Metal in walls prevents radio communication. Alternatives?



  • After installing the latest weather station node to the roof of the house, I finally found the limits of nrf24l01. First of all there is a need to pass a metal roof but luckily only partially as the weather station is installed on the end of the ridge. However, the biggest problem seems to be the insulation used in the second floor walls and the ceilings as it is polyurethane sheets with thin aluminum foil on both sides. This seems to block all radio communication very efficiently (also WIfi seems to be blocked pretty good). I have set transmission rate to max on the weather station, there are also 100uF capacitator and rate is set to 250Kbs. Also all transmission time intervals are carefully set so that there should be minimal sequential transfers to drain fully the capacitator. Still it works only part of the time, otherwise I get nacks, connection failures. Not power issue because everything works fine right if I bring my gatewat outside the door.

    As the installation of the weather station was very much pain in the butt, I really would like to find some way to get the singnals flying without touching the weather unit.
    Repeater path:

    • As I like to keep my gateway near center of the house, moving it is not an option. So maybe putting some repeater node in strategically good place between weather station and gw.
    • I tried this with one Nano+nrf24l01 repeater combo with transmission strength MAX. Because it was an old sensor node, it took power from Nano's 3.3V which probably is not enough but there was 100uF capacitator compensating that. Anyway, this repeater works fine every place inside the house but don't help a lot when you step outside.
    • So the next step...I have ordered nrf24l01+pa+lna with antenna and plan to try it in a repeater node separately powered and with combination of small and big capacitator. Planning to put this outside very near to the wall appr. 4m to the weather station and 8m to the gw. In that place it would have basically no obstacles to the outside's weather station but to gateway it has to pass those two metal insulation sheets and three drywalls. Will work or not, don't know if I could do anything more with plain vanilla nrf24l01...

    Mixed alternatives:

    • Another option would be some kind of a double antenna solution or mixed serial "don't know if it's even possible" route. The main idea would be somehow receiving the data outside and carrying it inside via cable and then send it wirelessly to the gateway. Any idea how to do that with a single Arduino or is basically two nodes combined required?
    • Also any other idea to overcome this problem would be very welcome.

  • Mod

    @Sushukka maybe an ethernet gateway? Could you pull an ethernet cable through/round the troublesome insulation? Power for the Arduino could use one of the unused pairs in the cable.


  • Mod

    or an esp8266 gateway if you have wifi coverage nearby



  • @mfalkvidd My central gateway is already ethernet gateway. Also wouldn't that mean I should put my GW outside --> all the inside nodes wouldn't be able to connect it anymore.

    @gohan Sadly wifi has also problems when going outside. But could it be possible to use NRF24 with ESP8266 so that:

    • ESP8266 sits inside where is wifi coverage and...
    • NRF24L01 is wired through the wall outside.

    But this would mean that I would need force weather station somehow communicate only with this esp8266. Also would it generate some competition having two gateways in NRF24L01 network?



  • @mfalkvidd said in Metal in walls prevents radio communication. Alternatives?:

    t gateway? Could you

    maybe second ethernet gateway ? is it possible to have two gateways ? there are also solutions for ethernet over power line, e.g. TL-PA4010.



  • Under the mixed section, "double antenna", a passive re-radiator may work. I dont know enough to give details, but it is two antennas connected by a wire. You may have to drill a hole in your wall to pass the wire through.


  • Mod

    @Sushukka No issues, just change channel on one network and you are fine (give at least 10 channel distance from the 2). Maybe you could get away with the PA LNA radio only


  • Mod

    @Sushukka I meant a second ethernet gateway. You said you didnt't want to move the existing one.



  • Weather station has been working lately pretty well. Only sometimes there can be an hour connection break or so. Therefore PA LNA may be just enough. So I'll build an outside repeater based on that and if it doesn't help I have now couple of other paths (double antenna, second ethernet gateway) to go. Thanks again fellow forum members, the community here is one of the most active in this area I have seen! :)



  • Then I might "steel" thread a bit :)

    I want to monitor/count pulses from a power meter. But the thing is that we live in the building and the power meter it is in a "common" metal box (one more meter in it). I can place a device inside and write on it that it is a monitor, but the problem is that meter is inside the completely metal box, with only two wholes, both filled with main power cables. So no holes, no option to get the antenna sticking out of the door, no option to plug it in the power even, it has to run on the battery.

    From my understanding, that box is a dead hole when it comes to external communication. Or? Use the box somehow as an antenna? Telepathy perhaps? :)

    One "ironman" idea is to clamp around one of the main cables inside the box, to somehow send the signal from "around the cable by injecting microwave signal nano particles" and then from inside the apartment which is 4-5m detect injected signal and send it to the gateway.
    But when I make that last thing, then I might as well make the ironman suite...


