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Thread: Mesh network of wireless thermometers/sensors

  1. #1
    Not really a Hairy Aussie
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    Lightbulb Mesh network of wireless thermometers/sensors

    So I had the bright idea to setup a mesh network of wireless thermometers in my house using Arduinos (or clones) and RFM69 915MHz wireless transceivers mainly with the intent of datalogging the temperature of the various rooms over time. My primary interest driving this project is to see if I can dial in the HVAC system to keep the temperature more consistent room to room by controlling the airflow to the different vents in the rooms with the manual dampers installed in the system. In order to do that I need good simultaneous temperature data for the various areas of the house.

    LowPowerLab has a hardware and software project to make a base gateway that uses a RPi + Arduino (or clone) to be the web interface + logging component. They also have a number of low power Arduino clones called Moteino. Their M0 version can connect the wireless transceiver and their Temp+Humidity+pressure board directly to the back without harnesses or adapters.

    To start I only bought the MightyHat kit to use with an RPi3 I already have and one M0 node + sensor to make sure it will really do what I want. If that proves successful I will scale things up. For most of the remote nodes I don't need atmospheric pressure or humidity, so I plan to make them less expensively by using an Anarduino Mini-Wireless boards with the appropriate radio option & a DS18B20 temp sensor. However, a few nodes will have the nicer BME280 sensor so I can monitor the humidity in the garage, basement, and each floor of the house. I don't plan to run from batteries so the slightly cruder hardware design of the Anarduino board that's less suited for battery operation won't be a limiting factor for me.

    I'm basically thinking to stick the "ino" board to a wall wart powering it and then plug them in outlets around the house where I want to monitor the temperature. I will make sure the temperature sensor isn't warmed by the wall wart or directly getting blown on by the HVAC registers. Everything basically looks pretty much plug and play and already has the SW developed for this so I won't have to spend a lot of time on the software side trying to make it all work. *fingers crossed*

  2. #2
    Fixture ddrueding's Avatar
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    I've been looking for a good PoE (802.3af) Arduino for similar things. I prefer wired, and not having individual bricks to stuff. Other than that I would also be interested in your progress.
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  3. #3
    Not really a Hairy Aussie
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    I would expect that running a TCP/IP stack is beyond the scope of Arduino class hardware. There's a somewhat similar RPi Zero W solution I was first looking at. My first inclination was to find a wired Ethernet solution, but I didn't turn up anything I felt was practical to have a bunch of. The solution I'm looking at could be done from batteries without wall warts The Moteino board are very low power, but I don't see battery power as a benefit for me. I might end up with one or two sensors nodes that are battery powered, but I'm unsure of that for now.

    Frankly, I don't think there's a good battery solution. The boards want regulated 3.3V or >3.6V so they can make 3.3V with their linear regulator. So, that leaves you with what 4AA's? 3AA's will fall below the minimum regulation voltage before they're dead. LiIon has the same problem. You could use a small boost circuit to allow 1AA or 2AA to make 3.3V, but that's more complexity and less plug and play. If I was mass producing these and making custom PCBs that would be more viable.

    On your PoE idea, there's this, but it seems somewhat impractical to me. It also doesn't really end up being a clean compact solution. Plus the RPi3 is way overkill for taking temperature readings. I have a lot of CAT6 ports in my house, but I have far more 120V outlets. Sticking the compact hardware to the wall wart takes care of mounting too. I'd trim the power cord to be only long enough to reach the "ino" board and I wouldn't have to find a place to hang or set the board or have cords running to it. Hopefully the wall wart's close proximity doesn't interfere with the wireless transceiver.

  4. #4
    Fixture ddrueding's Avatar
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    I have several Arduino Yun Rev 2 boards coming for a different project, should be here Monday. Could do a poe breakout, but don't need it for this application.

  5. #5
    Not really a Hairy Aussie
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    $59 each...

    And the Wifi and Ethernet is handled by the 400MHz Atheros AR9331 WiFi SoC, 64MB of DDR2 RAM, and 16MB of flash. Not exactly a low power embedded micro.
    Last edited by Stereodude; 10-21-2018 at 06:07 PM.

  6. #6
    Fixture ddrueding's Avatar
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    ...and still no PoE. If there was something appropriate I'd be there by now.
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  7. #7
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    Quote Originally Posted by Stereodude View Post
    I would expect that running a TCP/IP stack is beyond the scope of Arduino class hardware.
    Apparently I was quite wrong. NodeMcu products using the ESP8266 are sub $10 and have a TCP/IP stack.

    On my mesh network of sensors project I soldered up my hat for the Rpi3 this afternoon at work. I haven't messed with it yet. I spend a little time tonight playing with the Moteino M0 + BME280 breakout board. The voltage regulator on the M0 board warms the BME280 board on soldered to the other side of it. So it reads about 4-5F higher than ambient. The problem may go away in the final application when the M0 processor is in standby most of the time and the average current consumption is in the micro amp range. Otherwise I will have to put an air gap between them or change the mounting strategy of the BME280 breakout board.

  8. #8
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    Now I have the gateway Arduino receiving data from the remote sensor node over wireless. The remote sensor node is going into the very low power standby mode, waking itself every 10 seconds, transmitting the temperature, humidity, & pressure data packet, and going back into standby.

    I have it running now while I'm watching the received data in a console window on the PC so I can test if the heating of the sensor by the circuitry on the M0 board is negligible.

    I still need to make the Raspberry Pi 3 talk to the gateway Arduino.

  9. #9
    Not really a Hairy Aussie
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    It's alive!



    The Raspberry Pi 3 is receiving and processing the data from the Moteino (Arduino) on the MightyHat. The Moteino receives the data over the RFM69 wireless transceiver from the Moteino M0 board elsewhere in the house.



    Now it's time to scale this project up and make a lot more nodes. I also plan to put an ambient light sensor on all the nodes.

    MH_IoT_GW.jpg

    dashboard_view.png

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