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PostPosted: Mon Feb 04, 2013 5:09 pm 
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I believe that is the term normally used.

The concept is an alternative to running every single signal back to a centralised control through a large wiring loom. Instead you place a small interface module near each item or group of items which either produce a signal to monitor (e.g. fuel gauge) or control / drive (e.g. fuel pump, light bulb). The modules then link up via a common small cable, typically 3 or 4 cores, carrying signal and power. This drastically reduces the quantity of cable required and complexity, saving huge installation costs. It's something I have been doing for years in fixed installation round buildings etc, even using radio links for some agricultural applications to save miles of burried cable.

From what I can gather, systems currently available for automotive use are highly expensive. If this is the case then it's probably worth me having a further look at producing something more sensible. Probably the main market would be kitcars, maybe motorsports but most with enough money to rewire cars would probably go for proven makes anyway.

Any information that anyone can provide on what's available would be helpful, including suppliers, protocols, typical installations etc.

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PostPosted: Mon Feb 04, 2013 6:09 pm 
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Location: Aldershot,Hampshire
Car Model: ST205
The Motec PDM 15 im thinking of getting is £1300 - sure don will have some info

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PostPosted: Mon Feb 04, 2013 6:13 pm 
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Is that £1300 for just 1 module, of for a whole system for a car ?

I'm thinking in terms of £50 - £100 per module with maybe 6 inputs & 6 outputs.

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PostPosted: Mon Feb 04, 2013 6:18 pm 
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Location: Aldershot,Hampshire
Car Model: ST205
http://www.racedatasystems.co.uk/motec- ... odule.html

I was told thats what i would need for mine to get rid of all the under bonnet relays / fuses ect and remove lots of unnecessary wiring

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PostPosted: Mon Feb 04, 2013 6:29 pm 
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Ouch.

Not sure how 1 would reduce wiring, as it would all still need to wire back to the single unit. All it would do is remove the need for fuses.

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PostPosted: Mon Feb 04, 2013 6:45 pm 
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One of these (or similar) per output
http://uk.rs-online.com/web/p/mosfet-po ... s/0445412/

Plus processor, canbus interface, ancillaries - approx. £10 component cost.

Plus PCB

Plus box.

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PostPosted: Mon Feb 04, 2013 6:49 pm 
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Location: drinking devil fuel
Car Model: ST205
To reduce wiring you do need two minimum, 1 front and 1 rear
Their kit would be completely useless in the kit car scenario. It just replaces the 20 quid fusebox with a grands worth of kit. They have taken the modern concept of distributed control and implemented it in an archaic fashion. Yes it does have some benefit (staged shutdown etc) but it misses the point by a metric mile
If you look at a can based car most modules have local controllers. For all it's bells and whistles the bimmer wiring is very svelte

That's why I floated the idea .....


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PostPosted: Mon Feb 04, 2013 7:33 pm 
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Location: Aldershot,Hampshire
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Well if you can make me a system then id rather money go to you :)

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PostPosted: Mon Feb 11, 2013 7:18 pm 
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Blimey,
If you want to do it properly so you only have to run a 4 core cable round the car it don't arf add up quick :shock:
:shock: I've missed a few things off too :shock:

Doors could obviously be simplified but as is allows for fancy tricks like windows up when you lock :D :D

PDM1 - Front Of Car
Out 1 - N/S Flash
Out 2 - O/S Flash
Out 3 - Side
out 4 - Head
Out 5 - Main
Out 6 - Horn
Out 7 - Wash
Out 8 - Wipe
Out 9 - Driving Lights

PDM 2 - Cabin
IN 1 - Turn Left
IN 2 - Turn Right
IN 3 - Hazzard
In 4 - Horn
IN 5 - Side
IN 6 - Head
IN 7 - Main
IN 8 - Flash - combine with Head signal?
IN 9 - Wash -
IN 10- Wipe -- best left as is, in dash wiring
IN 11- Blower 1 -- best left as is, in dash wiring
IN 12- Blower 2 -- best left as is, in dash wiring
IN 13- Driving Lights
IN 14- Rear Fog
IN 15- Brake
IN 16- Fuel Pump High
IN 17- Defrost
OUT 1 - Dash Light -- best left as is, in dash wiring
Out 2 - Blower
OUT 3 - Left Flasher
OUT 4 - Right Flasher
OUT 5 - Main Beam
OUT 6 - Fuel Level (analog)
OUT 7 - Fuel LEvel Warn

