Programmable devices and SVA.

[steamyrotter]

This may be one of my sillier posts (and that is saying something)

What's the stand on software control on vehicles wrt SVA?

As I am building a viper I don't want anything too easy on it........

Thinking along the lines of either PIC or miniPLC for some functions but not sure whether to do this from the start or post SVA

Cheers

Dean

[snake_bitten]

I can't say for sure, but for what it,s worth here are my thoughts......say for example you are building a Dax DeDion and decide to use the XJ40 donors wiring system. Every switch on the car is microprocessor connected and logic switching........would it fail the SVA?

How could it? If when opperated the switch has the correct result e.g. fan on = air blowing from the vents how will the inspector know? after all engine ECU's are to a greater or lesser extent programmable. mine is fully mappable for fuel, timming, traction control, NOS, fan and many more that I will never have need for.

Provided you are not thinking of Electronic control of saftey critical systems such as steering and brakes

My thoughts on the question only and I would recoment you get a definitive answer (as far as possible) direct from the SVA tester you plan on going to. I have found them quite helpful (when you can actually get hold of them).

Good luck and well done for daring to be different:thumb:

[chesterak]

Not to put a damper on your enthusiasm, but, I would question using equipment that is potentially unreliable. My brief experience with PIC's, assembly language, burning EEPROM's etc is it is something that I would not want to install in/on a car. Going for simple devices; switch made=light on makes more sense to me. The modern programmable speedo's and rev counters may have some form of configurable electronics inside and they are no doubt reliable - but for most applications simplicity is best, in my opinion. :thumb:

Just imagine; a programmable hydraulic suspension system and we could have some famous dancing Cobras

[Grease Monkey]

Quite some time ago i worked with a hardware bloke who had done some work with Jaguar to reduce wiring in cars.

The theory was to run a single power line to everything, and a single signal line to everything. Each item would then have a small RS232 (or equivilent) chip built in, and you simply send a signal along the wire to every device on the bus saying 'headlights on' or 'right indicator off' etc and the individual component would detect the signal and switch itself on or off.

Massive saving on wiring when you realise how many miles of wire is used in a modern car. The problem was only discovered when the car was driven in to the vicinity of a strong electro-magnetic field, ie under HT power lines, when everything went totally screwy. Project dropped.

Admittedly this was some years ago, and i'm sure shielding technology has moved on from the early days...

[hfbradley01]

There's an old saying - kiss (keep it simple stupid)

Cheers

[Happy Jim]

Admittedly this was some years ago, and i'm sure shielding technology has moved on from the early days...[/quote:8987eefc93]


A little perhaps

http://www.can.bosch.com/

[hfbradley01]

Hi Adrian

Good luck with the SVA m8y

Howard

[Grease Monkey]

Jim, That'll be the system then!

Howard, Cheers, still dashing around the garage fixing all those last minute screw ups.

[Andy302]

Originally Posted by Grease Monkey

Quite some time ago i worked with a hardware bloke who had done some work with Jaguar to reduce wiring in cars.

The theory was to run a single power line to everything, and a single signal line to everything. Each item would then have a small RS232 (or equivilent) chip built in, and you simply send a signal along the wire to every device on the bus saying 'headlights on' or 'right indicator off' etc and the individual component would detect the signal and switch itself on or off.

Massive saving on wiring when you realise how many miles of wire is used in a modern car. The problem was only discovered when the car was driven in to the vicinity of a strong electro-magnetic field, ie under HT power lines, when everything went totally screwy. Project dropped.

Admittedly this was some years ago, and i'm sure shielding technology has moved on from the early days...

Its a system used by a lot of people now, called CAN bus, other manufs have their own versions but CAN is industry wide and proven.

[oglyoodoo]

Dean

I personally don't have a problem with microcontrollers in cars. My own tin top is said to have about twenty of them controlling various things. My GD will have around 4.

Most of the concerns many people have is caused by a lack of understanding about the hostile environment car electronics experience. This is not just about temperature and vibration but about high voltage transients on the supply and control lines, the possibility of strong RF fields, as GM pointed out, and other factors. Knocking up a a circuit on Veroboard and stuffing it in a plastic box is not likely to produce a reliable system.

In a past life I have come across a good many badly designed electronic items used in Police cars. On a new Rover SDI a light appeared on the Dashboard indicating a rear light failure whenever Mr plod went to transmit. I spoke to the company and they hadn't got a clue how to fix it. If you find a fix will you let us know!! This we did. On a Granada all doors locking when using a radio to transmit and on early Volvos with fuel injection the car suddenly slowing down when transmitting. Thankfully manufacturers are much more aware of these problems and these days systems have to be properly EMC (Electro-magnetic compatibility) tested and certified, or supposed to be! There are in fact some ridiculously stringent EMC tests specified for some automotive electronic products which doubtless many don't meet.

I have dozens of systems I have designed using PICs located in many countries and to date not one failure. One of the more recent projects was required to be independantly certified and this cost over £5k just for the testing . Thankfully it passed first time.

PICs are an ideal microcontroller for semi critical things being based on the so called Harvard Architecture. Simply put the controller can't get into a pickle trying to execute random data instead of instructions. It also has a Watchdog timer, which if enabled will time out and restart the program if it is not reset every few milliseconds. So in the very unlikely event of it getting hung up, it will restart things assuming the code is written properly. These microcontrollers are not like PCs which get the blue screen of death and hang for no apparent reason. When was the last time your TV remote got hung up?? That almost certainly has a Microcontroller in it.

Another car I built has a good many electronic gizmos one of which saved the engine when I lost the water!! Within a few seconds an Audible alarm told me something was seriously wrong. No drama no serious overheating, no warped head (except mine !!)

I wouldn't dream of using a home built electronic system for anything safety critical as snake-bitten says but microcontrollers do IMHO have a part to play in adding additional facilities and warning of impending failure such as loss of oil pressure, over temperature, lamp failure etc. Indeed it is not too taxing to detect failure of any lamps even whilst they are not actually switched on... Similarly it is possible to detect overcurrents and switch off a circuit long before a fuse has had time to warm up and blow. What about self cancelling indicators and Headlamp flash without having additional switches on GDs.

Dean, I wish you luck with your Microcontrollers just make sure that it is robust, located where it is relatively cool, pay attention to using a proper voltage regulator specified for automotive use, decouple things properly, use transient suppressors on all control and supply lines preferably opto isolate the control lines, put it in a metal box in fact build it like a brick privvy and finally single step the controller to make sure it doesn't get hung up anywhere easier if you use Assembly language Compilers have errors!

Denis