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Topic: Anyone hear of RF field disturbance?  (Read 618 times) previous topic - next topic

prologikus

Ok, so i'll like to know more about this" rf field disturbance technology" as described by some car alarm systems.

What i know about it it's that when a person get closer to the car, without even touching it, this devices sense your presence by rf signals and trigger the alarm.
But what i don't know is how it actually works?
And.. Is there a way to reproduce this device circuit? (because it seems like there is nothing on internet that i can found about it)

Power_Broker

I think you should be searching about "RFID" technology. There are even some Arduino sensors that imitate this behavior and are frequently used for automated door locks controlled by Arduinos. I'm not really up on the technology, but I think it all works on magnetic induction. The fob usually has a coil of wire that is used to (I think) both power the fob circuitry and communicate with the other sensor. Some googling on "RFID" might prove better info than my answer.
"The desire that guides me in all I do is the desire to harness the forces of nature to the service of mankind."
   - Nikola Tesla

prologikus

#2
Jul 31, 2017, 01:02 am Last Edit: Jul 31, 2017, 01:03 am by prologikus
I think you should be searching about "RFID" technology. There are even some Arduino sensors that imitate this behavior and are frequently used for automated door locks controlled by Arduinos. I'm not really up on the technology, but I think it all works on magnetic induction. The fob usually has a coil of wire that is used to (I think) both power the fob circuitry and communicate with the other sensor. Some googling on "RFID" might prove better info than my answer.
"Radio-frequency identification (RFID) uses electromagnetic fields to automatically identify and track tags"

Thieves don't usually wear tags :D :D ..

This module only detects if anything perturbe a big area around the car
"Vper alarms" describe it as:
"Protect your vehicle with an invisible sensing field which detects moving high-density objects (including people) near your car"

EDIT:
"Field-disturbance sensor: A restricted radiation device which establishes a radio frequency field in its vicinity and detects changes in that field resulting from the movement of persons or objects within the radio frequency field. Examples: microwave intrusion sensors; devices that use rf energy for production line counting and sensing."
source: https://www.its.bldrdoc.gov/fs-1037/dir-015/_2216.htm

INTP

It's called radar. I think it came about in WW2.

jremington

#4
Jul 31, 2017, 01:32 am Last Edit: Jul 31, 2017, 01:34 am by jremington
They are probably similar to these microwave Doppler detectors, or this one.

Very cheap and remarkably sensitive! They will respond to a human moving anywhere in a 5m x 5m or larger room.


8bitbacon

What you are looking for is a capacitive sensor for the arduino. If the cars body is metal you just connect that sensor to your cars body and when you get near the car it will give the arduino higher readings
arduino mini woot

prologikus

#6
Jul 31, 2017, 02:19 am Last Edit: Jul 31, 2017, 02:27 am by prologikus
They are probably similar to these microwave Doppler detectors, or this one.

Very cheap and remarkably sensitive! They will respond to a human moving anywhere in a 5m x 5m or larger room.


WOW, very cheap, perfectly for me
I will bought some to check them out ..

EDIT: but which one ?
EDIT2: do you have any idea if the metal of the car will reduce the detection of this module ?

What you are looking for is a capacitive sensor for the arduino. If the cars body is metal you just connect that sensor to your cars body and when you get near the car it will give the arduino higher readings
Yes, this would be perfect ! Do you have any names for the modules ?
Edit: but how exactly this will work ?

GoForSmoke

Everybody has an electric field. Perhaps pumping it with RF makes it more detectable, like a metal detector does with coins?
1) http://gammon.com.au/blink  <-- tasking Arduino 1-2-3
2) http://gammon.com.au/serial <-- techniques howto
3) http://gammon.com.au/interrupts
Your sketch can sense ongoing process events in time.
Your sketch can make events to control it over time.

Shortdood

How far did you get with this?  Did you go the capacitive route?  I'm looking into a similar project.  I'd like to use the human capacitive disruption to any RF field, but I'm not even sure what that is called.  Same principle behind the Theremin, or what happens when you tune in a radio station, but then loose it when you walk away.  I'd like to be able to sense a disturbance, within 1 meter, of the source and send a trigger voltage.  Radars, and IR would be a chore because I'd need to use multiple for 360 degree coverage, where a field would be messed up regardless of where the interference is coming from.  I figure I can regulate the range based on the strength of the field (weaker would be a closer area where interference would occur).  If there are other posts that cover this idea, please forward.

GoForSmoke

#9
Mar 09, 2018, 03:05 am Last Edit: Mar 09, 2018, 03:07 am by GoForSmoke
If you change/move an electrical field you get a magnetic field even if you're pumping square waves.

RF is radio. If you would disrupt, you'd have to match the frequency to a major degree *at the receiving antenna* which will be tuned to that frequency or very close. You'd have to cover bandwidth and likely deal with the FCC or similar if your disruption spreads far at all.

When your field 'couples' with the radio or tv antenna, you become part of it. If you tune for that then when you go sit down...?

There are many lessons and tutorials on electric fields and capacitance on the web. If they don't show working the formulas out, they're intro or less, you need to be able to calculate strengths at distances or you will just flail around and possibly come to wrong conclusions. I sometimes visit a site called hyperphysics for the formulas, pictures and explanations.

Theremin.... lots of web pages about those too. And metal detectors in general, IIRC you can tune them for other things.
1) http://gammon.com.au/blink  <-- tasking Arduino 1-2-3
2) http://gammon.com.au/serial <-- techniques howto
3) http://gammon.com.au/interrupts
Your sketch can sense ongoing process events in time.
Your sketch can make events to control it over time.

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