Vaillant Ebus - tapping into data

[Harry Bloomfield]

I have spotted a circuit which translates Ebus data to USB, this one http://ebus-wiki.org/lib/exe/fetch.p...rduinoebus.pdf

Which uses an Arduino plus an FTDI to interface the Arduino to USB and thus to a PC. I have tracked down an Arduino PCB which includes the FTDI on one PCB, but I have zero experience of Arduino. (eBay item number: 173727139497)

Anyone know if the combined PCB would work and would it also work with Vaillant's Vrdialog software to connect to my system please - Vaillant Ecofit pure 418, VR65, VRC 470F ??

 

[MeldrewsMate]

It seems that the only processing that the Arduino/FTDI will do is produce a series of ones and zeros to correspond with those produced by the Ebus. The software to convert the data stream to something meaningful is missing, though probably easily obtained if you have the Ebus protocol.
I can't help you further, perhaps others can.

 

[endecotp]

You could replace that arduino with a handful of transistors and resistors.

 

[Gasguru]

Ebus is a lot more complex than you might think....

That diagram is just a very simplistic layout...not a real interface.

Just to give an idea of the data structure... http://www.pittnerovi.com/jiri/hobby/electronics/ebus/Vaillant_ebus.pdf

and a typical isolated interface on page 25... http://ebus-wiki.org/lib/exe/fetch.php/ebus/spec_prot_12_v1_3_1_e.pdf

 

[Dan Robinson]

Ebus is a lot more complex than you might think....

That diagram is just a very simplistic layout...not a real interface.

Just to give an idea of the data structure... http://www.pittnerovi.com/jiri/hobby/electronics/ebus/Vaillant_ebus.pdf

and a typical isolated interface on page 25... http://ebus-wiki.org/lib/exe/fetch.php/ebus/spec_prot_12_v1_3_1_e.pdf

Will have a compare and contrast session with the OpenTherm protocol later.

 

[endecotp]

The important bit is that, quoting page 4 of your second PDF, it is ”realised using a standard UART”. So it should be possible to build a bus monitor (but perhaps not an active participant?) as proposed by Harry, using a USB-to-Serial device. The most difficult part is the level conversion; for a bus monitor you need something like the top half of the circuit on page 23, which uses an op-amp; that could be reduced to just transistors if you wanted.

 

[bernardgreen]

The important bit is that

The monitoring tap should be opto-isolated from the E-bus to prevent the 0 volt of the monitoring system's power supply from affecting the E-Bus.

Some E-bus systems ignore polarity ( a bridge rectifier between E-Bus and the circuitry "solves" this infrigment of the original specification )

 

[Harry Bloomfield]

The monitoring tap should be opto-isolated from the E-bus to prevent the 0 volt of the monitoring system's power supply from affecting the E-Bus.

Some E-bus systems ignore polarity ( a bridge rectifier between E-Bus and the circuitry "solves" this infrigment of the original specification )

I think that the worst that could happen with a none isolated monitoring tap, is the Ebus being pulled to ground via the interface. The Ebus will be quite well protected against such as this, because the system will be designed to be installed by plumbers - so it will just stop communicating until the ground fault is removed.

The Arduino arrived this morning, but I am not rushing into this - there is no urgency, it is just a project first and foremost to satisfy my natural curiosity..

 

[bernardgreen]

the system will be designed to be installed by plumbers

Hence the removal of the need to observe polarity in some boiler / heating systems ? ?.

so it will just stop communicating until the ground fault is removed.

Loss of communication could create a hazard if the system is not designed / programmed to fail safe in the event of an un-expected loss of communication.

 

[picasso]

didn't realise already posted.

 

[endecotp]

I think that the worst that could happen with a none isolated monitoring tap

I don’t know what your plan is here. If I were building a product, it would certainly be opto-isolated. If I were doing something “for fun”, I’d probably run it on a laptop or use some similar approach to get an isolated power supply and not worry about the extra complexity of isolation.

I’d also look at the signals with a ‘scope, and if there is interference (e.g. at switch-mode power supply frequencies!) then I’d add isolation.

The thing you originally posted, and linked again by picasso, using software on the Arduino to covert the voltage levels, is ghastly; please don’t use that.

 

[Gasguru]

The issue is whether the bus lines are referenced to true earth...boiler manufacturers almost randomly tie their DC grounds to Earth, I've found there is no consistentcy.
A differential scope probe would be the first step...before damage is done.

 

[picasso]

The thing you originally posted, and linked again by picasso, using software on the Arduino to covert the voltage levels, is ghastly; please don’t use that.

Sorry what do you mean "using software on the Arduino to convert the voltage levels" as far as I can see the resistors are dropping the voltage and the Arduino is just processing the signals or have I misunderstood?

 

[Gasguru]

I predict smoke and cooked laptops....

 

[picasso]

Hows that?