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Building a Remote Control

littwentythreelittwentythree Registered User
edited May 2008 in Help / Advice Forum
How would I go about building a radio-wave remote control?

I've been thinking about this over the last few months. The parking lot to my apartment complex is protected by a large fence and a gate that is controlled by a remote control. The ones they give us are mostly worthless, usually you have to get outside of the car and stand three feet away just to get the receiver to notice that you've done anything.

But I digress. Long story short, it raised my interest in just how you would go about building a remote that could send messages on a frequency. Could anyone link me to some type of guide?

Don't talk about illegal uses of remote technology in this thread. Thanks.

littwentythree on
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Posts

  • littwentythreelittwentythree Registered User
    edited May 2008
    Really, nothing? H/A has yet to fail me.

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  • littwentythreelittwentythree Registered User
    edited May 2008
    Up to the top one last time.

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  • ecco the dolphinecco the dolphin Registered User regular
    edited May 2008
    If it were me, I'd purchase an RF transmitter/receiver pair (or transceiver if bi-directional comms. was required) and build a circuit around it. Sparkfun has a wireless section for hobbyists, if you're interested.

    Typically what happens is that the RF aspect of the deal is abstracted away for you, so all you need to do is send a serial stream of data. There may be some configuration involved, but that is dependent upon the hardware.

    Penny Arcade Developers at PADev.net.
  • littwentythreelittwentythree Registered User
    edited May 2008
    A lot of that went over my head, but I'll see what the website has to say. Thanks.

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  • mspencermspencer Registered User regular
    edited May 2008
    Aha, caught the thread before it escaped. I'm a ham radio operator and I think I answered one of these posts once before, by someone else.

    There are a few design considerations I should hear about before I suggest a technology.

    First, receiver requirements. For what you want to build, how sensitive are you to nuissance triggers, malicious unauthorized triggers, or failed trigger attempts? There are some things you can legally and easily build for not a lot of money, but it'd be easy for someone to record your transmission and play it back later.

    (So for example, it wouldn't be cheap or necessarily SMART to do this, but you can legally build a transmitter and receiver pair with frequency and effective radiated power set so you can trigger your device from the other side of the planet -- but any radio ham could record your signal and play it back any time they wanted, and then THEY could also trigger your device from the other side of the planet.)

    Where would this receiver be installed? Could you possibly colocate the receiver with a PC and let software on the PC do the work? Or does the receiver need to be a self-contained device?

    MEMBER OF THE PARANOIA GM GUILD
    XBL Michael Spencer || Wii 6007 6812 1605 7315 || PSN MichaelSpencerJr || Steam Michael_Spencer || Ham NOØK
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  • littwentythreelittwentythree Registered User
    edited May 2008
    What receiver? I didn't ask about building a receiver, I don't think.

    What is apparent is that what I'm talking about is complicated, and that I am very naive on the entire subject. The OP was about building some type of remote that would have the ability to trigger something such as a garage door.

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  • ecco the dolphinecco the dolphin Registered User regular
    edited May 2008
    When you want to send signals/data/information of any form over the radio waves, you will always have a "transmitter" to send the information that you want, and you will always need a "receiver" to... well, receive the information that was sent.

    Thus, if you want to build a remote control of any sort, you will need at least one transmitter and one receiver.

    I unfortunately don't know or have any beginner level resources on wireless comms/radio networks, so can't provide any recommendations on what to read up on, I'm afraid.

    Penny Arcade Developers at PADev.net.
  • littwentythreelittwentythree Registered User
    edited May 2008
    Well, obviously the remote controlled garage door already has a receiver. I'd just be building a transmitter. And doing this on my home garage, because doing so on someone else's would be illegal.

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  • cyphrcyphr Registered User regular
    edited May 2008
    I think he's saying that he wants to use the existing receiver on the gate, and build a remote control with a stronger signal that sends exactly the same information as the current (worthless) remote control the landlord gave him.

    But I don't know anything about RF stuff, so beyond that I've got nothin.

