[Bug] Sensor's only works once. Hub needs restart to make them work again

[Vinz1911]

Describe the bug
I tried the following on the Inventor Hub with the ColorSensor and the UltraSonic Sensor:
Version: ('primehub', '3.1.0a3', 'v3.1.0a3-62-g51bdd097 on 2021-08-26')

Problem: Sensor's only works on first run of the script after stopping the script and run it again, the sensor's are not working.
After restart of the hub, the sensor's work again for the first run and then the problem appears again.

To reproduce
Steps to reproduce the behavior:
Just run this script, stop it and run it again:

from pybricks.pupdevices import ColorSensor, UltrasonicSensor
from pybricks.parameters import Port
from pybricks.tools import wait
from pybricks import version

# Initialize the sensor.
sensor = UltrasonicSensor(Port.C)
sensor.lights.on(100)

while True:
    distance = sensor.distance()
    print(distance)
    wait(100)

Expected behavior
Sensor's work every time the script is running

[BertLindeman]

@Vinz1911 I tried this on my cityhub (as it was next to me) with an UltraSonic sensor:
What I noticed:
First run after hub boot and BT connect running as expected.
Stop run and start the program again:

• Sensor light does not go ON
• measured distance is constant 2000

After disconnect and re-boot the hub:
the first run is OK.

{edit typo]

[Vinz1911]

Hi @BertLindeman

Exactly, thats also the behaviour i discovered. With the Color Sensor it shows constantly Color.NONE

[BertLindeman]

@Vinz1911 I used ambient on the color sensor and THAT keep working the second run.
My current program:

print(version)
from pybricks.pupdevices import ColorSensor, UltrasonicSensor
from pybricks.parameters import Port
from pybricks.tools import wait
from pybricks import version

# Initialize the sensor.
sensorA = UltrasonicSensor(Port.A)
sensorA.lights.on(60)
sensorB = ColorSensor(Port.B)
sensorB.lights.on(60)
i = 0
while True:
    # distance = sensor.distance()
    # print(distance)
    i += 1
    sensorA.lights.on(i)
    sensorB.lights.on(60)
    print(i, sensorA.distance(), sensorB.ambient())
    wait(500)

Part of the second run:

('cityhub', '3.1.0a3', 'v3.1.0a3-60-ga2b2e44e on 2021-08-18')
1 2000 0.2
2 2000 0.2
3 2000 0.2
4 2000 0.1
5 2000 0.0

[edit: forgot to paste the program]

[Vinz1911]

Just as Info:

I discovered that you don't need to use the sensor's in Code. You can also run the default main script delivered with the Firmware. Press Start, then Stop will disable the Sensor (Light's Go off) and then they stay off.

[laurensvalk]

Thanks for opening this issue. This used to be fixed, but it sounds like it has come back.

If you want to help, it would be great to know when this started happening by going through older builds.

Which was the last build that worked? It's usually best to make big jumps first (like going back a couple of weeks), and then make smaller steps as you get closer.

I discovered that you don't need to use the sensor's in Code. You can also run the default main script delivered with the Firmware. Press Start, theb Stop will disable the Sensor (Light's Go off) and then they stay off.

This is good, because it's relatively quick to see whether it was still working for a particular version.

The probably happens because we turn off power to all ports at the end of a program. There is a check to skip this for LEGO sensors with particular properties, but apparently this is no longer being checked.

[Vinz1911]

Hi Laurens,

Yes sure, i will test it later today and give you feedback here 😊