If you have any questions, please contact fischertechnik-technik@fischer.de

RX Controller - I2C

The fischertechnik RX controller has 2 connections labeled EXT1 and EXT2 (see 4 in the picture). Both connections are connected to the internal I2C bus, see RX Controller Operating Instructions.

RX Controller	6-pin Assigment

Warning

• Power supply for I2C is 3.3V

Python Code

RX controller uses CircuitPython which is based on Python. However, some commands differ considerably from Python. The basic functions for I2C are listed here.

Important

• To ensure that no other function uses the I2C bus, use i2c.trylock() and i2c.unlock()
• Use i2c.deinit() to turn off the I2C bus
• If you use the with statement (context manager), it automatically locks and unlocks the I2C interface

I2C Imports

import board
import busio
from adafruit_bus_device.i2c_device import I2CDevice
from fischertechnik.logging import log as print

I2C Scan

async def i2cScan():
    i2c = busio.I2C(board.SCL1, board.SDA1, frequency=400000)
    while not i2c.try_lock():
        pass
    try:
      #print("I2C addresses found:", [hex(device_address) for device_address in i2c.scan()],)
      i2cList = i2c.scan()
    finally:  # unlock the i2c bus
      i2c.unlock()
    i2c.deinit()
    return i2cList

I2C Write Buffer

async def i2cWriteBuffer(i2cAdr, write_buffer):
    with busio.I2C(board.SCL1, board.SDA1, frequency=400000) as i2c:
      with I2CDevice(i2c, i2cAdr) as device:
        device.write(bytes(write_buffer))

I2C Read Buffer

async def i2cReadBuffer(i2cAdr, read_length):
    read_buffer = bytearray(read_length)
    with busio.I2C(board.SCL1, board.SDA1, frequency=400000) as i2c:
      with I2CDevice(i2c, i2cAdr) as device:
        device.readinto(read_buffer)
    return read_buffer

I2C Write Read Buffer

async def i2cWriteReadBuffer(i2cAdr, write_buffer, read_length):
    read_buffer = bytearray(read_length)
    with busio.I2C(board.SCL1, board.SDA1, frequency=400000) as i2c:
      with I2CDevice(i2c, i2cAdr) as device:
        device.write_then_readinto(bytes(write_buffer), read_buffer)
    return read_buffer

Examples External I2C Modules

Some examples of external I2c modules already exist. These examples can be imported with the ROBO Pro Coding app.

sensor chip	ROBO Pro Coding program name
	test_RX_i2c_device_scan
	test_RX_i2c_device_template
APDS9960	test_RX_i2c_device_apds9960

Further examples of I2C modules can be found in a ROBO Pro Coding project called ft_Controller_I2C. The documentation (German) was created by the user elssner. Many thanks for the very detailed examples!

Using I2C with Blockly and Python

RX firmware 0.23.1

Please note that with the RX firmware 0.23.1 it is not possible to access from Blockly and Python at the same time, as the I2C instance cannot be used simultaneously.

If the following error occurs, the RX controller must be switched off and on again.

Traceback (most recent call last):
  File "asyncio/core.py", line 246, in run_until_complete
  File "user/mainCode.py", line 100, in run
ValueError: SCL1 in use

RX firmware 0.27.0

In RX firmware 0.27.0 it is now possible to access from Blockly and Python at the same time. Use the following function to get the I2CDevice:

global i2c
import fischertechnik.factories as rx_factory
if rx_factory.i2c_factory is None:
  rx_factory.init_i2c_factory()
i2c = rx_factory.i2c_factory.get_i2c_bus(instance)._i2c

fischertechnik I2C Sensors

Some I2C addresses are already reserved, see e.g. here or www.i2c-bus.org. All fischertechnik I2C sensors are listed in the table below.

Sensor	Item Number	I2C Address	sensor chip	RX Controller	TXT 4.0 Controller	TXT Controller
Environmental sensor 6-pin	182974	0x76	BME680	Yes	Yes
Environmental sensor 10-pin	167358	0x76	BME680	Yes, I2C-Adapter 186150	Yes, I2C-Adapter 186150	Yes (C/C++)
RGB gesture sensor 6-pin	183267	0x39	APDS9960	Yes	Yes
RGB gesture sensor 10-pin	186705	0x39	APDS9960	Yes, I2C-Adapter 186150	Yes, I2C-Adapter 186150	Yes
Kombisensor 6-pin	201257	0x68	ICM42670 (GYRO + ACC)	Yes (FW>=0.26.2)	Yes
		0x30	MMC5603 (MAG)	...	...
Kombisensor 10-pin	158402	0x10	BMX055 (MAG)	Yes, I2C-Adapter 186150	Yes
		0x18	BMX055 (ACC)	...	...
		0x68	BMX055 (GYRO)	...	...
RGB color sensor	213965	0x14	Knobloch		Yes (txtapi>=6.4.0)
NFC module	-	0x24	PN532 NFC RFID Module		Yes	Yes (C/C++)
AGV charging module	-	0x26	Knobloch		Yes
RESERVED		0x8		RESERVED

Connector I2C - 10-pin (TXT Controller, Deprecated)

Warning

• Power supply for I2C is 3.3V
• No separate power supply at the plug