JP1 Remotes

yesok · Joined: 25 Aug 2006 Posts: 136

Hello Robman,

shineangelic · Joined: 08 Aug 2012 Posts: 2

This thread was somehow useful to start peeking into Samsung IR Codes. I'm generating IR codes for Samsung AirCon Model FBMH026FB with Arduino, so I had to decode and understand commands first.

The results of my work is located at:
https://docs.google.com/spreadsheet/ccc?key=0Aupzmp8AqC8JdGtNOXhUc0R0WC1hbVdRa0p3aDVxdFE#gid=0

it is a spreasheet with all dumped values and the interpretation of results. AFAIK, aircon unit sends out 2 or 3 "bursts" of 56bit data, depending on command. Each single burst is very similar to ones described on this old thread.

The problem I have is related to checksum.

Since I have to re-generate the IR codes wayback (not only storing them and resending them as they are) I do have to understand every single byte. I succesfully decoded all, but I can't figure out how to generate the 2bytes checksum.

Anyone figured out Samsung checksum algorithm?
Thank you

The Robman · Posted: Wed Aug 08, 2012 12:43 pm Post subject:

I have saved a copy of the file here, just in case the original disappears:
http://www.hifi-remote.com/forums/dload.php?action=file&file_id=11172
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The Robman · Posted: Wed Aug 08, 2012 10:19 pm Post subject:

I've got the first bit of the checksum, it's an XOR of the 6 nibbles in the 4th, 5th and 6th bytes.

The 4th bit is the complement of the first bit from 3rd byte.

Still working on the other 2 bits.
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vickyg2003 · Posted: Thu Aug 09, 2012 8:13 am Post subject:

Wow Rob, you are amazing.

The Robman · Posted: Sat Aug 11, 2012 2:33 pm Post subject:

Here's the spreadsheet where I've been trying to calculate the checksum:
http://www.hifi-remote.com/forums/dload.php?action=file&file_id=11192

The columns over to the right (AH thru AO) are where it happens. The 1c/2c/etc columns are the real checksum and the columns to the right are generated using code. If the result is correct, the font will stay black, if the result is wrong, the font will turn red. As you can see, the code for the 2nd and 3rd bits isn't correct yet, I'm posting this in case anyone else wants to take a stab at it.

Btw, I moved the Power Off code to the 2nd tab temporarily, as it's the only code where the 5th nibble (column W) isn't '8' (or '1000')
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Rob
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Please don't PM me with remote questions, post them in the forums so all the experts can help!

The Robman · Posted: Fri Aug 17, 2012 11:05 am Post subject:

It appears that this question has been asked in a few other forums:
http://stackoverflow.com/questions/11863920/samsung-ir-codes-checksum
http://arduino.cc/forum/index.php?topic=117746.0
https://plus.google.com/112370814111712506520/posts/9JKvkVBdBWC

I have confirmed the posted solution is correct, results here:
http://www.hifi-remote.com/forums/dload.php?action=file&file_id=11192

The checksum was originally cracked by "Ken Shirriff" but, so far, I have been unable to find his original post on the matter.
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Rob
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Please don't PM me with remote questions, post them in the forums so all the experts can help!

shineangelic · Joined: 08 Aug 2012 Posts: 2

Ok let me clarify this since I ended taking too many people's time.

I was really upset by that algorithm, having spent more than what was deserved to an air-conditioner checksum algorithm. So I started some discussions on related forums:

-Arduino, because Ken shirriff's library is based on that
-Stackoverflow, since it's a great place
-This forum, because the topic was strictly related to my issue

As for the third, I didn't believe I would had received an answer, 'cause last post was quite dated.

I's sorry I didn't notice the replies after second one, so I didn't notify of solution sent to me by epic Ken Shirriff some day ago.

The algorithm is as follow (credits to Ken):

1. Count the number of 1 bits in all the bytes except #2 (checksum)
2. Compute count mod 15. If the value is 0, use 15 instead.
3. Take the value from 2, flip the 4 bits, and reverse the 4 bits.
4. The checksum is Bn where n is the value from the previous step.

Note that step 2 is mod 15, not mod 16 (which you might expect). I
don't know why 15 is used as a special case instead of 0.

The implementation of this is still temporary and I can't post it. I'll come back when it's ready to be shown.

Thank you very much for your time and efforts.

The Robman · Posted: Fri Aug 17, 2012 9:37 pm Post subject:

Back to the original A/C learns (ie, the ones from 2007), I have updated the spreadsheet to reflect how the checksum is calculated:
http://www.hifi-remote.com/forums/dload.php?action=file&file_id=4390

For this one, you do the following:
1. sum the bits
2. do a MOD 16
3. subtract the result from 16
4. reverse the binary
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Rob
www.hifi-remote.com
Please don't PM me with remote questions, post them in the forums so all the experts can help!