  • Mod

    @dakipro Maybe a powerline adapter? Or you could make an openenergymonitor and attach in the main switch box of the apartment.



  • What do you mean by powerline adapter?
    All the main switches/fuses and the meter are in the same stupid metal box. Cables come "magically" into the apartment. Thing is that they belong to the "building", and I can only touch things in the apartment (i cannot install 220v socket inside the box f.eks.). All (almost, except for one) the cables come trough the walls and are not accessible

    I could make several non-contact (with the clamp) monitors and attach them around huge appliances, but... that is a plan d (and I do not have plan b or c)


  • Mod

    https://it.wikipedia.org/wiki/Powerline

    But if you can't touch pretty much anything inside that box, it is gonna be hard. Maybe the only option is to make a data logger or a GSM node.



  • yeah that poweline was the one of the ideas (variation on the particle injector from above)..
    I will ask electrician next time he comes if he can install one powerplug inside the powermeter box.
    If he can do that, then I could use it to send data trough the cable to the inside of the appartment, and take it from there.
    I can see daily usage on the power company portal, was hoping to get something more of a real-time-ish



  • @dakipro Have been following the electricians work at my house many years now and tbh not very impressed how delicate or elegant their ways or work are. What I did was:

    • I drilled a small hole to the main electric intake metal box. Just couple of mm small hole and put plastic lead-through so that the metal edges won't wear the cable. Also drilled the hole to the bottom of the box so that there is no way rain or other crap to go in.
    • 5v supply power cable (from mobile or whatever adapter where you can get) through the hole and...
    • put ESP8266 (Wemos D1 Mini) in with LM393 light sensor and little bit modified "PulsePowerMeter" example from Mysensors build page and it has been working flawlessly about one year now
    • There is little to nothing to go wrong as the Wemos is inside it's own plastic box, secured away from everything and the light sensor is just taped on the led of the electric meter.

    So yes, the metal box blocks Wifi signals in some level but not that much it could prevent connection through that metal box, outer wall and one or two in-house walls between my Wifi router. Anyway, you need to get 5V/3,3V power inside the box as batteries don't last very long with ESP8266.



  • If I understand you @Sushukka correctly, you have a esp that connects on wifi in completely metal enclosure, and it connects to your wifi?
    That might give some hope that I can do the same, perhaps with a repeater that can be located ~2m from the box, bein separated by 1-2 walls. I tried directly connecting to the main node, but it didn't work.
    I understood that Nrf24l01+ uses same frequency (or does it?) as wifi so it should work as well.

    I will take a photo of the electrical box, but it is basically like this one
    alt text
    and it is built into the wall in a hallway, sort of like this (ignore these numbers, I just googled for a photo)
    alt text
    (but I can live with rechargeable batteries[hell yeah I can live without the pulse meter, but "I need one" :) ])



  • @dakipro My experiences so far are that even the frequencies with NRF24L01 and ESP8266 are nearly same ESP8266 tend to have better range and communication reliability than NRF24 (even with PA+LNA and caps). Because of architectural differences ESP8266 draws however more energy and really wouldn't rely on batteries with it.

    Anyway in your case it seems that the box is little bit thicker than mine hence it probably dampens the signal somewhat more. If I were you, I would just bring the 5V in and by looking those pictures it shouldn't be hard. Currently I have only two battery operated nodes and they are freezer/fridge temperature sensors based on Sensebender. When you are going to have tens and tens of nodes around the house, the battery replacements start to get out of control. So after bringing 5V in, build just a standard Arduino or ESP8266 node. If the signal is not reliable enough, then bring (if using ESP8266) your wifi router closer or MySensors gateway (if using Arduino/NRF24). Of course you could use ESP8266 with Arduino but nowadays with Wemos Minis and similar complete boards, it's kind a dummy move. If putting up another Wifi extender or moving your Wifi router is not an option, just stick with the Arduino/NRF24. After finding out how far the NRF24 can reach with caps and MAX signal strength, you can set a repeater node in strategically selected position if required.

    However, if the box dampens the signal very heavily I would just keep the Arduino+light sensor in the box and wire the NRF24 part out of the box (using the same hole where the 5V comes in). Then you would need to build just one node and probably don't need to move any routers/gateways outside.



  • thanks, I will try it soon when I grab some time/motivation.
    Photos above are from google, here is the actual box in the common hallway

    0_1504637971934_20170905_204828.jpg

    And it is common box for two apartments, so no drilling possible, batteries only :)


  • Hardware Contributor

    You could still try a PA LNA module with ipx antenna and bring antenna outside of the box, metal should be flexible enough to let the cable get out on one side. And no need to activate pa/lna mode so it can live longer on battery.


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