Which radio / wireless module to choose? Please recommend



  • Hello,

    (sorry if this is a duplicate but I could not quite find answers for my questions)

    I would like to build radio/wireless sensors running on battery and I am not sure what radio / wireless modules to choose. I would like to achieve:

    • sensors based on Arduino Pro Mini 3.3V or 5V (I like the size)
    • sensors powered by 9V battery (seem easy to connect and powerful enough to me)
    • about 7 or 10 temperature sensors inside my house (13m x 7m 2 stores)
    • if possible I would like to put simillar sensors approx 50m from the house inside beehive
    • not too expensive as ( plan to buy about 10 modules )
    • easy to solder/connect to standard 2,54mm DPS

    My idea was to put the gateway to attic at the side were the beehives are.

    I prefer to use same module for everything but from some forum post I got impression that the GW might better use different module?

    Should I use LoRa mode or FSK mode?

    Could someone please recommend modules I should buy? And what kind of antenna?

    In case you have some comment for my preferences I will be happy to head them as I am new to this.

    Thank you very much

    Tomas


  • Mod

    The nrf24 radios are lowest cost, about 13 usd for 10 modules. They also have shortest range (10 to 50m depending on a lot of factors) and largest risk of interference from other devices since it uses the same frequencies as wifi and bluetooth. No need to solder, you can use dupont wires directly or a socket.

    The rfm69 radios are the middle ground. About 15 usd for 10 modules. Can be bought for different frequency bands (433MHz, 868MHz, 915MHz). Different regions in the world allow different frequencies, so you'll have to share where you are or find what the law says for your area. Range is approximately 20m to 100m. These are generally harder to solder since they don't use 2.5mm. Using easypcb can be a simple solution.

    LoRa radios can also be bought for different frequencies. They cost about 37 usd for 10 modules. If you pay the extra royalty to Semtech for LoRa, do not use FSK. If you plan to use FSK, go with rfm69. Range can be up to several km in the right conditions, but it will depend a lot on the local radio environment. rfm95 and rfm98 are examples of LoRa radios.

    A 9V battery is not a good choice. The regulator on the arduino will burn off 2/3 av the available power, so you'll have a physically big battery with very little practical capacity. Look at https://www.mysensors.org/build/battery instead.



  • @mfalkvidd Thank you for your suggestions! Can I please have additional questions?

    Can be bought for different frequency bands

    I am in Europe/Czech Republic so it should be 433MHz / 868MHz. Is there any difference between these two especially regarding range / antenna complexity?

    Should I look for specific chip vendor or is the quality all the same?

    Could you help me understand why different modules for GW and node are mentioned by @NeverDie said in Second setup, choosing a radio ? I can reach every corner of our property with a RFM69HCW on the GW and a non-amplified RFM69CW on the node.

    If you pay the extra royalty to Semtech for LoRa, do not use FSK.

    Do I understand it correctly that LoRa technical parameters (especially power consumption and range) are better than FSK mode (altough more expensive and lower throughput - but that is probably not important for transmitting few numbers)?

    ( I already have two SX1278 433Mhz chips and two SX1276 868Mhz chips that I bought for testing. But I was little bit disappointed when I found out that RH_RF95 does not support the FSK mode as it limited my options to choose what mode to use. Also I notice that 433Mhz modules were provided with a little different spring antennas than 868Mhz ones. )

    A 9V battery is not a good choice.

    I do not understand the electricity stuff much more than + - and number of volts (discovering Arduino onboard regulator was like Christmas for me!) so I wanted to keep things simple (not to add additional modules like step up convertor) and better give a bit more juice than less (I am not sure how would all the sensors and radio module work with 2x1.5V). Would the 9V really so inefficient? What about 3x1,5V?



  • @tssk said in Which radio / wireless module to choose? Please recommend:

    I prefer to use same module for everything but from some forum post I got impression that the GW might better use different module?

    Your Gateway has to use the same radio as your nodes to communicate. Generally speaking the easiest and simplest Gateway is identical to your nodes, connecting by serial to your Controller.
    It is the Controller which has to be a more powerful device such as a Pi, it and the Gateway will live in the same box and will run 24/7 on mains power, usually communicating via a router.

    Your Controller+Gateway should be accessible, so would not recommend putting it into a loft with no easy access.
    If your reasons for the location are radio communications (to the hives?), a 433MHz RFM will penetrate walls with ease...

