Contact sensor inside mailbox - enough range to Gateway?

I’m very new to LoRaWAN/TTN and was hoping to get some support regarding my specific requirement.
I want to put a contact sensor inside the mailbox of my apartment building to receive notifications when new mail arrives.

It seems there is a TTN Gateway quite close to my place (400m):

But the line of sight is not completely uninterrupted. Also the contact sensor must be placed inside the metal mailbox which I guess will drastically influence signal strength. The Gateway is a LPS8, which I understand, is an indoor Gateway and hence not very strong.
Is this doable with an off-the-shelf sensor?

I was looking at the following sensors:

Will all of these work? Which one would be best?
From a functional perspective the CPL01 and MIL-EM300-MCS would be better as they can more easy be fitted inside the mailbox / on the mailbox door.

Thank you in advance. I really appreciate the help.

The chances of a LoRa sensor inside a metal box being received more that maybe 50m away are slim.

Metal boxes are very good at screening RF.

So make the mailbox less of a metal box.

… or bring the antenna - which is the key element - outside the box. I have many sensors deployed in e.g. fridges/freezers for e.g cold chain or landlord monitoring and the LoRa signal does a good job of escaping through what are essentially (from RF POV) leaky seals, but its all construction dependent and YMMV! No one can make a recommendation for you as this really is a ‘piece of string’ question and the only way to know is to test!

Given you are only looking at aro 400 m and a large part of that across an open football pitch and a road etc, unless the pitch is atop a hill in between you may find it works (I get great signals from a Post Office in my village to home office (inc on a dragino LPS8!) which is >800m away with lots of village building clutter (and a small playing field & tenniscourt/bowling green) inbetween - again will depend on the position of the GW (and specifically its ant) dont let fact its an indoor unit deter you - placement is everything! Perhaps if you can contact the owner he/she can help optimise or tell you what appears on associated console etc. to help debug install…

…ofcourse you could always add to community and improve coverage density and grab a similar unit for yourself! :slight_smile:

Changing the mailbox is not possible unfortunately. It’s a fixed unit for the whole house.
Looks like this btw.

Would it make a difference if I stuck some kind of knob on the inside of the door to force it open a bit?
Theoretically the slit is always open when the mailman throws something in but I don’t know how much latency is to be expected until the message is transmitted.

I use a couple of em300-mcs, when the state of the switch changes, it sends a uplink within a second (difficult to measure, if you open/close the switch and look at the console it looks immediately, latency between my gateway and LNS is ~300-800ms)

I have installed them in a couple of places where the clutter is challenging and they work well.

The only way to know will be to test, as your clutter (RSSI) and SNR is unique to your location.

At best, install a gateway and expand the network :wink:

Hi @brintal I’m using this DIY msensor inside a mailbox very similar to yours.

I have a couple of outdoor gateways in the same building, 9 floors above the sensor, one in the same front than the mailbox, and the other in the opposite one, and the uplinks in SF8 are received with -103 ~ -110 RSSI

I have tested that using this kind of antenna can improve the reception dramatically.

You can get a node to wake up, or activate, within a second or two. Wheter this is enough to send a long range packets (circa 1.2secs long) and whether there is enough splatter of the RF through the slot to reach the gateway is somethong you will only resolve with an experiment, much will depend on where the Gateeway is located.

That looks like a dipole, with shorted elements. A standard dipole would have elements around 8cm long. So maybe it has a gain slightly less than a standard 2.1dBi dipole of 1.5dBi or so.

A simple wire would have around the same gain, so if you see a ‘dramatic’ improvement then the previous antennas would have been not so good.

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Yes @LoRaTracker the improvement is relative to the FPC antenna that we usually use with that mailbox sensor

I was curious though, why do you have a GPS on a sensor thats in a mailbox ?

Hi LoRa Tracker, that photo is from a different node; it’s a SOS sensor with geolocation using GPS and WiFi access point MAC through

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That is if you want to test, LOL, he did all the testing for you.

I am sure you can build it with out it. :shushing_face:

Featuring a tried and proven Atmel AVR ATMega328p.
Afaik the ATMega328p is not suitable anymore for LoRaWAN as the libs are too big to fit.

Yes, compiling the basic OTAA ‘hello world’ sketch will report;

“Low memory available, stability problems may occur”