ev3dev using multiple sensors with python

[jamesc601]

Hi.

I am completely new to ev3dev and I am currently looking in to a potential project. This may be done with either lego mindstorm or a raspberry pi. I plan on using multiple ultrasonic sensors in this project. However, I can not seem to find a way to check what a specific sensor senses as all example code I have found seems to only use one sensor and does not identify it by it's port but just as a sensor. Is there a way to do this?

Thanks in advance

[dlech]

You can use the address attribute to figure out what port a sensor is connected to.

[WasabiFan]

Assuming that you are using the library from https://github.com/rhempel/ev3dev-lang-python/ (which is the only up-to-date one as far as I know), something like this should work:

m = ev3.LargeMotor('outA')
m.run_timed(time_sp=3000, duty_cycle_sp=75)

You can find other examples of usage in the readme, and their docs should include info on the constructor parameters you need.

[WasabiFan]

That example code is for a motor, but sensors should work similarly too; the sensor ports are called inA, inB, etc.

[ec-m]

Actually, the sensor ports are called in2, in3 etc. With this you can use multiple ultrasonic sensors in the following way:

us_1 = UltrasonicSensor('in3')
us_2 = UltrasonicSensor('in4')
assert us_1.connected, "Connect a single US sensor to any sensor port"
assert us_2.connected, "Connect a single US sensor to any sensor port"
us_1.mode='US-DIST-CM'
us_2.mode='US-DIST-CM'
units = us_1.units

distance_1 = us_1.value() / 10 # convert mm to cm
print(str(distance_1) + " " + units)
distance_2 = us_2.value() / 10
print(str(distance_2) + " " + units)

[ddemidov]

In stretch the port names have been changed to ev3-ports:in<n>, ev3-ports:out<c>. So it is best to use the predefined constants INPUT_<n>, OUTPUT_<c>.

[ec-m]

@ddemidov Thank you for this information. Then the correct way would be

us_1 = UltrasonicSensor(INPUT_3)
us_2 = UltrasonicSensor(INPUT_4)