Making alloca more safe

[Walter Bright]

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.