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  • ecco the dolphinecco the dolphin Registered User regular
    edited May 2008
    The trouble is knowing exactly what to transmit. Even if you were operating on the exact same frequency, the way the command to open the garage door is transmitted is an unknown right now.

    If you wanted to build a remote control to open your garage door, you'd have to find out that information. I haven't looked into garage remotes, so I couldn't tell you if there's some sort of common standard that they adhere to. Things to investigate!

    Penny Arcade Developers at PADev.net.
  • littwentythreelittwentythree Registered User
    edited May 2008
    Exactly what he said(cyphr). But I think I would try it on a friend's garage or something, since now that I think about it doing something like that might be illegal.

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  • mspencermspencer Registered User regular
    edited May 2008
    Well, there's "transmit a signal on a frequency" and then there's "transmit a specific signal that will cause a specific transmitter to react."

    To answer the original question: if you're transmitting something that can be represented in binary and you don't need a lot of speed, then you need: an RF frequency generator circuit, something to turn the signal on and off according to a pattern you create, a transistor-based linear amplifier circuit, and an antenna. The frequency generator is just an audio oscillator but instead of outputting, say, 500 hz (like for an audio tone) it needs to output, for example, 147,495,000 hz. The thing to turn the signal off and on again could be one of those programmable microcontrollers, I don't know. The transistor linear amp is just a few cheap radio shack parts, and the antenna can be just a straight piece of wire cut to half the wavelength of the signal you're transmitting. (468 divided by frequency in mhz is the number of feet for a half-length dipole antenna.)

    Or if you're transmitting something wider-band, like an audio signal, you could use amplitude modulation. You need the same RF frequency generator circuit as above, some kind of audio-frequency signal source (a tape player or MP3 player would work for that), a signal mixer (mixing the RF signal and the audio signal), plus the same transistor linear amp and antenna as above.

    (If you actually build either of the above out of plain electronics parts, you earn the label "ridiculously and perversely old-school". Bonus points if what you build (not counting antenna) fits inside an Altoids tin.)

    Something purpose-built to trigger a specific receiver requires a bit more planning and intelligence gathering. You're probably going to ask about this next.

    MEMBER OF THE PARANOIA GM GUILD
    XBL Michael Spencer || Wii 6007 6812 1605 7315 || PSN MichaelSpencerJr || Steam Michael_Spencer || Ham NOØK
    QRZ || My last known GPS coordinates: FindU or APRS.fi (Car antenna feed line busted -- no ham radio for me X__X )
  • mspencermspencer Registered User regular
    edited May 2008
    Also, while MAYBE illegal depending on how the FCC interprets the term 'modification' if your transmitter has an external antenna (piece of straight metal that sticks out of the body) you could in theory build a goofy looking Yagi-like passive element array around the active element your transmitter already provides.

    Someone technical would need to do some quick math and give you precise numbers to cut various pieces of metal and plastic, but essentially you would build something large and awkward you would attach to your antenna. Technically you'd just have pieces of metal floating out in space, and nothing but plastic would be touching your original antenna -- but you'd be turning a dipole (which radiates in all directions more or less, in a kind of donut shape) into a yagi (which is much more directional but has to be aimed at the receiver).

    Probably not worth doing.

    MEMBER OF THE PARANOIA GM GUILD
    XBL Michael Spencer || Wii 6007 6812 1605 7315 || PSN MichaelSpencerJr || Steam Michael_Spencer || Ham NOØK
    QRZ || My last known GPS coordinates: FindU or APRS.fi (Car antenna feed line busted -- no ham radio for me X__X )
  • littwentythreelittwentythree Registered User
    edited May 2008
    Alright, I can understand what you're saying. To even begin doing something like that I would first need to figure out just what triggers the specific brand of garage door receiver I'd be trying to send a specific signal to. And even after that, I'd probably have to get past some kind of security measure.

    This sounds like a very involved process, and I would probably have to start off with something simpler just to understand some of the basic concepts that go into it. I have absolutely zero experience.

