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A friend of mine has the following puzzle(original post link: https://www.geocaching.com/geocache/GC46JBF_whats-changing) which we can't figure out how to solve:

ADEFBCDGBCDGABC
DGABCDADEFGDEFA
BCBCAEFGCDEADEF
ABDFGACFGACFGAD
EFACDEFCFGADEAC
DEGBFADEFGBCG A
DEGACDEFBCEFABC
DFGCADEFGACDEG.

Hint 1)

The first hint is the title "What's changing"

Hint 2)

The second hint is "7-segment".

Hint 3)

Using the the 7-segment system, the first character apparently is "C"(using ADEF). We can't however get the following characters due to not correctly applying the title hint.

Hint 4)

This is a geocaching puzzle of which the result should be something like this: N51° 11.542 E 004° 23.867

Can anyone help us solve this puzzle?

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  • $\begingroup$ It's actually pretty simple to solve. $\endgroup$ Commented Apr 16 at 13:35
  • $\begingroup$ Just feed it through a 7 digit cipher decoder was what I was thinking $\endgroup$
    – PDT
    Commented Apr 16 at 13:36
  • $\begingroup$ @pdt Have you looked at the hints? I don't think this will be found in an online decoding tool. $\endgroup$ Commented Apr 16 at 13:53
  • 1
    $\begingroup$ dcode.fr/7-segment-display? Is this not correct $\endgroup$
    – PDT
    Commented Apr 16 at 14:06
  • 2
    $\begingroup$ @PDT It doesn't quite do this code (see hint 1). It should decode to "CACHE LOC=" etc. $\endgroup$ Commented Apr 16 at 14:07

1 Answer 1

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First split the encoded text into blocks of letters that are in alphabetical order.

ADEF BCDG BCDG ABCDG ABCD ADEFG DEF ABC BC AEFG CDE ADEF ABDFG ACFG ACFG ADEF ACDEF CFG ADE ACDEG BF ADEFG BCG ADEG ACDEF BCEF ABCDFG C ADEFG ACDEG.

The letters represent the

segments in a 7-segment display. They are labelled in this order:

   -A-
 F|   |B
  |-G-|
 E|   |C
   -D-

Next apply the hint from the title to figure out how to decode this.

The blocks of letters represent those segments that are changed when the display goes from one character to the next. The display starts off showing nothing, so when segments ADEF are changed you see the letter C. If the next block of segments, BCDG is changed, that means BCG are switched on and D is switched off, then the result is ABCEFG, which represents the letter A.

This results in the following:

First column is the code, second column the current state of the display, and the last column the symbol shown on the display.

 ADEF   ADEF    C
 BCDG   ABCEFG  A
 BCDG   ADEF    C
 ABCDG  BCEFG   H
 ABCD   ADEFG   E
 ADEFG  -
 DEF    DEF     L
 ABC    ABCDEF  O
 BC     ADEF    C
 AEFG   DG      =
 CDE    CEG     n
 ADEF   ACDFG   5
 ABDFG  BC      1
 ACFG   ABFG    degrees
 ACFG   BC      1
 ADEF   ABCDEF  0
 ACDEF  B       '
 CFG    BCFG    4
 ADE    ABCDEFG 8
 ACDEG  BF      "
 BF     -
 ADEFG  ADEFG   E
 BCG    ABCDEF  0
 ADEG   BCFG    4
 ACDEF  ABDEG   2
 BCEF   ACDFG   5
 ABCDFG B       '
 C      BC      1
 ADEFG  ABCDEFG 8
 ACDEG  BF      "

So the decrypted text is:

CACHE LOC=n51o10'48" E0425'18"
Note that the degree symbol is missing after E04, but that can be remedied by splitting the subsequent ACDEF block into AC DEF, to give the final answer:
CACHE LOC=n51o10'48" E04o25'18"

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