PDM 3 - Door NS
IN 1 - Window Up
IN 2 - Window Down
IN 3 - Lock
IN 4 - Unlock
OUT 1 - Window Up
OUT 2 - Window Down
OUT 3 - Lock
OUT 4 - Unlock
OUT 5 - Mirror Left
OUT 6 - Mirror Right
OUT 7 - Mirror Up
OUT 8 - Mirror Down
OUT 10- Mirror Heat

PDM 4 - Door OS
IN 1 - OS Window Up
IN 2 - OS Window Down
IN 3 - NS Window Up
IN 4 - NS Window Down
IN 5 - Lock
IN 6 - Unlock
IN 7 - Mirror Select
IN 8 - Mirror Up
IN 9 - Mirror Down
IN 10 - Mirror Left
IN 11 - Mirror Right
OUT 1 - Window Up
OUT 2 - Window Down
OUT 3 - Lock
OUT 4 - Unlock
OUT 5 - Mirror Left
OUT 6 - Mirror Right
OUT 7 - Mirror Up
OUT 8 - Mirror Down
OUT 10- Mirror Heat

PDM 5 - Rear
IN 1 - Boot Open
IN 2 - Fuel Level (analog)
IN 3 - Fuel Warn
OUT 1 - Tail
OUT 2 - Brake
OUT 4 - N/S Flash
OUT 5 - O/S Flash
OUT 6 - Brake
OUT 7 - Fog
OUT 8 - Fuel Pump??


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PostPosted: Mon Feb 11, 2013 7:40 pm 
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I like it when people do my homework for me :lol:

Add in rear wash & wipe to 3 of the modules. Plus rear heat. It's a good starting point though, I'll start adding to it when I start looking at it a bit more seriously.

I would be inclined to keep the heater module as standard as there's quite a complexity of actuators, fan speeds etc. Just use a single output so it can be switched off under software control when starting.

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PostPosted: Mon Feb 11, 2013 8:51 pm 
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Need to work of out for the model ;)

I think I can see why some things are state change and some are polled - there's potential for boatloads of traffic if everything runs polled


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PostPosted: Mon Feb 11, 2013 10:04 pm 
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Looking at what I/O is available on the 40 pin dsPIC, I'm looking at:

8 output drives (20A I think) with current sensing for fault report (short or open circuit).
5 analogue inputs 0-5V (or maybe 4 plus power supply sensing)
6 digital inputs.

All inputs will probably have the option to link a pull up resistor to sense contacts / resistive sensors.

Alternatively, maybe double that (minus 2 digital inputs each for internal I2C) to allow double canbus for redundancy.


As regards polled / state change messages, I'm in favour of constant polling in the background to correct errors plus state change messages which take priority in order to keep the system responsive. I'm never in favour of just using state change messages and relying on data at the far end not getting accidentally changed by hardware or software glitch. Such methods are favoured by PC programmers and lead to frequent power off / reboot or right click & refresh.

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PostPosted: Mon Feb 11, 2013 10:06 pm 
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Looking at progressing this a bit quicker so I can get a prototype run of this plus all the board options for the digidash all in one hit.

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PostPosted: Mon Feb 11, 2013 10:19 pm 
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Trouble is you can't do responsive across an io matrix like that using pure polling so state change is a requirement
What you need to know is in a realistic test setup what polling can you get without flooding the bus
Can is also carp - you can't do a direct register rtread as far as I recall. You have to request that the device broadcasts its state and then wait for it to get back to you. Or everything dumps status every so often and a background routine sniffs relevant data

Hence I've built a system model to try a few ideas out


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PostPosted: Mon Feb 11, 2013 10:23 pm 
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From a hardware perspective what I have modelled is each pdm has a bus master and a bus slave
All PDM inputs are connected to the bus master and all outputs are driven by the bus slave. I'll try knock up a quick drawing if you want


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