RF Detector

xanaduxanadu Posts: 3,058
edited July 27 in Propeller 1 Vote Up0Vote Down
I'd like to be able to detect radio freqs between 10 kHz to 200 kHz, using the Propeller and an antenna. I'd imagine there would be a few other components.

I recently started riding a 250cc motorcycle, and on a 90+ degree day, getting stuck at a red light trying to turn left is the worst. Not only does the bike have very little metal, it has a lot of ground clearance (dual sport).

This is the type of traffic signal I'm typing about - https://en.wikipedia.org/wiki/Induction_loop

This is what I want to do - http://www.ebay.com/itm/Motorcycle-Green-Light-Trigger-Traffic-Light-Activator-Red-Light-Changer-New-/332153452418

I figured I would start with a Propeller data logger, with an antenna and try to detect frequencies, for fun, as a learning exercise, and then later hopefully to be able to transmit some of these frequencies. I am hoping to use a large AM loop antenna for now. The antenna calculator says I'd need one twice the width of my bike, which is another hurdle.

Does anyone have a starting point for me, maybe some code and a circuit that could pick out a higher than normal RF signal in the 10 kHz to 200 kHz range?

Edited, I can see how this could be confused with attempting to do something illegal, disrupt signals, etc. The guy running the eBay auction is no dummy, and did a lot of research. Although this is not illegal in any way, I am not building any transmitter of any sort, only a detector.
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  • The eBay listing mentions "U.S. Department of Transportation published specifications". Could you look at those?

    You need one of the de-gaussing loops the RAF used to explode mines during WWII!
    WELLINGTON-DWI-bw.jpg
    South Saxons - "we wunt be druv".
  • That ebay seller may not be totally correct. FCC licensed spectrum goes down to 8.3KHz. If I'm reading this FCC table correctly:
    https://transition.fcc.gov/oet/spectrum/table/fcctable.pdf

    Also, the claim that the device only "Makes the motorcycle visible" is dubious. That may be true. On the other hand it can be construed as intentionally causing interference to another electronic device.

    I would think carefully before setting about building any such transmitter.

  • Perhaps I should have left the eBay link out. The first and foremost step is detection, rx only.
  • Heater.Heater. Posts: 19,354
    edited July 27 Vote Up0Vote Down
    OK.

    I'm actually interested in the idea of "detecting the loop detectors". It is something I was thinking about some years ago when I had a need, professionally, to find loop detectors. Or to get an idea if they were working correctly. That need might arise again.

    I'd be inclined to just build a VLF loop antenna and look what comes out of it. It will probably need some kind of amplifier and filtering. I was thinking of following some of the VLF antenna descriptions that can be found around the net. For example: http://www.vlf.it/easyloop/_easyloop.htm


  • Perfect, thank you. I ordered a few OP27 and a can of yellow spray paint.

    The county highway department says they cannot make the inductive loops more sensitive because of things like rain, high humidity, and snow. They also mentioned that they ride motorcycles and understand the frustration. They told me the loop at the end of my street is 200 kHz, so I have something to calibrate the rx.

    I'm going to try building my own traffic detector so I can test various things against it. Something like this but using uC instead of the 555

  • It's tricky. If the loop detector is too sensitive it can be triggered by vehicles in adjacent lanes. This confuses the control systems. Especially when a detector of traffic approaching an intersection is triggered by vehicles leaving the intersection.

    Years ago when I was working on a new central control system with new radar vehicle detectors I could also see the old loop detectors firing as well. Comparing to the radar tracking I could see that quite many of them were false triggers. The old control system had been confused for years before and nobody knew or cared!



  • Yeah I'm starting to see why something like a motorcycle has a hard time. I started wrapping a 50' extension cord around my patio table for my own loop. I have an LC meter around here somewhere.

    I'm missing one diode and one cap to build that detector in the youtube video. I want to compare mass vs proximity. There seems to a lot of debate on some motorcycle forums, and very little testing going on. Another topic of debate is the use of magnets to trip the sensor, again, no real testing going on there either.

    All of this makes me wonder how these inductive loops are in use. Watching the amount of effort that goes into cutting lines in the road, and all of the associated hardware has to be more expensive than a few cameras. It seems kinda like buying a beam balance scale instead of a digital scale. Or, just put in a roundabout and no signals are needed.

