How to make a simple 433mhz detector for car key fob testing? - Page 1
Forum section: electronics / rf-microwave

author: Chriss
author_rank: Frequent Contributor
timestamp: April 17, 2019, 10:44:42 pm
content: Hi!I would like to make some sort of testing equipment for me for testing the car key fob is it sending any signal or notwhen I let's say press the door lock/unlock.Some time when I repair these type of key fob electronic it is really hard to test if it is ok or not.I have to go to the car and test it.I would like to make a device what could detect the sent signal from the key fob and let's say a led should blink up or some buzzing sound from a speaker or whatever.I don't need any fancy stuff.What would be a good and simple solution for such of device?Any idea or schematic would be nice.Thank you very much.

author: tautech
author_rank: Super Contributor
timestamp: April 17, 2019, 11:13:17 pm
content: What gear do you have ?Any 300 MHz scope or spectrum analyser can do this with just a non-contact RF loop.

author: Chriss
author_rank: Frequent Contributor
timestamp: April 17, 2019, 11:15:06 pm
content: No, I don't have any spec. analyzer or even a scope like you mentioned.I own a 2 channel 50MHz DSO from Siglent.

author: tautech
author_rank: Super Contributor
timestamp: April 17, 2019, 11:19:52 pm
content: Quote from: Chriss on April 17, 2019, 11:15:06 pmI haven't got a 50 MHz scope here to check for you.At max sensitivity and fastest timebase you might see something with the remote held close I dunno. Try, you might get lucky.

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 17, 2019, 11:33:21 pm
content: Quote from: Chriss on April 17, 2019, 10:44:42 pmhttps://www.ebay.com.my/itm/Wireless-433MHz-Radio-Transceiver-Transmitter-Receiver-Module-Remote-For-Ard-N6E/113566555799?hash=item1a71181e97:g:I8QAAOSw5pRcQDiT

author: Chriss
author_rank: Frequent Contributor
timestamp: April 17, 2019, 11:53:12 pm
content: I tried before with my scope but now way to pick up anything.My dso is too lazy to pick up that speedy signals.A very interesting module that stuff on ebay.Thanks for the link!

author: tautech
author_rank: Super Contributor
timestamp: April 18, 2019, 12:01:37 am
content: I had ongoing trouble with a garage door remote in that it wouldn't stay on frequency and I was endlessly tuning it back on frequency with a spectrum analyser.Some mention in another thread about old reference crystals drifting made sense and so we replaced it with some cheap learning remote .........a couple of minutes for it to learn the code and save it has relieved all the forking around I was doing and reduced stress levels dramatically.I've threatened to give the old remote the sledge hammer treatment however there's something yet to be learnt from it when I have some spare time.......it's not like I haven't got the gear.

author: Chriss
author_rank: Frequent Contributor
timestamp: April 18, 2019, 12:14:06 am
content: If I got it correct I could use only the receiver module from this link:https://www.ebay.com.my/itm/Wireless-433MHz-Radio-Transceiver-Transmitter-Receiver-Module-Remote-For-Ard-N6E/113566555799?hash=item1a71181e97:g:I8QAAOSw5pRcQDiTAnd on the data pin I could set a transistor powering a LED or so?I assume the receiver would represent the received signal from the key fob also in a higher frequency something like 350-450MHz range...So I could not use my scope to see the signal.Am I right?

author: eliocor
author_rank: Unknown
timestamp: April 18, 2019, 12:15:34 am
content: Use any SDR USB receiver like this one:https://www.amazon.com/RTL-SDR-Blog-RTL2832U-Software-Defined/dp/B0129EBDS2/ref=pd_sim_23_2/132-7062738-6132838?_encoding=UTF8BTW, you can find similar receivers for much less than the link shown...

author: Chriss
author_rank: Frequent Contributor
timestamp: April 18, 2019, 12:22:00 am
content: This is a really good solution!I could also play with this tool more convenient.Thanks for this nice idea.

