Analog sensor used by two boards with different voltage levels

Archive
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I’ve got a scope at work, just not qualified to make a good use out of it :smiley: I’ll ask guys at work to do their magic and analyse this display connection. If this fails the only option left will be the analog magic

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The battle was long and took 5 hours and a few coups of coffee… but I made it! Indeed the scope saved me at least an hour or two :wink: I will describe the solution in details after i get some rest :wink: Meanwhile a proof:

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So reverse engineering was the key. This is the list of steps i made to get the temperature readings from this system:

  1. Used a scope to see the signal format on the wire between main unit and display. It uses only one wire and bi-directional communication is needed so there had to be some request-response commands. And indeed, most of the time the signal was high but each second it droped to 0 for about 8 ms, after that a series of high-low, then another 8 ms low and another series of high-low. This fitted into the request-response thesis. After some drawing i came up with the signal format as shown in the picture.

  2. I plugged in a Domino and used the InputCapture class to get the signal and decode it. After some tests i finaly got the hex format of those 11 data bytes. The display is sending three types of commands:

AA3C0804000000000E02A7
B00E3C788A285014008C9B
C06408011428011E0A82AB

  1. I figured out that the last byte is a simple XOR CRC, the first byte is the command type. The only thing that was changing in display commands were three last bytes before CRC. Those are the DD, HH, MM :slight_smile:

  2. For each command the main unit sends a response with the same command type but different body. I needed to change the resistance on temperature sensors pins so that the main unit sends different data. This way i figured out in which bytes contain the temperature reading. The value is already in Celcius format so i don’t have to do any conversion!

Reverse engineering is fun!

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Oh you are sniffing the LCD now. Great!

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Thank you for all help with this project. Here is the result. Online temperature readings of a solar heating system monitored by .net micro framework device.

[url]http://www.sunportal.pl/technologie/wykres/?year=2011&month=5&days=19[/url]

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Congratulations !!! Great work :clap: