[dazq]

Long time no update , but due to uncovering some info I made HUGE progress on this!!!!

So , the data coming from the head unit out to the external "can" box IS serial! Actually 38400 8n1 to be precise

6bytes of data
Header
Function id
Payload length (always 2)
Padding1
The data
CRC

The CRC is 255 - sum of bytes 2-5

All in this means I can read and decode the button pushes eg on the HVAC /AC panel seen above.


The header byte value varies according to what OEM and model you have selected. Eg GM seems to use Dec 46 (hex 2e) for all models on my unit.

I have found some func codes , which also vary according to oem (doh!)

This Info is for the "raise" can box option.

More soon

[dazq]

I set my head unit to ford ( focus ,fiesta) to see how it varies to GM.
It does still use 46 as the header but the length is also longer for some function.
So
Up to 12 bytes of data
Header ( still 46 Dec)
Function id
Payload length (up to 8 !)
Data 1
::. ( Number of data according to payload)
Data 8
CRC

The CRC is 255 - sum of bytes 2+3 and all the data bytes .
An overflow can occur as it is only a byte value. This is correct the CRC does calculate ok with a byte variable.

I have some testing reader code I am running on an esp32 which I will be putting up on GitHub . It's pretty simple just building the data packet together but may be of help to someone.
More soon

[danielverdin]

super interested in this project! it looks like you might have the ability to build an entirely digitally controlled HVAC with your head unit!! hope to see more! great job so far.

[dazq]

super interested in this project! it looks like you might have the ability to build an entirely digitally controlled HVAC with your head unit!! hope to see more! great job so far.

Thanks , yes that is the plan thus deleting the need for other controls for the HVAC.
I am still working on sending data to the head unit but I think I am getting there