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Engine Start Button Effects

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indecided

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Hi.

i've got an engine start button, with an integrated 12V light, seperately powered.

my intentions are when the car is switched to accessory (right before u crank the starter), for the light to blink. but when i crank the starter, i want the light to turn solid for the rest of the drive.

the switch has NO/NC outputs.

I was thinking of a circut to first oscillate and create the "blinking". then, a circut to supply constant power to the 12v light, with input being the NO or the NC outputs to "detect" the open/close caused by the engine starting.

in other words..

when the car has not been started but the key is in position, i want the light to blink. when the car has been started (via the starter button), I want the light to stay solid.

any ideas? :)

thanks!
 
by key in position, do you mean just in the ignition, and not turned at all?
Also, what kind of car is it?
 
jrz126 said:
by key in position, do you mean just in the ignition, and not turned at all?
Also, what kind of car is it?

it's a typical honda, 4cyl.

key in position IE accessory/ignition.

hotwaterwizard,

there are two sets of connections. one = +ve -ve for integrated 12V LED
two = C NO NC for switch

i was thinking, with ignition supplied power, the light would blink.
after the starter has been cranked, a circut should detect the cranking and then switch the LED output to steady instead of pulsed.
 
You could also detect when the battery voltage has risen to charging levels. Steady state voltage of a fully charge car battery at about 75*F is usually 12.6 Volts, and probably about 13.8 to 14.5 when charging with no major loads. This way you just need to watch the battery voltage, detect when it is around 12 volts ( car not running ) and then rises to about 13.5 volts ( running ). There will be a short time when the battery voltage drops due to cranking ( in the winter it may drop to about 10 Volts or less during cranking , but will recover fairly quickly) This way you avoid running extra wires to the alternator. This design could use a compartor and a zener to sense the change in voltage.

If you want to run wires to the alternator, there are several different alternator circuits in use, some of which will have connections that will allow you to tell exactly when the engine is running or not. These two types are often refered to as "self-exciting" alternators, or separately "exciting" alternators. The self exciting alternators only have a single main battery connection, and use this to power the the regulator. These alternators will start charging once the RPM's rise sufficiently. Separately wired alternators require an ignition "on" wire to operate, and some have a third wire, to run a voltage sensing line. With these types, the alternator produces charging voltage immediately, or as required by the battery. Using the various wires, you could determine, by the presence of charging voltage in combination with ignition wire voltage, wether or not the engine is running. This design could use "diode logic" to control a signal to the lamp.

So, all in all, what you could do is have a LM339 quad comparator, 1 section oscillating driving a transistor to flash the lamp, another section comparing the battery voltage, and when it rises, drive the lamp steady. You would use 2 diodes to isolate the oscilator and steady drive signals.


Here is the LM339 data sheet with example circuits:

https://www.electro-tech-online.com/custompdfs/2004/10/LM339-DPDF.pdf
 
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