    Further to the point made by @mfalkvidd on batteries, a 9v wastes 60% of it's capacity on a 3v3 Node, 2xAAs will actually have a higher mAh capacity.
    All my Nodes have 2xAA and are still going after 2 years..



  • @zboblamont The reasoning for putting the GW in the attic were:

    • most of the sensors I plan would be in the house level just under which has wooden ceiling so there would be good connection

    • if ignoring one brick wall there would be "line" of sight to the beehives position

    • I have no problem going to attic in case something breaks on the GW and it would be connected by ethernet sending data to MQTT broker

    But I would like to use as good communications modules as possible because in the future I would like to add more sensors around the house where also thick concrete ceilings are. And I would not like to run anither type of radio for that.



  • @zboblamont said in Which radio / wireless module to choose? Please recommend:

    All my Nodes have 2xAA and are still going after 2 years..

    So you think that something like Arduino Pro Mini 3.3V + DHT22 or BME280 + 433/868 radio module would run on 2x1.5V AA battery ok? No extra components (like step up) or modifications like removing LED or regulator from Arduino?



  • @tssk A basic pro-mini clone needs modified (VR and LED), but with a few mods can run direct on batteries to fairly low voltages.
    I bought these modules in as it would have cost more to make them even I was skilled enough (I still ain't), but they are essentially 3.3v Pro-mini with an onboard booster, regulator, rfm69 and various other refinements which gave it the edge over a Moteino.
    Sundberg84's board might be an alternative worth considering, plenty of knowledge on it and help always at hand.

    As to sensors, have a DHT22 somewhere but never deployed it when I found DS18B20s did all I required on a single run of Cat5e throughout the house and the outside, a second line covers the boiler.
    I went for the 433MHz version of the RFM from the start, it easily passes through multiple masonry and concrete with a quarter wave antenna, so your floors may not be the problem you think later. The higher the frequency, the more attenuation effects you encounter, if .433 is permitted in your country I'd recommend it.



  • I have tried the nRF24 and sx1278 and have had success with both. I ended up choosing the sx1278 even before exploring the world of mysensors mainly because I really liked the library by Sandeep Mistry. I never had an issue with range. In my old apartment I collected pulses from my electricity meter which was located four concrete stories below without a problem.

    Regarding the 9V battery I also did some experimenting with this and the key, if I remember correctly, is to find a VR with very low Iq( quiescent current). In the end I ended up going with dual AA batteries which worked to a surprisingly low voltage. There is a lot written about battery powered electronics if you start to dig a little bit.


  • Hero Member

    No matter which one you pick there are tradeoffs. For instance, one of the nice things about the nrf24 is that you can update your mysensors sketch over-the-air. If you have dozens of nodes which need updating, that's a big convenience and time saver.



  • @tssk said in Which radio / wireless module to choose? Please recommend:

    Arduino Pro Mini 3.3V + DHT22 or BME280 + 433/868 radio module

    Hello, I am going to take my first steps with the MySensors library. I found this Mega328p + RFM69HCW kit:
    https://www.aliexpress.com/item/33006101437.html?spm=a2g0s.9042311.0.0.3f774c4dIx4PVw
    xrobotix RFM69HCW.jpg

    I find this development board interesting:

    • accepts many RFMs
    • possibility of soldering an antenna wire or SMA or uFL connector.
    • No voltage indicator led, but a 3.3v regulator (which can be unsoldered). A blue led connected to a gpio.
    • known 328p microcontroller (arduino compatible)
    • connector for FTDI
    • possibility of soldering an additional FLASH ROM
    • many gpio available

    I am waiting for the schematics and software included, from the seller to say more. For now, the blue led flashes once powered on, but no return to the serial link ... I will post more news if the topic is requesting 😉


  • Hero Member

    @SuperNinja Looks like a copy/variant of the Low Power Lab's module, which is a good design because it offers the option for extra flash memory (to facilitate OTA programming) using their dual bootloader.



  • Indeed, now that you say it, it looks a lot like Moteino.
    Anyway, I can't wait to see my first "hello world" appear on my screens. I will see later for the OTA with double bootloader, that will be the icing on the cake 🙂



  • I would like to thank everyone for suggestions and comments.

    I did 3 quick tests with two SX1276 based chips (868MHz LoRa) I already had.

