433.92 MHz receiver - Page 1
Forum section: electronics / beginners

author: m.m.m
author_rank: Regular Contributor
timestamp: June 25, 2014, 07:01:10 pm
content: hi, I have a RF remote controlled wall plug which uses 433.92MHz transceiver, I wanted to make another transmitter for it, and not to spend lots of money, so I bought a cheap 433 MHz receiver to find out the commands and powered it up and connected it to my saleae logic analyzer and started sampling and sent turn-on command from the transmitter, but nothing appeared on the logic analyzer. this is my first RF job and I'm newbie in this section.thanks.

author: lapm
author_rank: Frequent Contributor
timestamp: June 25, 2014, 07:13:51 pm
content: Well there is few ways to encode digital data to carrier. Your receiver might no be able to handle modulation that your transmitter is putting out...And im assuming your receiver actually has antenna to receive rf transmission...Also voltage levels of receiver/logic analyzer may cause some issues... Receivers output circuit can cause issues. For example if for some reason its open collector type, it will not supply any current, but needs pull up resistor. Etc...And this is where oscilloscope would be handy bugger to have...

author: jlmoon
author_rank: Unknown
timestamp: June 25, 2014, 07:26:47 pm
content: In the U.S. that would be an interesting frequency to run a remote on, but we're in the ITU region 2 band plan which requires a amateur radio license to operate.

author: m.m.m
author_rank: Regular Contributor
timestamp: June 25, 2014, 07:48:59 pm
content: thanks, but please take a look at schematics that people use, like this one:http://www.instructables.com/id/RF-315433-MHz-Transmitter-receiver-Module-and-Arduit doesn't use any pull-ups and is directly connected to an arduino.do you mean the receiver on the wall plug can use antennas? don't think so because on the case it says maximum range of 40 meters.I guess the receiver should receive some bits anyway even if it doesn't support the modulation.unfortunately I don't have an oscilloscope yetalso another thing: is it possible for it to don't work because of the power supply isolation? I use an LM317 connected to a linear wall transformer, is it insulated and does it have anything to do with the power supply?anyway I blown up the receiver by connecting the power supply incorrectlyanyway thanks for helping.

author: DavidDLC
author_rank: Frequent Contributor
timestamp: June 25, 2014, 09:22:24 pm
content: I just came across this:http://dangerousprototypes.com/2014/06/25/analysing-433-mhz-transmitters-with-rtl-sdr/I don't know if that will be useful for you, take a look at it.David.

author: poorchava
author_rank: Super Contributor
timestamp: June 26, 2014, 12:35:07 pm
content: You need a certain set of parameters to make your RF circuit to talk to something existing. You need to know center frequency, deviation (in case of FSK), bitrate, modulation scheme and any logic-level conditions that exist.In Europe legal ferquency range lies mostly in 433.05-434.79 MHz range.Modulation scheme can be AM (ASK, OOK) or FSK (2FSK, 2GFSK, 4FSK, 4GFSK, GMSK and many others). Most popular in sub 1GHz ISM bands are 2(G)FSK and ASK.Deviation can be measured with a spectrum analyzer, bitrate can be estimated from deviation.Logic-level conditions may be for example hardware enforced preamble and sync patterns.

author: Kjelt
author_rank: Super Contributor
timestamp: June 26, 2014, 01:17:59 pm
content: Also if you can receive the data don't be surprised if they use some sort of rolling code and MAC on it so then still you will not be able to replicate the transmitterBut perhaps you have an old not secure system, then ofcourse everybody in your neighbourhood can control it.If you don't get the 433MHz to work, just grab the signal before the RF radio, it will be cleaner anyway.

author: G7PSK
author_rank: Super Contributor
timestamp: June 26, 2014, 01:27:27 pm
content: It might just use tone bursts and not transmit codes at all.

author: m.m.m
author_rank: Regular Contributor
timestamp: June 30, 2014, 04:10:04 pm
content: thanks everyone helped, it seems like there are tons of ways to send data over radio.is there anyway to find out which way my device is using by looking at it's board? I can give you the picture of the board of the transmitter. I also have the catalog but it's in german and I guess it doesn't tell anything about the modulation and it only tells that it's in 433.92MHz.

author: m.m.m
author_rank: Regular Contributor
timestamp: July 02, 2014, 09:19:41 am
content: anyone?

author: septillion
author_rank: Newbie
timestamp: July 02, 2014, 09:53:20 am
content: Quote from: m.m.m on June 25, 2014, 07:48:59 pmEvery wireless receiver/transmitter uses antennas. Some small, some large. Otherwise it would be like connecting a lamp without a cable. The one in the instructable is a very common one. But it likes an antenna (wire of about 17cm will work as a simple antenna) to have a bigger gain.Quote from: m.m.m on June 25, 2014, 07:48:59 pmNope, why would it? The receiver will think it's not meant for him an treat it like background noise.Quote from: m.m.m on June 25, 2014, 07:48:59 pmNope, that's the right/save way to go. Your remote isn't connected to mains as well, is it? (Or a car radio...) The transmission is done by airwaves.But as poorchava said, there are tons of different modulations. If you have the transmitter (or receiver) you can try to find the datasheet of the chip and check the modulation. But I have to say, the one in the instructable is very common in Europe (OOK/ASK @ 433.92Mhz). But it's not a guarantee they used it.@Kjelt: I don't think there will be any type of MAC, rolling code or security whatsoever. Most of the sets I know are just simple and indeed a neighbor can control a socket. In fact, it happens a lot :pAnd is it just me or would it be appreciated if you use a Capital at the start of a sentence...

