giofranco / webasto

Arduino project to control webasto heater via W-bus

Interfacing a webasto heater using K-line interface

Mostly because my webasto air top evo 40 broke down and I was told to send the unit back to repair shop for SW reset in order to get it working again. I decided to put some effort into understanding and hopefully be able to controll the heater without sending things back to repair shop in the future.

The goal of this project is the following:

1. Implement HW interface that can talk to the webasto implemented W-bus (K-line) using arduino HW and simple HW TTL/K-line interface. (DONE)
2. Implement SW that can sniff the webasto traffic. (DONE)
3. Implement SW that can talk to the webasto (IN PROGRESS)
4. Map protocol used to communicate with my webasto air top evo 40. May be scalable to other versions?? Already present in libwbus project. Already done in libWbus, just implement and check data (NOT NEEDED)
5. Build diagnostic box with status LCD display that monitors the Webasto heater. (NOT STARTED)
6. Build interface to pi and "big" LCD display together with HW enclosure to put in boat cabin so that WTT status information can be viewed "live" (NOT STARTED)

The arduino MEGA2560 was selected together with a raspberry pi (for remote development) was selected in this project.

Dependencies

*) Arduino framework

*) Arduino Makefile (Do not need IDE) https://github.com/sudar/Arduino-Makefile

*) newLiquidCrystal (https://bitbucket.org/fmalpartida/new-liquidcrystal/wiki/Home)

*) LibWbus (uses documentation only + code review) https://sourceforge.net/projects/libwbus/

W-bus protocol

The W-bus protocol is a bi-directional link using single physical line for communication. On the physical layer it uses 0 -> 12V signaling. The w-bus is a K-line interface. The K-line interface is described in ISO 9141. Normally the K-line is interfaced using integrated chips. In this project the TTL to K-line is solved using simple NPN PNP transistors.

On the physical layer the communication is a serial line with 2400 baud 8E1 format (NOTE: Arduino SoftwareSerial does not support parity check!!, use CustomSoftwareSerial or something similar that support parity. In this project I use meg2560 with 4 physical uarts. The protocol is packet based with the following structure

Header-length-command-data-checksum.

More information on the protocol can be found in the repo in text file: webasto_wbus.txt (stolen from libwbus repo)

HW interface

THe HW interface is simulated using LTspice from linear tech, which is an excellent freeware implmentation of SPICE. The HW interface is a TTL to W-bus (K-line) converter using standard resistors and NPN transistors.

Dependent on the ODB circuit used and the webasto K-line interface the input/output resistances may need to be scaled. The above circuit was simulated. The resulting curves with TX TTL baudrate 9600 shown at the W-bus output (12V) and the resulting curve at the RX TTL interface (+5v).

Webasto <-> PC arduino sniffer

Using arduino and together with a the RX parts of the above HW interface a sniffer was built and connected just to listen to the traffic between the Webasto air top evo 40 and the WTT software. The PC is connected viw ODB II inteface (RS232 + LM339 comp + misc passive) to the K-line at the smartcontrol/multicontrol of the webasto heater. Picture below shows the setup.

Below is the first packets sniffed from arduino side:

F43ACA6F5 F41F5060A365020A030615C1C7B42CD062871F244E4AA68C599133CD9E52575FF04AFF

Interpreted using libwbus documentation:

Line 1: Header = 0xF4, Length = 0x03 bytes, Command = 0xAC, Data = A6, Checksum = 0xF5

testing checksum (https://www.scadacore.com/tools/programming-calculators/online-checksum-calculator/)

The problem with the above was that the checksum did not fit XOR as from the documentation for LIBWBUS. After some reading it was discovered that the communication is on the physical layer serial-8E1 and the SoftwareSerial library does not support parity check. After replacing the SoftwareSerial with CustomSoftwareSerial that supports parity the following was sniffed:

F4 3 56 1 A0
F4 1F 50 30 1 3 5 6 7 8 A C E F 10 11 13 1E 1F 24 27 29 2A 2C 2D 32 34 3D 52 57 5F 78 89

Using XOR parity the last byt checks out. According to the libwbus documentation the two commands above are 56 and 50. It was noted in this phase that the RX response was missing. This was fixed using a modified HW interface. HW schematic above is updated. Needed PNP switch instead of NPN switch on RX input.

After this fix the following was sniffed

TX-cmd:F4 03 56 01 A0 RX-response:4F 10 D6 01 04 02 01 07 07 01 00 A3 01 00 97 01 01 BB

This concludes that the sniffer part now works. The webasto sniffer is copied to the webasto_sniffer repo. Just to keep this strand alone

To do loopback tests and also check that you send the correct packets to the wbus the arduino uno that was first used was swapped to an arduino mega with 4 physical uarts. It is possible to solve it with arduino UNO and but to save time the uno was skipped.

SW to control webasto

First test was to send some init commands to get the webasto up and running

F4 03 51 0A AC
4F 04 D1 0A 41 D1
F4 03 45 31 83
4F 0D C5 31 01 02 02 05 03 07 05 0A 0A 0A B9
F4 03 51 31 97
4F 16 D1 31 01 02 03 04 06 07 08 09 0B 0C 0D 0E 0F 10 12 15 18 19 1A BA
F4 03 51 0C AA
4F 0A D1 0C DA 5D F8 DA 39 00 04 00
F4 02 38 CE
4F 0B B8 0A 00 00 02 BE 02 BF 04 00 F3
F4 03 53 02 A6 4F 11 D3 02 29 04 23 28 2C EC 14 3E 80 32 C8 3E 80 06 81 F4 03 57 01 A1 4F 06 D7 01 81 72 8D E1

above is last init string Below is first status command

F4 03 56 01 A0 4F 10 D6 01 04 02 01 07 07 01 00 A3 01 00 97 01 01 BB

We have reached the WBUS_OK state We have reached the WBUS_OK state

The above shows that everything is working as expected. Now it is time to build the message parser.