Need some help to view data without the rf noise in the way - Page 1
Forum section: electronics / beginners

author: A-day
author_rank: Newbie
timestamp: January 01, 2017, 12:21:40 am
content: Hi all,i'm new here ! and i'm also a weekend hack with zero schooling on electronics with that said ill try to understand whatever help i can get.i have a 125khz module from a car alarm that i would like to re-use on a future project but first i need to understand how it works and how to decode the data on the output. the problem is when i press a button i do see the data being output from the module but it's so much rf noise coming in that it's hard for me to clean it up on the scope to view the data. i'm stuck at work for the next 5 hours but i did bring a hack pack in case i had time to do some tinkering

author: ataradov
author_rank: Super Contributor
timestamp: January 01, 2017, 01:12:12 am
content: Can you show some scope traces? What makes you think it is RF noise? How exactly do you probe your signals?

author: A-day
author_rank: Newbie
timestamp: January 01, 2017, 01:54:30 am
content: well its just a shot in the dark but it seems to pick up anything on the band but ive connected it according to the labels

author: ataradov
author_rank: Super Contributor
timestamp: January 01, 2017, 02:04:11 am
content: This picture shows absolutely nothing of any use. All those modules are exactly the same, so picture of the module does not say anything.Show your overall setup and scope traces you see and think are wrong.

author: A-day
author_rank: Newbie
timestamp: January 01, 2017, 02:05:18 am
content: i have tried this on real scopes at home this is my hack pak gear so please don't judge me i have a gear addiction with little money to get my fix.

author: A-day
author_rank: Newbie
timestamp: January 01, 2017, 02:11:28 am
content: i'm learning photo post size limits. this is my first time using this scope for the task my rigol picks up a ton of garbage but this isn't doing too bad im emailing pics from phone to laptop so it's a small delay between post

author: ataradov
author_rank: Super Contributor
timestamp: January 01, 2017, 02:12:10 am
content: So where is RF interference mentioned in the first post? I'm not going to pull information from you, if you need help, then give info.

author: A-day
author_rank: Newbie
timestamp: January 01, 2017, 02:26:30 am
content: i'm not getting the same garbage on this scope as my rigol im sure it could be the settings but i need to be able to view the data on my bench so i can use the software decode to properly identify the buttons to re-purpose the module ill put this off till i get home and connect to a proper scope then i can show the exact problem, i just figured it would be the same on the pocket scope

author: tautech
author_rank: Super Contributor
timestamp: January 01, 2017, 02:27:41 am
content: Quote from: A-day on January 01, 2017, 12:21:40 amThat probably uses ASK or FSK keying from an encoder along with an address bit/s.If you're lucky it won't have a rolling code but if it does you'll be SOL to repurpose it.To "see" what it's doing you need to disable the RF and probe the output of the encoder chip.Easier still, get a pair of RF modules from these guys, direct or from their eBay shop:http://www.rfremotech.com/Others.html

author: A-day
author_rank: Newbie
timestamp: January 01, 2017, 02:40:40 am
content: i would have never thought to do things that way and it does make since. i haven't read the data sheet to know how and if it has rolling coding thanks for the insite

author: KludgeIt
author_rank: Contributor
timestamp: January 01, 2017, 02:46:08 am
content: I bought some of those modules, they sell them on aliexpress.com, for cheap!First, I made the mistake of buying the 315Mhz modules, xmitter - rcvr, and every garage door control, baby cam/monitor, ham, car fob, etc., was tearing me up. I was using them to communicate between arduino avrs, and for temp, wind speed, humidity ...Finally, I bought a handful of the 433Mhz modules, and all worked perfectly ... that isn't 315Mhz, is it?Go to aliexpress.com, and search with "315mhz 433mhz transmitter receiver module", you will be able to see what I am speaking of ...

author: jwm_
author_rank: Frequent Contributor
timestamp: January 01, 2017, 02:52:15 am
content: Are you sure it is actual noise? Good digital scopes can appear noisy when things are not properly connected.https://www.eevblog.com/2014/04/10/eevblog-601-why-digital-oscilloscopes-appear-noisy/

author: KludgeIt
author_rank: Contributor
timestamp: January 01, 2017, 02:57:56 am
content: If you write in C, C++, take a look at the arduino libraries, or just use them, they should provide you with examples of decoding the FSK modulation, etc. ... I forget what the libraries are named, but a lttle research or quesions on the arduino forums, where they use those things all day long, should speed you up A LOT.I went to the local walmart superstore, and recorded the codes to lock/unlock cars, open trunks, set off their alarms, etc ... all with an arduino nano and one of those modules set for 315Mhz ... I NEVER USE MY CAR FOB IF ANYONE IS WITHIN A MILE OF ME, ANYMORE ... IT WAS A GREAT EDUCATION OF HOW DANGEROUS THOSE CAR FOBS ARE!... point being, even if it won't work out in the location you have planned, you can take it where there are a lot of cars, and have some fun ...