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  • mspencermspencer Registered User regular
    edited May 2008
    Indeed. I have a few ham friends with expensive equipment that could help -- spectrum analyzers, wideband receivers, etc. -- and I know I would need their help if I were to try to clone an existing garage door remote transmitter. I also know they probably wouldn't help me, and their opinion of me would be damaged, because garage door frequencies are outside the amateur band and they know I know better.

    Hell, I'd be proud of myself if I could make my own AM transmitter like the one I described, without burning myself with the soldering iron. Just because I technically kinda know how doesn't mean I CAN. :-)

    MEMBER OF THE PARANOIA GM GUILD
    XBL Michael Spencer || Wii 6007 6812 1605 7315 || PSN MichaelSpencerJr || Steam Michael_Spencer || Ham NOØK
    QRZ || My last known GPS coordinates: FindU or APRS.fi (Car antenna feed line busted -- no ham radio for me X__X )
  • ecco the dolphinecco the dolphin Registered User regular
    edited May 2008
    Have you considered trying to get a "universal garage remote" instead of building your own? Unless you're really interested in building your own, that is. =)
    mspencer wrote: »
    Hell, I'd be proud of myself if I could make my own AM transmitter like the one I described, without burning myself with the soldering iron. Just because I technically kinda know how doesn't mean I CAN. :-)

    Heh, I just buy mine off the shelf. I let people far better than I deal with impedence matching and all that.

    Penny Arcade Developers at PADev.net.
  • littwentythreelittwentythree Registered User
    edited May 2008
    The crappy remote is a non-issue, what this is really about is "Oh, so that's how that works. Neat."

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  • mspencermspencer Registered User regular
    edited May 2008
    If you're really interested in learning about RF -- if like I used to, you think of "how do people make custom radio transmitters to do anything they want" as special forbidden powerful knowledge that you crave -- you might consider studying ham radio stuff. Maybe. The general idea here is: the FCC still believes that "how to build and fix radio stuff" is knowledge that should never die, should never become the patent-encumbered realm of cell phone companies and the like exclusively. There should be a pool of radio amateurs with no commercial interest in radio who stay trained in this stuff, to advance the art/science in interesting ways, provide public service where needed, and several other reasons.

    Essentially it's like the FCC has taken "the hacker ethic" (as regards radio at least) and encoded it into federal law. There's a LOT of amateur spectrum and LOTS of things we can do with it, and nobody can take it away from us without literally an act of Congress. All of it becomes pretty silly looking once you have an Internet connection, but this is about learning and about personal empowerment. (Plus once you understand this stuff, you'll never have to worry about, say, getting stranded in the snow somewhere with no cell phone service and having no way to reach anybody.)

    Keep in mind, though, there's a whole industry of radio equipment and clubs and organizations and whatnot that will try to latch onto you once you get your license. Some of it might be useful, but you don't need all of it. (My personal involvement has led me to my local county government's ARES (amateur radio emergency service) group. I've taken severe weather spotting classes, and in fact I'm one of the on call volunteers for my county this week, where if there's severe weather I come to the courthouse basement and help man the phones and radios. Once they finish my ultra-low-priority background check I hear I'll get an access card for the courthouse doors 24x7.)

    So you could decide you just want some knowledge and then you won't care to continue. You can spend $75-ish on some study books, pass tests all the way up to Amateur Extra (which tests you on lots of electronics stuff, and gives you legal access to ALL amateur spectrum), maybe buy the ARRL's antenna reference book, and then kinda drop out and take your knowledge and run.

    I can offer pointers on where to start (for cheap) if you'd like, but most people find this stuff kinda boring and pointless. (Until a hurricane or other natural disaster disrupts normal communications, and then people briefly remember why there are still hams.)

    MEMBER OF THE PARANOIA GM GUILD
    XBL Michael Spencer || Wii 6007 6812 1605 7315 || PSN MichaelSpencerJr || Steam Michael_Spencer || Ham NOØK
    QRZ || My last known GPS coordinates: FindU or APRS.fi (Car antenna feed line busted -- no ham radio for me X__X )
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