BCS wrote:
> your driving down the road talking about programing language design and suddenly an 18 wheeler starts tail gateing and another pulls out to pass. In the middle of that, your engine starts to splutter, something it has never done before. What is your reaction? I'll give 10:1 that it takes you a few seconds to recognize that the fuel has been cut, remember that there is a switch to override it, find said switch and push it. Now add in that you didn't install the switch (it comes standard) and you have never taking the manual out of shrink wrap. You starting to see why it will never come standard.

There's also a large red light that comes on when oil pressure drops, and a large green light that goes out when the fuel pump is not getting power. Me, I like the interface style where a row of green lights says everything is good, and red lights say things are bad.

As for anyone else, I designed this system for my own use. It's typical for performance cars, you can get the switch at any good speed shop, and is in fact required if you're on the track. Watch drag racing on TV. Sooner or later, probably sooner, you'll see an engine blow up. Turning off the fuel pump automatically only makes sense. Nobody wants to blow fuel at 60 psi onto an engine fire.


>>> So tie it into the inition system or a tilt switch (some 4x4 do that
>>> one).
>>>
>> It is tied to the ignition system already. The problem is, the
>> ignition doesn't automatically turn off when you crash your car.
>>
> 
> Yes the ignition (as the the key) doesn't turn off but when the engine quits running the ignition system (as in the magneto or that block of epoxy and silicon under the hood) quits triggering the spark. Tie into that.

Trying to determine if the distributor is no longer turning is a non-trivial circuit. Best to stick with simple things when dealing with safety issues. The inertial switch is pretty darned simple, it's just a ball stuck on the end of a magnet. Knock it hard, it falls off the magnet, opening the circuit.

Hello Walter,

> BCS wrote:
> 
>> Yes the ignition (as the the key) doesn't turn off but when the
>> engine quits running the ignition system (as in the magneto or that
>> block of epoxy and silicon under the hood) quits triggering the
>> spark. Tie into that.
>> 
> Trying to determine if the distributor is no longer turning is a
> non-trivial circuit. Best to stick with simple things when dealing
> with safety issues. The inertial switch is pretty darned simple, it's
> just a ball stuck on the end of a magnet. Knock it hard, it falls off
> the magnet, opening the circuit.
> 

If you can find the right spot to tie into all you need is an event failure alarm

http://www.elektropage.com/default.asp?page=sub&bid=1&sid=18

A voltage divider across the points for a magneto should work. A more modern system should be even easier as they probably have a low voltage wire somewhere that will work.

Of course all the motivations change if your driving in a race.

BCS wrote:
> Hello Walter,
> 
>> BCS wrote:
>>
>>> Yes the ignition (as the the key) doesn't turn off but when the
>>> engine quits running the ignition system (as in the magneto or that
>>> block of epoxy and silicon under the hood) quits triggering the
>>> spark. Tie into that.
>>>
>> Trying to determine if the distributor is no longer turning is a
>> non-trivial circuit. Best to stick with simple things when dealing
>> with safety issues. The inertial switch is pretty darned simple, it's
>> just a ball stuck on the end of a magnet. Knock it hard, it falls off
>> the magnet, opening the circuit.
>>
> 
> If you can find the right spot to tie into all you need is an event failure alarm
> 
> http://www.elektropage.com/default.asp?page=sub&bid=1&sid=18

No, I'm not going with complex electronics for a fail-safe circuit. A simple fail-open pressure switch is pretty bullet proof.

(Integrated circuits can often have problems in a car - heat, vibration, and spiky power supplies. Using off-the-shelf electronics under the hood can be a problem because of that, you need more robust parts.)

That circuit also has 3 mechanical moving parts, a transistor, a 555 IC, capacitors, numerous connections, any of which can fail. A pressure switch is much simpler.


> A voltage divider across the points for a magneto should work. A more modern system should be even easier as they probably have a low voltage wire somewhere that will work.
> 
> Of course all the motivations change if your driving in a race.