    Here's a fun traffic simulator - http://www.traffic-simulation.de/
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 21,044
    edited July 27 Vote Up0Vote Down
    xanadu wrote:
    Yeah I'm starting to see why something like a motorcycle has a hard time.
    My town's stoplight-trigger loops have a pair of lines painted on the pavement in the middle with a bike symbol. If you park a bicycle with its tires on the lines, it will trip the signal. Otherwise, no dice.

    -Phil
    “Perfection is achieved not when there is nothing more to add, but when there is nothing left to take away. -Antoine de Saint-Exupery
  • xanadu wrote:
    Yeah I'm starting to see why something like a motorcycle has a hard time.
    My town's stoplight-trigger loops have a pair of lines painted on the pavement in the middle with a bike symbol. If you park a bicycle with its tires on the lines, it will trip the signal. Otherwise, no dice.

    -Phil

    That's what I need! I was told by a civil engineer that left-turn pockets have more coils, specifically for bicycles. The most problematic intersection for me is brand new and should have the more sensitive loops installed. Unfortunately, at this intersection they installed the loops before sealing it, so I have no idea where the loops are.

    Despite being accused of trying to make an RF red light changer that works at a long distance, I had a lengthy conversation with a traffic engineer. I told him everyone knows you use IR to change lights and he didn't think that was funny either. He did point me in the right direction on a lot of items, and there's lots of documentation out there I didn't know existed. This PDF is pretty cool - http://www.dot.ca.gov/hq/esc/oe/project_ads_addenda/07/07-294704/plans/07-294704_plans-pgs 101-192.pdf

    I took an AM radio antenna and attached it to an inductance meter and made a lot of observations that are probably very obvious to most people here, but it was a lot of fun. I can also see why some things work for some people and not for others.

    More on that later.

  • The Front end of this circuit works extremely well for what you want to do.... It basically is an emitter follower where the BASE of the transistor is fixed, and the actual input is on the EMITTER of the transistor. Since you don't know the exact frequency you will need to remove the capacitor that is in parallel with the sense coil so that the receiver becomes a broadband receiver. With this circuit I was able to sense an RFID door reader and decode the tag from 20 feet away with a 3.5 inch diameter coil tuned to 125kHz. All you need is the front stage "Regen Detector" ... the transistor COLLECTOR is the output and could be connected to a scope for testing.

    http://www.kit-start.com/RFID Receiver/RFID receiver_html_mf57f20d.jpg



    Beau Schwabe -- Metallurgical Machine Design and Development Engineer
    ෴My Message෴www.Kit-Start.com - bschwabe@Kit-Start.com ෴෴ www.BScircuitDesigns.com - icbeau@bscircuitdesigns.com ෴෴

    "I've said it before ... If you follow the directions for apple pie and then expect it to taste like cherry pie then your absolutely insane"
  • Nice, thank you. I have the parts.

    For my antenna, I need 10 to 200kHz range. Should I make the antenna based on 200kHz, or the middle of the band?
  • MikeDYurMikeDYur Posts: 2,052
    edited July 28 Vote Up0Vote Down
    xanadu wrote: »
    Here's a fun traffic simulator - http://www.traffic-simulation.de/

    You can see where the breaking can become contagious, and cause a traffic build-up for no real reason.

    I started a huge construction project at the end of a long curve, caused one heck of a traffic jam. Going to see what happens when the track is crossed or try the New Jersey bridge maneuver, and play a little longer.



  • I would start with a mid range coil of 100kHz ... and then maybe 50kHz and 150kHz ... With this design you can switch out coils pretty easily, but remember without a capacitor in parallel you'll mostly just be receiving broadband (<-- Everything)

    I'll just open this page up I created about 3 years ago ... There are a few helpful files to calculate winding your own coils under "Additional Resources"

    visit:
    http://www.kit-start.com/

    Navigate to the tab that says "Enter the RFID sniff project instruction Page"
    The password is "reddirt" and you need to press the "Submit" button... the ENTER key will not do it.



    Beau Schwabe -- Metallurgical Machine Design and Development Engineer
    ෴My Message෴www.Kit-Start.com - bschwabe@Kit-Start.com ෴෴ www.BScircuitDesigns.com - icbeau@bscircuitdesigns.com ෴෴

    "I've said it before ... If you follow the directions for apple pie and then expect it to taste like cherry pie then your absolutely insane"
  • xanadu wrote: »
    I told him everyone knows you use IR to change lights and he didn't think that was funny either.