    I made simple 5V poe powered mysensors mqtt gateway with arduino pro mini 3.3V, W5500 lite and SX1276 radio
    test-gateway.jpg

    Simple 9V battery powered mysensors passive node with arduino pro mini 3.3V, BME680 (for some reason the sensor does not work when connected over SPI with the radio module at the same time - I have to investigate that ) and SX1276 radio
    test-node.jpeg

    First test was inside house - I placed the node inside the freezer on the opposite side of house (approx 15m from gw) with concrete ceiling between. All messages were delivered.

    Second test was outside the house - I placed the node under the beehives (approx 50m from gw). All messages were delivered.
    test-ok.png

    Third test was also outside the house - I placed the node at the end of our property (approx 140m from gw). But no message was delivered.
    test-notok.png

    I expected 140m would not be problem for LoRa chip but I think this may be improved with some antenna fiddling. But overall I am very happy with the results. So my current decision is to go with this setup but to use 2 or 3 1.5V AA batteries instead of 9V.



  • @tssk That is promising news and thanks for the update.

    For the longer distance try a yagi antenna (bought or homemade) - It should make a fair difference.

    As for the batteries, they will suffer a lot in colder weather. Consider rechargeables with solar or wind to charge them up. Alternatively make them easily removable to recharge in the house and reinstall.

    Also think about effects of damp or humid weather. Corrosion will happen in these instances so some form of conformal coating or other 'tropicalisation' treatment would be recommended. A fully sealed box with O-rings or silicon gunk might also be an option.



  • @skywatch Thanks for tips. I do not think there will be any problem with inhouse - nodes. And regarding the nodes in beehives - I expect that bees maintain +10C at least. But that is one of the things I want to find out 🙂

    Any experience with silica gel packages in the box with node?



  • @tssk Not with silica gel no, my only experience was back in 2014 when I used the nrf library (not my sensors) to send data from my greenhouse back to the house to monitor temp and humidity.

    The power supply in a sealed box was fine and never overheated (but ofc low power usage). The promini and nrf24 however were not so lucky and were heavily corroded within 4 years.

    Since my greenhouse is only 2m x 3m it was not worth the time and expense of doing a full system sealed for the high temps and humidity it gets in the summer months.

    I just wanted to save you some trouble down the line (probably in winter when it's snowing). 😉



  • @tssk So long as your box is near enough sealed, dried gel or clay packs are effective in drying the trapped air even if the box is occasionally opened for say reprogramming.
    If the packs are permanently exposed to external air they will quickly saturate and cease to be effective.
    I prefer clay packs as they can be quickly regenerated in a microwave if you're very careful.


  • Hero Member

    @tssk The gold standard is two part electronics waterproof potting epoxy, though for some reason it's rather pricey.

    As a much cheaper alternative, I've been running outdoor tests on Corrosion-X HD since the beginning of the year, and so far it has safeguarded the open-to-the-atmosphere internals of Chinesium solar garden lights that, without protection, would ordinarily rust-over and die within a mere month or two. It does have one noteworthy advantage over hard epoxy: you can slot in a new rechargeable battery if/when needed.

    @zboblamont said in Which radio / wireless module to choose? Please recommend:

    @tssk So long as your box is near enough sealed, dried gel or clay packs are effective in drying the trapped air even if the box is occasionally opened for say reprogramming.
    If the packs are permanently exposed to external air they will quickly saturate and cease to be effective.
    I prefer clay packs as they can be quickly regenerated in a microwave if you're very careful.

    How does one do it carefully?



  • @NeverDie Short blasts while keeping an eye on the bag, the steam vents off quite vigorously stretching the porous bag but having only one perhaps I'm overly cautious with 15 second bursts...
    If I ever get spares may test one to 'destruction' in the micro, but it is way faster re-generation than traditional slow oven, 10 mins v 2 hours..
    Clay grains survive the nuking intact, silica beads don't 🙄 ...



  • I finished gateway for my attic - What did you build today (Pictures) ?:

    As this will be under roof but without any isolation I try to put small silica gel bag (I collect them from other electronics packaging) inside and will see. I think it should be suitable. I am thinking of adding temperature and humidity sensor... that could also help me show how much humidity is around the year actually.

    I might use the resin / epoxy stuff for some watering projects 🙂


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