Arduino Signal Detector

Hi everyone!

I hope I'm not posting in the wrong place, but have done some research and need a little guidance.
After a few successful projects I am trying something new (at least for me).
I know very little about radio signals / cell signals / frequencies etc. but would like to create a "detector" for these signals.
I do not want to trace, sniff, communicate or anything - merely have my arduino light up an LED once any signal is detected across a broad spectrum.

A few things to note after research:
-This will be in the Arizona desert - so no or very little interference
-I'd like to pick up a walkie talkie or a cell phone - maybe only when it's in use?
-I do not want to record location of signal
-trying to maximize detection range. I'm thinking anenna(s) of 1-2' length?

Anyways, any direction would be great!

Thanks in advance.

I don't have any specific suggestions about how to design such a circuit. But I can tell you about an important general principle that will affect it. A simple wideband receiver, that covers the huge range of frequencies you describe, would have a very low sensitivity indeed. It might only be able to detect signals a short distance away.

To have the level of sensitivity you are probably hoping for, the receiver circuit would have to have a very narrow frequency band which it would need to scan over a wider range. This would be a very complex and difficult circuit to design. I'm not sure if anyone on this forum has that level of expertise. You might have better luck on an amateur radio enthusiast forum.

One suggestion I do have. If you want to detect WiFi signals, get an esp based board with the ability to attach an external antenna. Get the highest gain non-directional antenna you can for it, but beware that lots of exaggerated claims about gain are made by cheap suppliers. Sketches are available which will scan the WiFi channels and you could modify one of those to light an led.

merely have my arduino light up an LED once any signal is detected across a broad spectrum.

Wire the anode of an LED to the +ve terminal of a battery and the cathode to a 220R resistor with the other end of the resistor to the -ve of the battery. So the LED is on all the time. This is because all the time you can pick up some radio transmitter from somewhere in the world.

Now think about what you actually want to do in a bit more detail, because that request is just impossible. There is no way to know if a signal received is a weak signal from nearby or a strong signal from a long way off.

Grumpy_Mike:
Now think about what you actually want to do in a bit more detail, because that request is just impossible. There is no way to know if a signal received is a weak signal from nearby or a strong signal from a long way off.

Whilst practically true, technically the uplink and downlink frequencies are often different. It does very much depend on which RAN standard you’re using though…

Out of pure monkey curiousity, why do you want to do this?

Thanks everyone for your responses! I really appreciate all the insight and you have now awakened my inner Don Quixote.

I’ll answer the first question last so as not to seem completely monkey crazy lol. I have some private land often times have a few wanderers on dirtbikes, atvs or some hikers come through.
I am an avid rider myself – so don’t mind the riders one bit or that they are traversing through – it would just be cool to “pickup” a signal -> my own curiosity I suppose.

For the next question – is it possible to focus on the “walkie talkie” range first, then perhaps cell or wifi?
Again I’m not interested in tracking or even communication. I’d like to focus in on those spikes (uplink, etc.)

Grumpy_Mike – do you mean miles (or 100s of miles)? For a long way off? I’m ok with a baseline “noise” for those signals that I can experiment with in a smaller distance (1sq. mile?)
Paul – thanks for the great info! I guess in the end it’s like a “mayday” receiver or reverse walkie talkie? Always listening but then lights up when a spike in signal happens…

FYI – there is little to no cell signal. While I’d like to look for these too they are not the most important, at least for my 1st round :slight_smile:
If I could build a simple thing that could pick these up it would be fun for me!

I’ll keep on my research but really appreciate any more insight! Thanks guys

"you have now awakened my inner Don Quixote"
So this is a windmill you will be tilting at?

Sounds like maybe you just need a radio scanner to monitor the frequencies of interest.

or, maybe re-think some other mode of detection.... seismic? audio??

do you mean miles (or 100s of miles)? For a long way off?

A long way off is totally relative.

In an open environment the strength of a radio signal decrees with the square of the distance. So if you receive a signal of a specific strength you don't know if it is 1 mile away or 100 miles away because you don't know the power it was being transmitted at. It could be either. What that means is that it is impossible to say that you only want to detect signals within a mile ( or what ever ) radius.

I would go along with cross roads and say get a radio scanner. If you want a wider range of frequencies then go for a Software defined radio like this one SDR

However, your other problem is frequency bands. There are several bands that a walkie talkie can use so it is not easy to cover them all. The problem is that antenna are only good over a small range of frequencies and a walkie talkie can use 27Mhz, 49MHz, 446.0MHz and 900 MHz. Those are only the main ones, their are others.

You guys are incredible! Thank you so much for the help - I was literally lost in an internet vortex of bad info.

SDR sounds VERY interesting and I suppose that's where my thoughts for an Arduino based module came from.
Perhaps this?

Combined with that USB receiver? Or just with another antenna perhaps? Then at least I can get a start tinkering :slight_smile:

Seems like SDR can tune from "24MHz to 1850MHz" so if I can essentially plonk my arduino in the middle of nowhere, then an umbrella or bell of surrounding noise will show on SDR software...when a spike(uplink) occurs I'd be able to see it (?) puuurrree theory

SDR can pick up cell signals as well then? So 2 birds one stone?

Again, I don't want to tune or anything, just kind of "see" a frequency range or the full spectrum...

Phew! You guys have been great so far!

Perhaps this?

https://www.elektormagazine.com/labs/software-defined-radio-sdr-shield-for-arduino-150515-1

Well that one only covers 150kHz up to 30MHz so not much good for what you want.

then an umbrella or bell of surrounding noise will show on SDR software...when a spike(uplink) occurs I'd be able to see it (?) puuurrree theory

Yes you could program it to do that. However, you have no guarantee that any signal is local to you, although the higher the frequency the more sure you can be. A lot depends on propagation which changes with :- the time of day, the seasons of the year, the sun spot cycle, solar storms and meteorites trails, to name but a few.

Hi everybody,

I have an urgent question that perhaps relates to the topic of Boom5lang. I need to find a way to communicate to an Arduino the presence, on a specific location, of GPRS frequencies. I don’t need to quantify the strenght of the signal, just the presence of GPRS fields.
I am not an expert of Arduino at all, but this module should somehow be integrated with an Arduino UNO.
Can somebody suggest a way to go for it? And, in order to detect the signal, do you think I would need a SIM card? Thanks to everybody in advance.

One can always work an Arduino into a project in some manner, but if the most practical and inexpensive route to build a RF scanner is likely rtl-sdr based software running on a Raspberry Pi or similar.

A pure Arduino solution probably involves building your own UHF receiver or modifying an existing product and someone who could do that would likely not be asking this question.