How to read voltage and temperature from Chroma29

[probonopd]

According to

E-Paper_Pricetags/Custom_PriceTag_AccesPoint/CMDs explanation.txt

Lines 129 to 132 in caaacc2

	CMD 0x85
	Length 5 bytes
	0x0A83 = 2.691V
	0x0113 = 27,5°C

the answer to command 85 contains the voltage and temperature.

Sending command 05 or 85 (= 05+80) makes the whole display black. And we see something like this:

last answer: Msg from display NetID: 1 freq: 0 display: 0 8044533 = 85:05:71:0B:EC:00:01:00:00:00

How to interpret the answer?

• 85: The command that this is the answer to (= 05+80, 80 is added when the command results in data being sent back)
• 05: Length of this answer is 5 bytes
• 71:0B: Hex 0x0B71 = Decimal 2929 = 2.929 Volts
• EC:00: Hex 0x00EC = Decimal 236 = 23.6 degrees Celsius
• 01: Unknown?

So, how can we get the values without making the display black?

According to the same page, command 02 should give us the voltage and command 19 should give us the temperature.

Just sending the command 02 results in

last answer: Msg from display NetID: 1 freq: 0 display: 0 8365754 = ���?

Why is there garbled output instead of the hex answer?

Can we/do we need to combine multiple commands, like sending command 0219 for getting both the voltage and the temperature? This gives

last answer: Msg from display NetID: 1 freq: 0 display: 0 9135793 = 82:02:F5:00:99:03:7A:0B:00:00

How to interpret the answer?

[atc1441]

Also after an image is send the temp and battery is send back just as info.

The garbage answer you got back at 02 is an error, it should return something like you got int the 0219 cmd. 82:02:F5:00

The 0219 cmd can be parsed the following:
82 = cmd 2 with incoming data
02 = 2bytes of data incoming
F5 = actual data byte 1
00 = actual data byte 2

so 0x00f5 = 24.5 degrees Celsius

99 = cmd 10 with incoming data
03 = 3bytes of data incoming
7A = actual data byte 1
0B = actual data byte 2
00 = actual data byte 3

0x0b7a = 2.938 Volts

00 = the length of replying data is always is a pack of 5bytes so this 00 is not used

as you can see multible cmds can be send at once, when sending an image update 3 cmds are send at once, header of img, actual img and the refresh cmd itself. the refresh cmd always return the temp and battery data in return

[probonopd]

Maybe we should parse that data and output it in clear text whenever we receive it?

[atc1441]

Yes.
A dynamic incoming cmd parser is still needed to be written, as also the display answers with multiböe cmds in one go, on display update you get answer 03 04 85 ...
But on resfresh only 85 ...

So that is needed to be parsed correctly, also the incoming ack needs to be looked at, as if a msg is send again it will currently be added to the answer buffer even if its the same as already received.

I did not do anything with the answer buffer for now as i concentrated on the system itself