    I know someone who painted their Land Rover in IR-absorbing paint from a military-surplus shop. He thought it looked "cool" - but spent an awful lot of time waiting at traffic lights.
    South Saxons - "we wunt be druv".
  • What is all this nonsense about IR?

    I might presume that "IR" means some kind of Infra Red communication.

    In my two decades of involvement in traffic engineering in Scandinavia and now the USA I have never seen any such IR technology in use.

  • Heater. wrote: »
    What is all this nonsense about IR?

    I might presume that "IR" means some kind of Infra Red communication.

    In my two decades of involvement in traffic engineering in Scandinavia and now the USA I have never seen any such IR technology in use.

    https://en.wikipedia.org/wiki/Traffic_signal_preemption#Line-of-sight

  • I would start with a mid range coil of 100kHz ... and then maybe 50kHz and 150kHz ... With this design you can switch out coils pretty easily, but remember without a capacitor in parallel you'll mostly just be receiving broadband (<-- Everything)

    I'll just open this page up I created about 3 years ago ... There are a few helpful files to calculate winding your own coils under "Additional Resources"

    visit:
    http://www.kit-start.com/

    Navigate to the tab that says "Enter the RFID sniff project instruction Page"
    The password is "reddirt" and you need to press the "Submit" button... the ENTER key will not do it.

    Thanks for all of the help. When I click the link I get a page that says "Hacker Detected." As much as I'd like to think of myself as a white hat, I'm more of an application support guy hehe.

  • xanadu wrote: »
    Heater. wrote: »
    What is all this nonsense about IR?

    I might presume that "IR" means some kind of Infra Red communication.

    In my two decades of involvement in traffic engineering in Scandinavia and now the USA I have never seen any such IR technology in use.


    https://en.wikipedia.org/wiki/Traffic_signal_preemption#Line-of-sight

    Those are normally used for emergency vehicles to set the lights to red all ways.
    Infernal Machine
  • Publison wrote: »
    xanadu wrote: »
    Heater. wrote: »
    What is all this nonsense about IR?

    I might presume that "IR" means some kind of Infra Red communication.

    In my two decades of involvement in traffic engineering in Scandinavia and now the USA I have never seen any such IR technology in use.


    https://en.wikipedia.org/wiki/Traffic_signal_preemption#Line-of-sight

    Those are normally used for emergency vehicles to set the lights to red all ways.

    Yes and that's pretty old school these days. Many of the current preemption schemes for emergency vehicles use GPS location, speed, travel direction and the turn signal indicator of the vehicle as inputs to the traffic control device management system. In my locale the vehicle parameters are transmitted by RF data link to the main system and the traffic lights, etc., are all on a fiber network. It works well in my experience.
  • Beau SchwabeBeau Schwabe Posts: 6,275
    edited July 30 Vote Up0Vote Down
    xanadu wrote: »
    Thanks for all of the help. When I click the link I get a page that says "Hacker Detected." As much as I'd like to think of myself as a white hat, I'm more of an application support guy hehe.

    It has to do with your network, and how some computers are configured that it does not like .... I had to write this page with odd security guidelines for the Las Vegas presentation I gave.

    Try this instead ....
    http://www.kit-start.com/Source Code/
    http://www.kit-start.com/RFID Exciter/
    http://www.kit-start.com/RFID Receiver/
    http://www.kit-start.com/RFID Decoder/
    http://www.kit-start.com/RFID Make it Work/RFID making it work.html

    BTW) This isn't really RF ... it's closer to Near field magnetic coupling. <-- Such a Google search might produce better results

    The "Exciter" mimics the Door Scanner you would normally place your TAG on .... The "Receiver" simply listens (at a distance) for a modulated signal.

    The "Sniffer project" was to exploit a security vulnerability in the current technology where a conventional RFID Door Scanner becomes the transmitter when a tag is placed on it. Even the so called "smart tags" used in hotel keys that negotiate a communication between the tag and the door reader are susceptible because this kind of receiver can "Listen" to both sides of the conversation. One of the requirements for the Sniffer project was to use common "off the shelf" components which makes the exploit even more alarming.

    Under optimal conditions and with an exceptionally tuned coil I was able to correctly read a tag placed on the exciter that was 20 feet away from the receiver. I have since improved this distance, but I can't release the schematics anytime soon. We haven't even scratched the tip of the iceberg, I'm working with a guy at the DOD on a project that may require a change in the entire infrastructure down to the checkout line at the grocery store.





