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"DaveC" <anon@example.net> wrote in message
news:0001HW.B97FE8A5001B1B1E09D78310@news.covad.net...
> 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?
>
> Any suggestions would be greatly appreciated.
> --
> Note that my return address is corrupted in an attempt to reduce spam. If
you
> choose to e-mail me, please correct my address as described below.
>
> Thanks,
> Dave
> ---
> Dave Carpenter
> Sound Logic
> voicebox@d8n8a8i.com
>
> Remove the numbers to reply via e-mail
>
Hi,
This sounds like a good idea.

A couple of things;

The turn on delay would only need to be on the oil pressure sender, because
if the engine temp is already at max when you go to start it, there is
something seriously wrong.

Most temp senders are a themisters used to drive the temp gauge in the
vehicle. Hotter the temp the lower the resistance of the termistor. Voltage
at the themistor terminal gets less (closer to 0V) as the engine heats up,
but it may not reach 0v, you will need to work out what voltage represents a
high temp. You will also have to be carefull as any low impedance
connections to the sender output will change the reading on the dash temp
gauge.

O.T.
Also, in many cars the temp sender is in or near the themostat housing at
top of the engine. This can prove a problem if the coolant rapidly drains
from the system due to a burst hose, water pump seal, etc. I have heard of
several stories where the temp gauge read as "normal", yet all the coolant
had drained out of the engine and the engine seized.

Reagrds
Paul