Connecting nxt ultrasonic sensor with a hitechnic sensor multiplexer does not work

ev3dev version: 4.14.80-ev3dev-2.3.1-ev3

ev3dev-lang-python version: ii python3-ev3dev 1.2.0 all Python language bindings for ev3d ii python3-ev3dev 2.0.0~beta2 all Python language bindings for ev3d

I am trying to connect a lego nxt ultrasonic sensor to my ev3 through an hitechnic sensor multiplexer. I read that i have to manually set the device with “set_device = “lego-nxt-us””. I am always getting an OSError: [Errno 22] Invalid argument error.

My code:

port = LegoPort(address="in2:i2c8:mux2")
port.mode = 'i2c'
port.set_device = "lego-nxt-us"
us = UltrasonicSensor(address="in2:i2c8:mux")

The error:

line 3, in <module>    
    port.set_device = "lego-nxt-us"
 File "/usr/lib/python3/dist-packages/ev3dev/core.py", line 3077, in set_device
    self._set_device = self.set_attr_string(self._set_device, 'set_device', value)
 File "/usr/lib/python3/dist-packages/ev3dev/core.py", line 229, in set_attr_string
    return self._set_attribute(attribute, name, value)
 File "/usr/lib/python3/dist-packages/ev3dev/core.py", line 211, in _set_attribute
    attribute.write(value.encode())
OSError: [Errno 22] Invalid argument

I tried everything and need your help now. Thanks in advance.

[dlech]

This mux itself also show up as a sensor. You can use the generic Sensor class for this. If I recall, you have to put the mux in RUN mode before you can read any values. The DETECT mode can be a bit temperamental, but it should be able to be used to detect the LEGO NXT Ultrasonic sensor. Also, the UltrasonicSensor class is probably just for the EV3 Ultrasonic sensor, not the NXT one, so you probably need to use the generic Sensor class for that too.

• https://python-ev3dev.readthedocs.io/en/ev3dev-stretch/sensors.html#base-sensor
• http://docs.ev3dev.org/projects/lego-linux-drivers/en/ev3dev-jessie/sensor_data.html#ht-nxt-smux
• http://docs.ev3dev.org/projects/lego-linux-drivers/en/ev3dev-jessie/sensor_data.html#lego-nxt-us

[dlech]

Good thinking to check dmesg. -12 means ENOMEM. Looking at the driver code, it looks like we have a serious mistake. We are forgetting to allocate some memory for the sensor modes.

I’ve started https://github.com/ev3dev/ev3dev/issues/1210 to track the issue since this isn’t a python problem. Further comments should be made there.