    Beau Schwabe -- Metallurgical Machine Design and Development Engineer
    ෴My Message෴www.Kit-Start.com - bschwabe@Kit-Start.com ෴෴ www.BScircuitDesigns.com - icbeau@bscircuitdesigns.com ෴෴

    "I've said it before ... If you follow the directions for apple pie and then expect it to taste like cherry pie then your absolutely insane"
  • Can I ask what about my network it doesn't like? I am sitting behind a Fireware UTM, maybe it was trying to hide some info. No proxy or VPN action.

    Oh wow, you forced me into an RBL check and sure enough my IP is listed. Arg. It's dynamic for crying out loud. This RBL is only for email, I suppose you can use any RBL on your webserver you want.

    I have to look at this tomorrow. My brain is kaput right now. Hopefully that's not a problem. Thanks again :)
  • RF = "radio frequency", not "radio waves", so perfectly appropriate to apply to near-field situations.
    Quite whats RF is a pretty elastic thing anyway, radio amateurs have used 8.7kHz transmissions
    across the Atlantic for instance (I needed a calculator to figure out that that's actually far field!)

    I guess RF implies sine wave, not digital, but who knows if inductive vehicle sensors are actually
    sine not square wave anyway(!)
  • Mark_T wrote: »
    RF = "radio frequency", not "radio waves", so perfectly appropriate to apply to near-field situations.
    Quite whats RF is a pretty elastic thing anyway, radio amateurs have used 8.7kHz transmissions
    across the Atlantic for instance (I needed a calculator to figure out that that's actually far field!)

    I guess RF implies sine wave, not digital, but who knows if inductive vehicle sensors are actually
    sine not square wave anyway(!)

    Agreed, but I usually don't think of magnetic coupling as being Radio Frequency, but you are right. I just wanted to make sure that we understood that this particular application was indeed magnetic coupling and not quite the same as using a radio antenna.

    My research experiments are analogous to detecting a refrigerator magnet spinning at 7.5 million RPM (125kHz) at a distance of 15 to 20 feet away with a 3.5 inch diameter coil. Not an easy task .... I guess if you had nothing more than a spinning magnet, it could also be considered a "transmitter".




    Beau Schwabe -- Metallurgical Machine Design and Development Engineer
    ෴My Message෴www.Kit-Start.com - bschwabe@Kit-Start.com ෴෴ www.BScircuitDesigns.com - icbeau@bscircuitdesigns.com ෴෴

    "I've said it before ... If you follow the directions for apple pie and then expect it to taste like cherry pie then your absolutely insane"
  • I haven't found your antenna calculator. I have an RFID antenna, so I'm going to take that, the circuit and my pocket scope for a walk later today and see how well it works.
  • I'm a little surprised that this project hasn't been mentioned: http://forums.parallax.com/discussion/105674/hook-an-antenna-to-your-propeller-and-listen-to-the-radio-new-shortwave-prog The antenna input will, of course, need to be changed.

    I wonder if it's necessary to receive the signal and transmit a reduced frequency version, or just sweep the transmitter over the full range.
    James https://github.com/SaucySoliton/

    Invention is the Science of Laziness
  • I had to get into a local university car park, which was a pain as it wanted a card - but I saw that there was a loop detector over on the inside. By getting out and sticking a tool box over there the barrier would raise - I then noticed that if I stood in the right place, or marched about, the metal in my boots would do the same (cue Silly Walk imagery).

    Perhaps riding the bike whilst wearing deep sea diving boots ...
  • I had to get into a local university car park, which was a pain as it wanted a card - but I saw that there was a loop detector over on the inside. By getting out and sticking a tool box over there the barrier would raise - I then noticed that if I stood in the right place, or marched about, the metal in my boots would do the same (cue Silly Walk imagery).

    Perhaps riding the bike whilst wearing deep sea diving boots ...

    I was thinking about adding a few layers of thick foil between the boot and Insole. I have some special foil on order, thicker than the thickest aluminum foil stores sell. Thin enough to not be noticeable.

  • Does it require a ferrous metal since it is a magnetic loop?
    Jim
  • RS_Jim wrote: »
    Does it require a ferrous metal since it is a magnetic loop?
    Jim

    The AI foil was only a reference to thickness. I ordered iron foil online.
  • xanaduxanadu Posts: 3,058
    edited August 1 Vote Up0Vote Down
    It seems like any type of metal will change the inductance of my test loop. I would imagine that ferrous metals have more of an effect, but non-ferrous metal has some effect.

    Metal detectors can detect both.
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