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 18, 2019, 03:11:29 am
content: Quote from: Chriss on April 18, 2019, 12:14:06 amyes use receiver only. pin out will toggle high as long as there is 433Mhz. transmitter usually will toggle 433MHz on and off at some rate, say 10Khz, i guess key fob is the same. So this lower rate (data) can be seen on the receiver's pin out. You can use dso or mcu to read this signal. You can also use low pass rc filter to act as averaging to turn on led using transistor, it will dim slowly when no more 433Mhz. But that thing can easily pickup random noise signal so test in clean room is advisable.

author: bitseeker
author_rank: Super Contributor
timestamp: April 18, 2019, 05:25:50 am
content: Quote from: eliocor on April 18, 2019, 12:15:34 amYep, that's the solution I chose a few months ago (got the RTL-SDR V3) for the same reason (verify RF remote). And it's great for other stuff, including listening to the radio.

author: Lord of nothing
author_rank: Super Contributor
timestamp: April 22, 2019, 02:12:39 pm
content: should I post a Picture how the 433 Band look? A ordinary LED Indicator would blink or even light the hole time.Dont buy andthing from the Spam Company No.1 aka Amazon!!!I use many of them and the are good:https://www.ebay.de/itm/NESDR-SMArt-Premium-RTL-SDR-Set-w-0-5PPM-TCXO-Aluminum-SMA-R820T2-RTL2832U-/162115103170?hash=item25bed029c2

author: Amper
author_rank: Frequent Contributor
timestamp: April 23, 2019, 10:40:19 pm
content: There is really simple rf detector chips from analog devices, They are 300MHz-7G giving you a simple to work with analog out signal depending on rf power. Maybe you can just get a cheap breakout with one of them. The advantage would be that youd also have some indication if the range may be a problem.

author: bitseeker
author_rank: Super Contributor
timestamp: April 23, 2019, 11:59:06 pm
content: Ah, good to know. Thanks, Amper.

author: Psi
author_rank: Super Contributor
timestamp: April 24, 2019, 12:03:49 am
content: The keyfob remotes that are static code (eg not code hopping/rolling code) are very bad, in so so many ways.They just look for a pattern match within the data.So a stream of bits are coming in, noise or signal etc.After each bit comes in it checks if it's secret code matches the last 8 bits.Rince/repeat.There is no start/stop tracking at all!Check out this video, quite interesting

author: Chriss
author_rank: Frequent Contributor
timestamp: May 07, 2019, 08:50:18 pm
content: Hmmm this is an interesting video and moves my main post in a different but interesting direction.I have two questions:1. What is that software Samy used on his PC to measure the signal? ( something like spectrum analyzer )2. What is that radio device connected to the usb port on his laptop?

author: Psi
author_rank: Super Contributor
timestamp: May 08, 2019, 08:25:05 am
content: Quote from: Chriss on May 07, 2019, 08:50:18 pm1) Either a;- SDR (Software Defined Radio) in spectrum analyzer mode. They cost ~$20Or- USB radio, like the YARD Stick Onehttps://www.amazon.com/dp/B06Y1RVHBP/ref=as_li_ss_tl?psc=1&linkCode=sl1&tag=blileytech04-20&linkId=d4d5888367f79b9f8257a5df2f4dba35&language=en_US&linkCode=w61&imprToken=cEg4YgsHDMb9ofLR2agt9w&slotNum=52) Dunno, Some sort of USB radioIt needs to transmit so a cheap $20 SDR isn't going to do that.The YARD Stick One i mentioned before could probably do it.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: May 08, 2019, 09:09:07 am
content: Get a small diode like 1N4148, connect a scope probe ( or input of an audio amp) across it at the diode body, and keep the original lead length on the diode, sticking out either end.Holding this near the remote should pick up a demodulated signal.Look up "RF Detector" for more ideas.

author: Chriss
author_rank: Frequent Contributor
timestamp: May 08, 2019, 07:44:30 pm
content: You mean I should do something like this on the picture?I never played with RF stuff because I didn't liked it, but now I'm really curious about this field of electronic.This video looks also interesting for me:Is this any good for my project or maybe to learn?

author: shadow.dark
author_rank: Contributor
timestamp: May 09, 2019, 07:00:09 am
content: Quote from: Chriss on May 08, 2019, 07:44:30 pmdo NOT hook on the glass body of the diode, hooks（probe）on one lead of the diode, alligator clip（GND） on the other lead.