🚀 go-pugleaf

DaveC wrote:
> 
> I want to make a circuit that will sound an alarm when oil pressure goes to
> zero, or temperature goes to max. The alarm must not trigger for about 10
> seconds after I turn on the ignition. (I don't want the alarm to sound before
> I start the engine.)
> 
> The simplest circuit seems to be:
> 1) a relay triggered by the oil and temp idiot light circuits, that sounds an
> audible alert
> 2) a relay that provides power (or ground) to relay (1)'s coil
> 3) an R-C circuit that delays the activation of relay (2) for about 10
> seconds.
> 
> Is there a simpler way to do this? With just one relay, and that relay's
> activation delayed by the R-C?

Good idea.  1 relay, resistor, capacitor, zener and transistor.
Connect the R & C in series - one side to + that gets switched
on with the ignition, the other side to ground.  With a 9V zener
connected between the base of the transistor and the junction
of the R & C, the transistor can turn on after the RC time delay
charges the cap to the point where the zener conducts. That
"satisfies" one side of the relay coil. The other side connects
to the idiot lite. If you want to use more than one idiot lite
to trigger the alarm, install diodes between the idiot lite and
the relay coil.  You'll have to determine how the idiot lites
are switched - either + or minus can be switched (but my bet,
based on limited auto experience, is that the minus is switched).
Once you know how they are switched you can design the transistor
switch to switch the opposite polarity.


> 
> Any suggestions would be greatly appreciated.
> --
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> 
> Thanks,
> Dave
> ---
> Dave Carpenter
> Sound Logic
> voicebox@d8n8a8i.com
> 
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