Hub to Hub code examples

[rbeckett75]

I'm getting started with a new project, and still very new to pybricks coding...

I'm looking at having a train run up and down a track, (thanks @eggybricks for really nice clear code examples!) and then have a loader, and unloader mechanism at each end (each using a hub/motor) - So at least 3 hubs

while working my way through examples, I found this - is it still true?
https://pybricks.com/projects/tutorials/wireless/hub-to-hub/broadcast/#known-issue-broadcasting-using-the-city-hub-does-not-work
or has it been fixed in the beta of pybricks that I'm using?

Ultimately, I would like the train hub, once it has reached a station, to send a simple signal to a hub, eg: "Load", and then that hub to send a signal back "Done", to allow the train to go.

unlike the examples, I don't need to send constant data (motor angles, etc)..

I have managed to get this working in the powered up app, so hopefully it should be easy to replicate in pybricks.

If anyone has any code examples that do a similar task, I'd love to see them!

thanks!
Rohan.

[dlech]

or has it been fixed in the beta of pybricks that I'm using?

Yes, it should be fixed since beta 3.3.0b6. https://github.com/pybricks/pybricks-micropython/blob/master/CHANGELOG.md#fixed-3

[rbeckett75]

I've managed to get the following code working (very rough), and it mostly seems to work.
It definitely works 'smoother' and more consistant, when I detach from the PC, and restart the code on the hub independantly.. so that's good.
But I think I need to work on the timing, as sometimes, it still doesn't transmit, or recieve both commands (currently set 2 seconds apart)
sometimes it only does one!

• Can anyone suggest any cleaner way of doing it?
• Is there a way to stop broadcasting?

by use of the LED light in different sections of the code, I can see that once broadcasting starts, it never seems to stop, and the recieving hub (Unloader) will blink red/green occasionally, indicating it's picking up some broadcast

Code from the "Train" - incomplete - all it does is send a broadcast a command when it detects red
ultimately it will be a loop as the train runs from one end of the track to the other

from pybricks.hubs import CityHub
from pybricks.pupdevices import Motor, Light, ColorDistanceSensor
from pybricks.parameters import Button, Color, Direction, Port, Stop
from pybricks.tools import wait, StopWatch

trainhub = CityHub(broadcast_channel=1, observe_channels=[2,3])
trainmotor = Motor(Port.A)
trainsensor = ColorDistanceSensor(Port.B)

check_color_interval_ms = 20

def check_for_color(color):
    while trainsensor.color() != color:
        wait(check_color_interval_ms)

print("Program Started")

while True:
    print("Waiting for Red")
    trainhub.light.on(Color.RED)
    check_for_color(Color.RED)
    print("Red detected")
    trainhub.light.on(Color.ORANGE)
    print("LED Orange - sending Load Command")
    trainhub.ble.broadcast(1)
    wait(2000)
    print("LED Orange - sending UnLoad Command")
    trainhub.ble.broadcast(2)
    wait(2000)
    print("Stop Broadcasting?")
    trainhub.ble.broadcast(0)

wait(200)  

Code from the Unloader - experimenting with recieving 2 commands, although it will really only need a single command and then a simple back/forth motor movement

from pybricks.hubs import CityHub
from pybricks.pupdevices import Motor, Light
from pybricks.parameters import Button, Color, Direction, Port, Side, Stop
from pybricks.tools import wait, StopWatch

UnloaderHub = CityHub(observe_channels=[1], broadcast_channel=3)
UnloaderMotor = Motor(Port.A)

print("Program Started, Waiting for Command")


while True:
    # Receive broadcast from the other hub.

    data = UnloaderHub.ble.observe(1)

    if data is None:
        UnloaderHub.light.on(Color.RED)
    else:
        UnloaderHub.light.on(Color.GREEN)
        command = data[0]
        if command is 1:
            wait(200)
            print("command 1 recieved")
            UnloaderHub.light.on(Color.ORANGE)
            print("Run Motor forwards")
            UnloaderMotor.dc(70)
            wait(1500)
            print("Stop Motor")
            UnloaderMotor.stop()
            wait(1500)
            data = None
        elif command is 2:
            wait(200)
            print("command 2 recieved")
            UnloaderHub.light.on(Color.ORANGE)
            print("Run Motor backwards")
            UnloaderMotor.dc(-70)
            wait(1500)
            print("Stop Motor")
            UnloaderMotor.stop()
            wait(1500)
            data = None

wait(200)

I am learning a bit.. although it's frustrating when it doesn't seem to work consistantly!
thanks again :)

[dlech]

Due to the way broadcasting works (sending the same data over and over multiple times per second), I think it works best to send a state rather than commands or events. To take your example, instead of the first hub waiting for a color and then sending a series of commands, you could just send the color. Then on the second hub, you could have all of the logic needed in one place and just treat the color from the other hub as if it was an extra local color sensor.

from pybricks.hubs import CityHub
from pybricks.pupdevices import Motor, Light, ColorDistanceSensor
from pybricks.parameters import Button, Color, Direction, Port, Stop
from pybricks.tools import wait, StopWatch

trainhub = CityHub(broadcast_channel=1, observe_channels=[2,3])
trainmotor = Motor(Port.A)
trainsensor = ColorDistanceSensor(Port.B)

print("Program Started")

while True:
    color = trainsensor.color()
    trainhub.ble.broadcast(str(color))
    # broadcasts are sent every 100ms so no reason to update faster
    wait(100)

from pybricks.hubs import CityHub
from pybricks.pupdevices import Motor, Light
from pybricks.parameters import Button, Color, Direction, Port, Side, Stop
from pybricks.tools import wait, StopWatch

UnloaderHub = CityHub(observe_channels=[1], broadcast_channel=3)
UnloaderMotor = Motor(Port.A)


def check_for_color(color):
    while True:
        # Receive broadcast from the other hub.

        data = UnloaderHub.ble.observe(1)

        if data is None:
            UnloaderHub.light.on(Color.RED)
        else:
            UnloaderHub.light.on(Color.GREEN)
            rx_color = data[0]

            if str(color) == rx_color:
                return
            
        wait(100)

print("Program Started")


while True:
    print("Waiting for Red")
    check_for_color(Color.RED)
    print("Red detected")

    UnloaderHub.light.on(Color.ORANGE)
    print("Run Motor forwards")
    UnloaderMotor.dc(70)
    wait(1500)
    print("Stop Motor")
    UnloaderMotor.stop()
    wait(1500)

    print("Run Motor backwards")
    UnloaderMotor.dc(-70)
    wait(1500)
    print("Stop Motor")
    UnloaderMotor.stop()
    wait(1500)

    print("Waiting for not Red")
    check_for_color(Color.NONE)