author: lgbeno
author_rank: Frequent Contributor
timestamp: July 02, 2014, 10:03:33 am
content: If the device has an FCC id, look it up on the OET website and read the documentation. There it might get into what modulation is used. Also you can look into the RTL-SDR community and see if someone has reverse engineered it already. If not, if I were you, I'd get an RTL-SDR (like $20) and use GNU Radio to learn to receive the signal first. Once you can receive, you will know how to transmit

author: Psi
author_rank: Super Contributor
timestamp: July 02, 2014, 10:48:43 am
content: There is an opensource RC radio link called OpenLRS. The china copies from hobbyking are quite cheap. $20 from memory.They might be a useful dev platform for playing in the 433mhz band.

author: bookaboo
author_rank: Frequent Contributor
timestamp: July 02, 2014, 10:57:58 am
content: Is it possible to teardown the existing units? They might use a custom IC for all the RF encode/decode, like the old Holtek or the newer Keeloq, that solves all your issues if so as you just buy the chip.Alternatively I see lots of cheap "learning" fobs from China though I have never used one, might be worth a shot.Worst case it could be a custom micro code serial stream, in that case you need a scope and a lot of time.

author: Rasz
author_rank: Super Contributor
timestamp: July 02, 2014, 11:50:44 am
content: just buy RLD-SDR TV tuner, its the cheapest and quickest way to decode those types of transmitters

author: m.m.m
author_rank: Regular Contributor
timestamp: July 09, 2014, 03:11:50 pm
content: I've just bought one, now what should I do? when I press the button on the transmitter, it sends some am-like signals.

author: Rasz
author_rank: Super Contributor
timestamp: July 10, 2014, 02:38:36 am
content: http://goughlui.com/?p=5395http://courses.cs.tau.ac.il/embedded/projects/fall2013/watch-garage-door-opener.pdfhttp://arcanumx.com/?p=44

author: m.m.m
author_rank: Regular Contributor
timestamp: July 23, 2014, 09:03:08 pm
content: thank you for the links, is there any 433.92 MHz SDR decoder apps like this one (which is for linux) for windows os?https://github.com/merbanan/rtl_433

author: othello
author_rank: Contributor
timestamp: July 24, 2014, 03:02:20 am
content: As i'm mostly new to all this and trying to learn, could some one explain what type of equipment would be used to see what kind of signal it is and info it carries ? I see some talk about spectrum analyser, oscilloscope, logic analyser etc.Thank you !

author: Rasz
author_rank: Super Contributor
timestamp: July 24, 2014, 05:36:50 am
content: mmm you can compile it on windows using cygwin for example, or run it inside vmothello all you need is gnuradio, gnuradio is all of those things using rtlsdr. None of equipment you listed would just tell you "bing, its a rc toy #225 remote controller using x modulation, sending y bits". You need to learn to recognize stuff the harder way (by hearing it, trying different parameters etc).another link:http://www.reddit.com/r/RTLSDR

author: bookaboo
author_rank: Frequent Contributor
timestamp: July 24, 2014, 08:13:45 am
content: Quote from: Electronics-Repairman on July 24, 2014, 06:13:47 am433.92 MHz isn't for amateur radio. In most of the world (certainly EU, US and Russia) it's reserved for short range data. Its very common for stuff like remote controls etc.There are various limitations on duty cycle and you are limited to 10mW.Not sure about Israel, they may have different allocations.

author: miguelvp
author_rank: Super Contributor
timestamp: July 24, 2014, 08:17:31 am
content: 433MHz is universal (well at far as the Earth goes) garage door openers and car key fobs among a lot of other short range RF thingies.

author: Wilksey
author_rank: Super Contributor
timestamp: July 24, 2014, 04:47:32 pm
content: Electronics-Repairman:No, you wouldn't, your list states the frequency range as "Digital communications" @ 70cm WL for that matter and as a secondary, look at the ISM bands for Region 1 (UK etc) and you will see that that frequency, along with the 868-869MHz is perfectly usable and would not get anybody's "arse kicked"The only thing you have to be careful of is duty cycle and power output at these ISM band freq's (the powers that be like 10% @ < 500mW, some say 100mW depending on freq).Portable traffic lights, motorway sign communication etc all use these kinds of technology without any prior arrangement from HAM enthusiasts, lots of things share the same frequencies, so it helps to encode it as much as possible, more common is to use a XBEE type interface these days, but all perfectly legal nevertheless, you only suffer from interference if multiple systems on the same frequency are operating the area, thats why it helps to use channels.I have been designing systems with sub 1GHz radios for the past 5 years for the Highways Agency and they have passed every single conformity going (they've had to).

author: othello
author_rank: Contributor
timestamp: July 25, 2014, 12:13:49 am
content: Quote from: Rasz on July 24, 2014, 05:36:50 amThank you, much appreciated !I read something quite a while back about SDR; Could SDR replace those expensive spectrum analysers ? Or what is the big difference ?

author: m.m.m
author_rank: Regular Contributor
timestamp: August 31, 2014, 11:15:34 am
content: Quote from: Rasz on July 24, 2014, 05:36:50 amthanks a lot, I installed Ubuntu, and then installed the rtl_433 app, but it seems like it only supports weather stations, is that right? is there any structure for GNU Radio that does the same thing?again, thanks.

author: m.m.m
author_rank: Regular Contributor
timestamp: September 01, 2014, 11:58:41 am
content: I recorded the signal, here it is:now how can I find out the modulation?

author: m.m.m
author_rank: Regular Contributor
timestamp: September 01, 2014, 07:36:43 pm
content: oh, sorry! silly me! I had to put a simple -a option after the ./rtl-433 command! now it's workin! I've got the code: b0 01 10 : 10110000 00000001 00010000so now I can send it via a 433MHz ASK sender, am I right? if so, then how can I send the data to the emitter? can I use serial port?