RF Remote Made Easy

The 433 MHz spectrum is a little bit of an oddball. It’s one of the few areas of the radio spectrum which is nearly universally unlicensed Outside of the US, it’s an open playground for devices that adhere to the power restrictions and other guidelines about best practices. IoT devices operate here, as well as security systems and, of course, remote controls. And, using a few off-the-shelf parts [hesam.moshiri] shows us how to take advantage of this piece of spectrum by designing and building a programmable and versatile 4-channel 433 MHz remote control.

Built around an ATmega8 microcontroller, making it easy to work with Arduino sketches, and with a 2×8 character LCD for ease-of-use when not connected to a computer, the wireless switching device can store up to 80 remote control codes in its EEPROM memory. This was one of the harder parts for [hesam] to sort out, but using structures to store the data for the codes eventually solved the problems. A simple GUI makes using it with whatever remote happens to be on hand fairly straightforward, including the ability to record codes from existing remotes on the fly and also to associate those codes with specific actions.

Schematics and a bill of materials are available on the project’s page, making this fairly accessible to those looking to add some wireless connectivity to a project, home automation system, or IoT device. It’s mainly set up as a switching device, but with some modifications could be put to work doing more complex tasks. The 433 MHz spectrum is an exciting place to be, too, and things like setting up entire security systems using it are not too far removed from a switching device like this.

[Editor’s note: As many mentioned in the comments, 433 MHz is a licensed ham band in the USA (ITU Region 2), so you can’t use it without a license. (Get one, it’s easy.)  In the USA, the equivalent band is at 315 MHz, which is why garage door remotes usually come with a 315/433 choice. Either way, check your local laws before you transmit.]

10 thoughts on “RF Remote Made Easy

  1. 433 MHz is absolutely NOT an ISM frequency in ITU Region 2. It is not legal anywhere in the North or South America to operate a 433 MHz transmitter without a licence.

    433 MHz happens to land square in the amateur radio 70 cm band there though, so if you hold an appropriate ham licence you CAN transmit (but without encryption).

    Conversely, if you DO transmit there without a licence, be aware there is a large community of people who are very defensive about that band, and make a hobby of direction finding rogue transmitters. And, if caught, the fines are large.

    1. I don’t think I heard ISM in the video, maybe I missed it.

      You’re absolutely wrong though. 433mhz transmitters are covered under 47 CFR § 15.231. Look up any garage door opener, weather station with remote probe, or wireless security system sensor on FCC.gov.

      It’s certainly not the only overlap with amateur bands, they’re not exclusive use.

      1. Part 15 allows operation at low power and/or low duty cycle on pretty much any frequency (limits vary by frequency).

        Legitimate 433 MHz transmitters sold in the US will carry a FCC certification for allowed use. It’s not a free-for-all. You’re not allowed to build your own (unless you’re a ham with a suitable grade of license). Similar rules apply in other Region 2 jurisdictions.

        Realistically, if you are an individual that has a transmitter that operates under Part 15 rules and doesn’t happen to be type-accepted (carry a FCC cert), then it’s not going to result in any action against you (unless you’re being a jerk with it).

        1. On that side of the big pond they have a similar “free for all” frequency band. I think it’s around 315MHz, as the cheap 433MHz modules generally are also available in that frequency range. But I don’t live there and don’t know the details.

      2. Yup. For example, Lutron Caseta uses FSK on 433.92 in the United States.

        Hams do have priority over unlicensed, but it’s not exclusive. Just like hams have priority over unlicensed in the 2.4 GHz band in theory – in practice no ham operates there unless running a high-power point-to-point link because it’s such a cesspool of interference from so many sources that your priority can’t realistically be enforced.

        Hams also have MUCH higher power limits in all shared bands – unlicensed 433 MHz operation has a very low power limit, hams can go up to over a kilowatt in most if not all of the 70-cm band as long as they meet the requirements to do so (hold a license, periodic on-air identification with your callsign, severe limits on encryption to the point where it’s basically no encryption allowed).

        Wikipedia is dead wrong on this one.

  2. From his YouTube video, it would appear that the code writes “1234” into every location of the eeprom on startup. Unfortunately, the way this has been written would cause it to be done on every single power up of the system so you’d have to reprogram it every time you had a power cut or changed the batteries (depending on your power source).
    It would perhaps be better to suggest commenting that line out after the first run, or make it so you have to hold a button down on reboot to wipe the stored codes, otherwise each time setup() is called, your current key values will be toast, since the programmed ones in the struct array != 1234.
    Interesting project though.
    The links in the YouTube video and hackaday.io article both seem to link to a precompiled hex binary but he briefly outlines the code in the video itself.

  3. I get so little use out of my General class license these days; I should pick up some cheap 433MHz stuff and then look smug when people tell me it isn’t actually unlicensed.

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