x10,  b'\x05')

do a simple read of the x/y/z acceleration values:

>>> i2c.writeto_mem(18, 0x11, b'\xc0')
>>> bytes = i2c.readfrom_mem(18, 1, 6)
>>> x = (bytes[0] >> 2) | (bytes[1] << 6)
>>> y = (bytes[2] >> 2) | (bytes[3] << 6)
>>> z = (bytes[4] >> 2) | (bytes[5] << 6)
>>> print("{} {} {}".format(x, y, z))

QMC7983

Read the chip identification register:

>>> i2c.readfrom_mem(44, 0xD, 1)
b'2'

do a basic initialisation, as per the datasheet

>>> i2c.writeto_mem(44, 0xb, b'\x0f')
>>> i2c.writeto_mem(44, 0x9, b'\x3d')

read all the data registers

>>> bytes = i2c.readfrom_mem(44, 0x0, 8)
>>> print("{}".format(bytes))
b'\xd8\x07\x19\n\x8e_\x00\xfe'

References