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NJSS
Member Since: 06 May 2009
Location: Catherington, Hampshire.
Posts: 10808
  
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I like the look of the Hornet remote control - and would appreciate user experience, plus what kit to buy & how to install it.
Nigel Am I Gammon or Woke ? - I neither know nor care.
2016 Discovery 4 Landmark
2011 Mercedes Benz SL350 (R230)
1973 MG B GT V8 - 3.9L John Eales engine, 5 speed R380 gearbox, since 1975.
1959 MGA roadster - 1.9L Peter Burgess Engine - 5 speed gearbox
Past LRs - Multiple FFRs, Discos & a Series I - some petrol, some diesel,
none Electric or H2 fuel cell - yet.
There are 10 types of people in this world: Those who understand binary, and those who don’t.
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 11th Dec 2009 9:54 am |
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stapldm
Member Since: 11 Sep 2006
Location: Swine Town
Posts: 2330
 
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Iain G wrote:I took a trace of the W-bus serial data using a storage oscilloscope if any electronics wizz kid wants to make their own (I was going to program a PIC IC to give the o/p). It seems the W-bus comms is one way only and contains a hell of a lot of bits on a 4us clock frequency.
Iain, as the timer flame icon is turned off by the FBH when it shuts down (as per when the car wakes up) there must be some kind of bi-directional data involved too. Not that I have anything in mind for it, but I'd appreciate a look at the data trace of the w-bus signal, just for interest (how nerdy is that!). Dr. Ian Malcolm:
"Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should."
Transgenic tomato anyone?
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| 11th Dec 2009 5:49 pm |
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Iain G
Member Since: 31 Jan 2009
Location: Filey
Posts: 430
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Stapldm.
You are probably correct about the Webasto giving a signal out if it turns the 'flame' signal off on the timer upon vehicle wake-up. This is something I didn't check for, but I suppose if you were making your own timer I can't really see the advantage of the function.
The W-bus is normally at 10V, held their via a resistor to a 10V rail. This signal is pulled down to 0V by whatever device is comunicating. The waveform traces I took were of the Webasto 1533 timer output, without been connected to the FBH. I wasn't able to print the signal off but I wrote out the trace.
When the timer output goes on, the serial data is as follows (CAUTION - Geek speak ahead):
(starts from hi - '1') 00010110011011000000010100001000100111100001000010000 (ends hi - '1') Total length of transmission 22.2ms.
When turning off, the data is:
(starts from hi - '1') 0001011001100100000011000001000011001100100 (ends hi - '1'). Total length of transmission 17.6mS.
The 1's and 0's represent 10V and 0V respectively. The duration of each bit is 0.42mS. I ran each trace three times to verify my results and can confirm any high / low duration were divisible by 0.42mS
Looking at the data the only bit of sense I can make out is highlighted in red. This looks like it could be calling an address and the last 2 bits indicate whether the heater should turn on or off, though this is only speculation. This string of data is followed by a pause which on first inspection looks like it is waiting for a response. To identify wether this was the case or not I hooked it up to the webasto, but as I didn't want to appear a fruit cake carrying my oscilloscope outside and laying it on the bonnet I elected to make up a simple circuit that should only allow data one way, namely a diode and a pull-up resistor on the FBH side. This still fired up the FBH proving return data from the FBH is not required.
Hope someone can take this the next step and start producing the W-bus signals reqiured. I'm sure there must be a demand for it as the 1533 sells for around £55 and is a piece of junk in terms of its timer capabilities, I bet most end users end up soldering wires across the start button to allow a better system to do the timing functions.
Iain
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| 11th Dec 2009 7:38 pm |
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