Duplo train project, how to read the color sensor

[thebrickmg]

Hi
I just started to code with pybricks. I have a bit of an idea how to code, but I get stuck in this Duplo train project.
I do build Lego GBC Modules (Great Ball Contraption) and I already have a module with the Duplo train, The problem is, that the train stops after 15 minutes. I have a video here:
https://youtu.be/VLBbY-jCAsI

So I was very happy, when I found this projekt:
https://pybricks.com/projects/tutorials/wireless/hub-to-hub/pybricks-to-official-fw/

The train should go forward and backward (not in an endless round) to go from loading to unloading. So I still have to check, were is the end of the tracks. And for this reason I need to read the color sonsor in the train. And unfortunatly I have no idea how to do that. I have no problem to use different colors and both ends.
Thank you for any help

[laurensvalk]

@NStrijbosch, did you perhaps have an existing example to read some data from a LWP3 device?

Our example (above) only sends stuff.

[NStrijbosch]

This one worked at some point (reading the color sensor of Mario). With some small changes this should work with the duplo train.

from pybricks.hubs import ThisHub
from pybricks.iodevices import LWP3Device
from pybricks.parameters import Color

MARIO = const(0x43)
PORT_VALUE_MSG = const(0x45)

hub = ThisHub()

# Connect to the Mario
mario = LWP3Device(MARIO)
print("connected")

#subscribe to Mario barcode/color sensor
mario.write(b'\x0a\x00\x41\x01\x00\x01\x00\x00\x00\x01')

while True:
    msg = mario.read()

    kind = msg[2]
    
    if kind != PORT_VALUE_MSG:
        continue

    color = msg[6]
    
    print("color:", color)

    if color == 21:  # Mario is on red
        hub.light.on(Color.RED)
    else:
        hub.light.on(Color.BLUE)

[laurensvalk]

Thanks!

I have been working on cleaning up the LWP3 class lately and sharing more internal code with the Remote class.

Since we also have support for Python-based stuff in the firmware now, it's probably not too far fetched to add dedicated classes for the Duplo train and the Mario variants.

For the Duplo hub, I suppose all we need is:

• DC power out
• front light. Is there an RGB mode? Then we could make it work just like the remote light.
• color sensor input. Is there an RGB mode? Or just color index?
• Choo Choo sound trigger.

[thebrickmg]

well, that sounds great :)
But I can not give an answer to any of the questions...

[laurensvalk]

Yeah, it was perhaps more a note to self for further investigation 😄

The non-technical version of that was: which functionality of the train do we want/need? 😄

[NStrijbosch]

I believe the ront light is similar to the other lights on hubs (city/technic/boost)

The motor is indeed DC power out, but you can also measure the speed

The duplo color sensor has multiple modes:

• Intensity
• Reflectivity
• Color
• RGB

The duplo speaker has two modes:

• Sound (i guess the Choo Choo, and more: BRAKE = 3, STATION_DEPARTURE = 5, WATER_REFILL = 7, HORN = 9, STEAM = 10)
• A tone

[MimiVRC]

I'm new to this so I was curious how likely/difficult it would be to make something like this as blocks? adding sensor blocks for the mario hubs since they do support a lot of sensor features, including being able to get the scanned barcode. I know it can be done in code, but I'm looking for block versions of these features!

[thebrickmg]

Thank you for the fast replys.
I guess I have to go on with trial and error with the values in the code:
`MARIO = const(0x43)

PORT_VALUE_MSG = const(0x45)
`
in the given code there is

DUPLO_TRAIN_ID = 0x20

so the color sensor must be a different value, but probably not 0x43 ?
Is this correct?

[NStrijbosch]

It is the first write that subscribes to the color sensor which is important. I just did a quick test with my duplo train:

from pybricks.hubs import ThisHub
from pybricks.iodevices import LWP3Device
from pybricks.parameters import Color
from pybricks.tools import wait

DUPLO_TRAIN = const(0x20)
PORT_VALUE_MSG = const(0x45)

PORT_COLOR_SENSOR = const(0x12)
MODE_RGB = const(0x03)

hub = ThisHub()

# Connect to the duplo train
train = LWP3Device(DUPLO_TRAIN)
print("connected")

#subscribe to Duplo color sensor
train.write(bytes([0x0a, 0x00, 0x41, PORT_COLOR_SENSOR, MODE_RGB, 0x01, 0x00, 0x00, 0x00, 0x01]))

wait(1000)
while True:
    msg = train.read()

    kind = msg[2]
    port = msg[3]
    
    if kind != PORT_VALUE_MSG and port != PORT_COLOR_SENSOR:
        continue

    red = msg[4]
    green = msg[6]
    blue = msg[8]
    
    print("red: ", red, "green: ", green, "blue: ", blue)

Hopefully this helps.
It would be nice to add this to the Duplo_Train class which you found. But I need to spend some time to figure out how to do this properly without the read blocking everything.

[thebrickmg]

Yeah, that works with the color sensor. Now I have to find out how all will work together (train driving and color sensor reading). Thank you so far!!! Great job!!!

[thebrickmg]

This is not nice, but it works:

train.write(bytes([0x08, 0x00, 0x81, 0x00, 0x01, 0x51, 0x00, speed]))

are there any referenz values for colors like green, yellow, red and blue?
I tried it for yellow with

• red between 180 - 220
• green between 9-30
• blue between 165-180

but the train does not stop every time driving over the yellow brick...