Which IR protocol is this? - Page 1
Forum section: electronics / projects

author: DaGlitch
author_rank: Contributor
timestamp: May 24, 2015, 02:22:33 am
content: Been trying to figure this one out. I'm looking at a simple IR transponder unit. The image below is the raw IR coming from it. It had the number "3420" written on it, so I know that will correlate to somewhere in the data. My guess is that it's 20 bits possibly? Carrier frequency looks to be ~ 460kHz. The numbers I have written above each chunk is the pulse count which might be +/- 1. Then time in between each pulse. The 2nd image is how I imagine the way each bit is broken up (which may be incorrect).

author: bson
author_rank: Unknown
timestamp: May 24, 2015, 05:12:34 am
content: Looks bi-phase encoded. RC-5 perhaps?3420 is hex d5c, or binary:1101 0101 1100Your pulse train (mark = 0, space = 1) divided into ~20usec clock periods0,1,0,1,1,0,0,0,0,1,0,0,0,1,1,1,0,1,0,1,0,1,0,0,0,0,0,1,1,0,1,0,1,0,0,1,1,0Bi-phase decoded (transition during clock = 1, no transition = 0):1 1 1 0 1 0 1 0 1 1 1 0 0 1 1 1 1 1 1^^^^^^^^^^^^^^^^^^^^^^^^^^^^There you go.http://ckp.made-it.com/encodingschemes.html

author: DaGlitch
author_rank: Contributor
timestamp: May 24, 2015, 05:41:46 am
content: Thanks for the response,I guess the only difference I have in what you have for the pulse train is the 1 I have indicated:0,1,0,1,1,0,0,0,0,1,0,0,0,1,1,1,0,1,0,1,0,1,0,0,0,1,0,0,1,1,0,1,0,1,0,0,1,1,0,1^But maybe I'm just not getting the decoding part as I came up with:1 1 1 0 1 0 1 0 1 1 1 0 1 0 0 1 1 0 0 1^^^^^ ^^^^^ ^^^^^D 5 D?

author: DaGlitch
author_rank: Contributor
timestamp: May 24, 2015, 06:38:21 pm
content: Any other ideas?

author: Dave Turner
author_rank: Frequent Contributor
timestamp: May 24, 2015, 08:13:32 pm
content: Have a look at the IR decoders available for the arduino. There's some useful info there that might help.

author: JoeO
author_rank: Frequent Contributor
timestamp: May 25, 2015, 01:31:34 pm
content: It might help if you supplied more information. What is it? Who is the manuf.? Picture.

author: bson
author_rank: Unknown
timestamp: May 25, 2015, 07:22:35 pm
content: To decode bi-phase, make sure you sample the levels correctly at the recovered clock.

author: jimmc
author_rank: Frequent Contributor
timestamp: May 25, 2015, 08:37:11 pm
content: Dug this out of my bookmarks, might be of interest (I haven't tried it myself) ...http://wiki.nethome.nu/doku.php/analyzer/startJim

author: DaGlitch
author_rank: Contributor
timestamp: May 26, 2015, 04:46:51 am
content: It's essentially this. it's an ir transponder.Quote from: JoeO on May 25, 2015, 01:31:34 pm

author: macboy
author_rank: Super Contributor
timestamp: May 27, 2015, 02:23:55 pm
content: To me, it looks like it could be UART (async serial) data at 38400 using OOK (on-off keying) with "on" (carrier present) being Low or zero and "off" (no carrier) being a High or one. With TTL level UART, idle is High state and the start bit is a Low, and stop bit is a High. Data bits are non-inverted (Low=0).I say that it might be serial data because there is a start bit (on) followed by 8 various bits, followed by a stop bit (off), and this is repeated 4 times (40 bits total with 32 data bits), without framing errors, i.e. the start and stop bits always fall in the right place. And a ~26 us bit period is very close to 38400 baud, which is a very common baud rate.Assuming carrier present is "0" and idle is "1", then the bit sequence might be:0101100001000111010101000100110101001101(11111....)If you group the bits into UART-style framing with a "0" start bit, eight data bits, and a "1" stop bit, then you see that you have:0 10110000 10 00111010 10 10001001 10 10100110 1... followed by idle, a valid state.UART data is sent LSb first, so reverse the bits in each byte and the data becomes:b00001101 = 0x0Db01011100 = 0x5Cb10010001 = 0x91b01100101 = 0x65Notice that 0x0D5C is decimal3420. It seems to me this is probably your answer!(double check bits sequence and hex conversions)p.s. 455 kHz is a common IR modulation frequency, and you can buy nice little receiver/demodulators for that frequency. If you plan to receive the data from the transponder, then use one. It will be far less sensitive to noise and more reliable than anything you could make yourself.