Creating multiple things in a loop

Novski · November 8, 2019, 7:54am

I’m implementing 8x ds18b20 temperature sensors as webthing. The protocol that they use is 1wire. Now i have a running loop collecting id’s and temperature of those eight sensors and i wold like to create a webthing for each. I looked in to the multiple thing example but don’t see how to create multiple things in a loop.
Is that actually possible?

mstegeman · November 8, 2019, 5:10pm

The webthing libraries do not handle adding/removing things at runtime well. They expect the complete list of things to be present when the server is started.

Novski · November 8, 2019, 5:54pm

Does that mean that I can loop through my sensors and create as many as are found on the 1wire line and then start the server with a list of things like:

list_of_things = [sensor1, sensor 2, sensor 3]
server = WebThingServer(MultipleThings(list_of_things, 'some devices'), port=8888)

or do you mean exactly that, is not handled properly?

mstegeman · November 8, 2019, 5:58pm

Yes, that would be the right thing to do. My point was just that you’ll have to stop looping after you start the server, because it’s not straightforward to add new devices after that point.

Novski · November 14, 2019, 8:15am

Do people here do code reviews?
I made the w1 bus sensor to be read in loop and added to a list that is initialized by Multiplethings.
Did I do everything right? https://pastebin.com/7Tc1FvFm

mstegeman · November 14, 2019, 4:47pm

At first glance, this looks reasonable. Are you having issues, or just wanting another set of eyes?

Novski · November 14, 2019, 5:03pm

just another set of eyes.
It seams to work perfect, but im not in any way a experienced Programmer. Like to know what can be done better all the times…

Novski · November 19, 2019, 8:33pm

I discovered issues over time.
I Don‘t yet understand when it ocours.
Is it a good practice to read from the sensor every 30s the temperature and updateValue() ?
Or should the gateway request a read from the sensor?
And if, how does a Log view (chart) request values?

Do i maybe have a race condition here with the gateway trying to get values while the webthing is reading in a loop and pushing to to the gateway every few seconds?

mstegeman · November 19, 2019, 9:08pm

The gateway opens a WebSocket connection to your thing and just listens for property updates. It only polls when a WebSocket is not available, like with webthing-arduino.

Generally speaking, it should be fine for your code to read from the sensor whenever it wants. What’s the actual problem you’re having?

Here’s an example of reading from a (fake) sensor every 3 seconds: https://github.com/mozilla-iot/webthing-python/blob/master/example/multiple-things.py#L132-L144

Novski · November 27, 2019, 7:42pm

my setup has a separate webserver, maybe that makes my sensors disapear after some time…

Is it possible to have a openwrt Luci webconfig on port 80 as well as the webthing on port 8888?

started like this:

server = WebThingServer(MultipleThings(things_list, TemperatureDevice'), 
                        port=8888)

Novski · December 1, 2019, 7:49pm

I had the call to the sensors aside of run_server() that made my sensor work for (i asume) only one read_one(). Then they turn not responding.
patched that and uploaded it to git: https://github.com/novski/w1_webthing

I also moved the luci panel to Port 8080 but still i do not get RESTfull api when opening my http://myurl.local or http://myurl.local:8888

and should I not see the json in the console?

Novski · March 13, 2020, 4:48pm

I managed to get the json view if i visit http://myurl.local:8888 but my things do not resolve to:
http://myurl.local:8888/things/first-thing
instead its:
http://myurl.local:8888/first-thing
why does that happen?

github.com

novski/w1_webthing/blob/master/multiple_w1_things.py

#!/usr/bin/python
# coding=utf-8
from __future__ import division, print_function
from webthing import (Action, Event, MultipleThings, Property, Thing, Value,
                      WebThingServer)
import logging
import random
import time
import tornado.ioloop
import uuid
import os, sys

device_id_list = []
things_list = []

class TemperatureSensors(Thing):
    """A Temperature sensor which updates its measurement every few seconds."""

    def __init__(self, device, number):
        self.device = str(device)

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mstegeman · March 13, 2020, 5:22pm

The URL paths are not required to match any specific pattern, just like websites are not forced to conform to some predefined set of URLs.

Novski · March 13, 2020, 5:38pm

Ah, strange. The definition let me assume it has to be /things as all the examples are with it. https://iot.mozilla.org/wot/#thing-resource
Thanks for the clarification.