Go Down

Topic: RF tips to my project?  (Read 282 times) previous topic - next topic

kjetilhansen

Jul 11, 2018, 10:19 am Last Edit: Jul 11, 2018, 12:30 pm by kjetilhansen
Hello all :)


I am trying to make a project that notifies me when I receive mail in my real mailbox. But as I live in a concrete building and the mailbox is about 100 meters away, what is the best RF solution?

I bought two HC-12 modules, after seeing test, it seems like they are not that good to penetrate building..

I just bought two SX1278, they might be right for me.. Do these need a library or can it be used via RX/TX and Serial.begin();?

What long rage module would you recommend when the signal needs to travel about 100-150 meters and through two buildings?

srnet

What long rage module would you recommend when the signal needs to travel about 100-150 meters and through two buildings?
SX1278.

Do a google search on 'Arduino LoRa'
$50SAT is now Silent (but probably still running)
http://www.50dollarsat.info/
http://www.loratracker.uk/

silly_cone

Properly formatted, an NRF24L01+PA+LN may also provide the necessary distance.  Those can go up to about a km, but have some caveats that need to be accounted for, such as additional shielding when transmitting at that power.

Robin2

Properly formatted, an NRF24L01+PA+LN may also provide the necessary distance.
Very unlikely if the HC12 modules won't work. Lower frequencies travel better.

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

silly_cone

Would it be the building causing the drop in signal rather than the distance itself in this case?

srnet

Would it be the building causing the drop in signal rather than the distance itself in this case?
You tell us.

Are you suggesting that the drop in signal through buildings is uniform, regardless of frequency ?

You might expect that the higher the frequency the more the affect of free space, buildings, forests etc.
$50SAT is now Silent (but probably still running)
http://www.50dollarsat.info/
http://www.loratracker.uk/

silly_cone

Oh I'm not suggesting anything, just curious and wanting to learn more.  The NRF modules I mentioned can do up to about a kilometer in open-air, so my assumption is that they would likely be able to transmit 1/10 of that distance through structures.

I'm by no means an expert on the interaction of frequency and permittivity (if that's even the right word, lol).

srnet

The NRF modules I mentioned can do up to about a kilometer in open-air, so my assumption is that they would likely be able to transmit 1/10 of that distance through structures.
On what basis have you made the assumption ?

If a TX\RX pair were capable of say 1km in open air, with a very good clear line of sight between TX and RX, then my assumption would be that the reception distance would drop to 1/1000th of that distance in and around urban areas and maybe 1/10000th (or less) through structures.

$50SAT is now Silent (but probably still running)
http://www.50dollarsat.info/
http://www.loratracker.uk/

silly_cone


Srnet, I'm just basing that off how the NRF's I have at home behave indoors compared to outdoors where there doesn't seem to be a hugely significant drop-off in distance.  With the normal dinky little PCB-trace antennae and no special care taken to antennae-orientation or shielding, I get a pretty reliable 40-50-ish feet of transmission, and indoors I easily get around 30 feet.  So that's only a decrease of about half. But that is through a residential home made of 2x4's and sheet-rock, certainly not concrete, steel, or stone.

But I'm a little perplexed by your statement of 1000x - 10,000x decrease in distance.  So if something goes 1,000 meters in open-air, you'd only expect it to transmit 0.1 - 1.0 meters in an urban area?  These things use the same frequency as wi-fi, and its not nearly as delicate as those numbers would imply.

Not trying to get in a pissing match or anything, just trying to learn and square my experience with the knowledge of those more knowledgeable than myself.   :)

srnet

#9
Jul 12, 2018, 08:51 am Last Edit: Jul 12, 2018, 11:12 am by srnet
Best to look at it from the perspective of long distance.

If you have a radio system that is capable of say 500km with very good line of sight, say ground to high altitude balloon or ground to space, then the same system will likely have a range of 500m or less at ground level in an urban area.

Distances within buildings are normally much less than you will get at ground level (outside) in an urban area.  
$50SAT is now Silent (but probably still running)
http://www.50dollarsat.info/
http://www.loratracker.uk/

Robin2

2.4 GHz wireless transmission is greatly affected by the substance through which it must pass. Things with moisture and metals can absorb a lot of energy. Remember that microwave ovens work at 2.4GHz - so don't expect an nRF24 to transmit through a Ready Meal.

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

kayel

 If you just want to know if it's possible, try it.

 http://www.picaxeforum.co.uk/blog.php?do=list&page=2

 OPL-Transmitter.ino and OPL-Receiver.ino are the ones you want.

 You'll need the SX1278 datasheet to understand the code.

 What's legal in your country is your problem. My code is legal in mine.
 
 I used two Arduino Pro Minis (5V models) at 3.3V and got 250 metres range through three of my neighbours' houses.

 I'm sure I could have done much better with the right parameters, but whenever I tried to read up on radio transmissions I kept waking up with "AZERTY" printed on my forehead. So don't bother asking me any questions. I don't know, and don't want to.

 You were already talking to the right people before I butted in.



 

silly_cone

Thanks for clearing that up, Srnet and Robin2.

Go Up