Vbus connection to a built-in RS485 port

[Milkwood]

First: thanks to all in this group for providing all the info about Vbus.
I've looked through all the 100+ posts but I still have some questions about the physical connection to my computer.

I use a Nanosg20 mini-PC with Debian Linux to monitor my PV system en some weather stuff.
I would like to add my Resol Drainback DeDietrich (page 66 of Vbus spec) to this board.

Many of you use the Vbus to USB converter, and I know it might be easier to use this one but since my Nanos has a built-in RS485 port I would love to use it without the need to convert signals a couple of times.

From what I understand I cannot connect the Vbus directly to an RS485 port, is that correct?
Is that because of different voltage levels, and if so, does anyone have a schematic to hook the Resol up to this port?

BTW, I saw the circuits in the Vbus specs but I can't make any of those.

[Raphael Mack]

Hi,

This is interesting, I also have a NanosG20 connected to a Resol
controller. Anyhow I decided to go the easy way and buy a
Vbus/LAN-adapter - it is enough work to implement the SW on the Linux
side to decode the Vbus data stream, so I didn't want to have problems
with the hardware. The adapter is not low priced, but when taking into
account the cost of a nice housing and the time do assembly any kind of
self-made adapter it is worth the price in my eyes.

Regards,
Rapha

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[Milkwood]

Thanks Rapha,

That is excacly the consideration, I was hoping someone would have a nice little circuit with only a couple of parts to achieve this.
I've read some reports here using ordinary RS485 to RS232 converters that did work.

The thing is: I'm not even sure the Resol USB-adapter will work with the Resol Drainback system. It has 2 x 2 pins (9,10,11,12) labeled "Vbus" as pair, other Resol controllers only have 2 connections?

And besides the availability (It's hard to find them anywhwere, Resol does not sell directly) the price is steep, ebay lists it now for 81,50 euro..

Regards.

[Milkwood]

I made some progress. Be aware that I own a DeDitrich Drainback made by Resol, other models will behave differently.

I put an LED with a 10k resistor between Vbus- and Vbus+ and noticed one short burst of light and one longer within one second.
So even without querying the device, it spews out data every second. Is that the case with all models?

I decided to redraw the schematic in de Vbus spec (sheet 3/4 on page 6) to get a better understanding how conversion is done.
(redraw of circuit). Within the red elipse is the parasitic power supply. Within the green one is the actual conversion of levels, followed by an isolator.
It all starts with a bridge to convert the serial stream to a ground/5volt level.
On my oscilloscope, connected to the partial (quick and dirty) ciruit on a breadboard, the serial stream shows as sort of square wave, with not so steep slopes.

I connected the circuit to the Rx of my serial port on my Laptop et voilà:

AA 00 00 11 43 20 00 05 00 00 00 00 C0 00 00 06
AA 10 00 11 43 10 00 01 05 05 6F 01 30 01 0F 59 E0 BF 80 E0 C0 C0 00 00 00 80 CF E0 80 80

Starts with AA as it should, 11 43 is my model number (4311 on page 66) so that is correct. For the rest I'm stuck.
The first line has a short code with command 0050 to clear the line. The second presents data after the 16th byte.
But the hex values to decimals make no sense.
According to the Vbus specs there's a lot of byte/bit juggling after that, I don't understand the logic of it. If anybody has info on the software part I'd love to know.

I'm on Linux, Debian Squeeze, and would like to use Python as programming language but maybe there are already some working examples in C?

[Andrew White]

You can try this, it's what I use and you should be able to use for other models as everything's is passed as command line options

http://code.google.com/p/vbusdecode/

Sent from my iPhone

[Milkwood]

Thanks Andrew, I will look into it, Iwas just checking out the German "vbus-decoder".

I will compile your code after I finish the hardware interface, I still have some read errors, probably because I use regular diodes and a slow opto..