author: A-day
author_rank: Newbie
timestamp: January 01, 2017, 03:46:52 am
content: No it's 125 i think i buy so much cheap and chearful crap from china it should be no problem to find the 433's to be honest my first choice was a zigbee but then i'd have to make a transmitter and i just wanted a solid reliable remote/fob i didn't think about how much traffic that i would encounter. as for writing code i haven't found anything that i wanted to do to inspire me to learn. i've replaced chips on quadcopter boards flashed new firmware but never have i written a single stitch of code and that why i'm looking to do a project that will push me to learn. i repair lots of stuff but creation is a different Beast !

author: tautech
author_rank: Super Contributor
timestamp: January 01, 2017, 04:05:25 am
content: Quote from: A-day on January 01, 2017, 03:46:52 amYou need to check your local regulations as to the frequency you're allowed to use for Telemetry. AFAIK the US is 315 MHz and NZ and AUS is 433 MHz.I've got a # of RFremotetech transmitters and receivers and the frequency that gives the best long range performance are 315 MHz. For instance a TCW Series keyfob transmitter that I use almost daily gives me control of a water pump @ 500 meters whereas they're only rated to 200 m.

author: KludgeIt
author_rank: Contributor
timestamp: January 01, 2017, 04:08:21 am
content: I just used the libraries in the code, and never looked at the code in the libaries closely, BUT, are you sure the 125Khz isn't just the "baud speed", and "FSK data rate" of the modulation of the actual 315/433Mhz modules ... I mean, I don't know, I just wanted to make some outside weather stations, better than I could buy, and last MORE THAN A YEAR ... the ones I built are still in operation, over two years later, point being, they seem to work well.... anyway, that is all my knowledge on them, and you probably know a lot more than me, and I freely admit that ... good luck ... but still, try the arduino forums, they explained the FSK modulation to me, and got me up to speed quickly ... a couple of years ago they were a lot of people experimenting with those ...

author: KludgeIt
author_rank: Contributor
timestamp: January 01, 2017, 04:20:57 am
content: Well, one more time ... my son just pointed out that the 868Mhz go a lot further, and seem to have a lot less "noise" ... I think i will grab a couple and upgrade my 433Mhz moduleshttps://www.aliexpress.com/item/10-pcs-868MHz-SI4432-Module-Remote-Wireless-Module-Wireless-Transmitter-Module-Wireless-Communications/32445795845.html?spm=2114.01010208.3.2.D8NmnD&ws_ab_test=searchweb0_0,searchweb201602_0_10065_10068_10000009_10084_10083_10080_10082_10081_10060_10062_10056_10055_10054_10059_10099_10078_10079_426_10103_10073_10102_10096_10052_10050_10107_10051_10106,searchweb201603_0,afswitch_2&btsid=3ef7e8d3-fbf5-4e42-b0a8-22ca2484b375WOW, that seems a long address! ... and seemed so short when I cut it to paste! just search for the 868Mhz modules on aliexpress, son says they have them at 929Mhz too, but cost more ...

author: ataradov
author_rank: Super Contributor
timestamp: January 01, 2017, 04:28:22 am
content: I concur with others, 125 kHz is a typical maximum frequency before modulation. Actual baudrate can be anything below this nunber, and there is no standard, those modules just pass though stuff from one end to the other.

author: eKretz
author_rank: Frequent Contributor
timestamp: January 01, 2017, 04:29:47 am
content: Just to make sure - the wire with the ground clamped is stripped, right? Not just clamped on the insulation? Something that might cause interference could be environmental as well - your Rigol at home is probably higher bandwidth and more sensitive to interference too.There could also be something it's picking up at your home that just isn't there at your work. For the longest time my GF couldn't figure out why her Wi-Fi died every time she was cooking dinner - until I came over once and saw that she was standing right next to the microwave with it running every time her Wi-Fi stopped working.

author: ataradov
author_rank: Super Contributor
timestamp: January 01, 2017, 04:31:21 am
content: Quote from: eKretz on January 01, 2017, 04:29:47 amNoticed that as well, but pictures don't clearly show this part and I was going to bring this up after we see some traces of the "noise".

author: tautech
author_rank: Super Contributor
timestamp: January 01, 2017, 07:25:32 am
content: Quote from: KludgeIt on January 01, 2017, 02:46:08 amNo, different seller.RFRemotech used to have a much larger selection than they have now in their eBay store, but some of the good basic modules are still there:http://stores.ebay.com/RFRemotech?_rdc=1Their Magic Receivers are quite neat and can be configured to Momentary, Toggle, Latch On and Latch Off outputs and can also support activation from a # of transmitters, and from the transmitters from all of their range.Email them direct for pricing, datasheets, installation instructions, and product recommendations to match your needs, they're a pretty helpful bunch.Remember to tell them the frequency you require and that should match your country's free telemetry band for your installation to be legal.http://www.rfremotech.com/