Timer project.

[mzustdds]

I am new to this forrum, I'm trying to design a circuit that will start the heated seats on a car. My idea is to use a timer circuit. I have been reading about 555 circuits, but I have the following questions.

It seems that the trigger for the 555 is a negative connection, can the 555 be triggered by application of positive voltage? If it can, my idea is to have the car's starter motor circuit trigger the timer, have it wait for five seconds (enough time for the car to start) then have the output of the timer activate a relay for .5 seconds. (I would use the relay to contact the heated seats switch)

Can someone help me with a suggestion?

Is there a better way than this idea?

Thanks in advance for any help.

 

[mytech]

Yes you can turn 555 to active when positive applied by connecting an inverter..

 

[KMoffett]

Add a resistor in between the +input signal and the transistor's base in mytech's circuit. 10K should do OK.
Ken

 

[MrDEB]

add a temp sensor

then your seats will only heat up when its cold.
I would wait longer than .5 seconds to turn on the seats.
What happens if the car dosn't start right away. your seats will be drawing power then.
instead of the starting circuit, tie your circuit into the cars RUN , IGN circuit.
That way the seats will start heating up AFTER the car has started.
temp probes are simple.
just a few suggestions

 

[RODALCO]

You can do the voltage sensing when the car is running via a zener diode circuit which will trigger your timer when the battery voltage is above 12.6 - 13.0 Volts.