Cartech, please clarify --

Do you want the relay to activate when the signal from the button goes high or when the signal goes low?

Your solution where the on-off is triggered when the signal goes low but not when it initially goes high is exactly what i'm after, thanks.

 

Thanks, however what I was after was a short on-off cycle (not a delay) once the trigger was removed, not applied. The trigger could be on for a period of seconds to hours, my requirement was fulfilled by the circuit provided by Crutschow.

Ok...glad you have a solution.

 

A cheap and easy way to pulse a DC relay is to use a series capacitor. The relay will operate while the capacitor is charging, and then release. You may need a high value resistor across the capacitor to discharge it below the pull in voltage in about ten seconds. Then another button push will once again trigger the relay. Start with 0.47 microfarads is my first guess.

 

They have internet there?

Where did you think all the spammers and scammers came from? Nigeria?

 

The SERIES capacitor does not provide a delay, it only delivers a short pulse while charging current is flowing. One pulse per button press, and after that nothing until after the button is released and the capacitor is discharged by the resistor.
But after going back to post #1 it seems that the intent is to deliver that short pulse when the ignition is switched off.
To do that takes the same arrangement but different connections. The pulse relay will be in series with the capacitor ACROSS the ignition switch, so that when the switch is opened the capacitor will be charged by the current flowing through the relay and the ignition system load,which I am presuming will draw enough current for that brief period while the capacitor charges.

BUT unlocking the doors when the engine switches off is a really poor choice! In fact, I will go so far as to say it is a TOTALLY STUPID choice because it allows a bad actor the chance to yank open a passenger side door and steal the laptop computer off of the back seat.

 

... unlocking the doors when the engine switches off is a really poor choice! In fact, I will go so far as to say it is a TOTALLY STUPID choice because it allows a bad actor the chance to yank open a passenger side door and steal the laptop computer off of the back seat.

Thanks, I'll pass your opinion on to the vehicle manufacturer who (on later models) have provided the functionality in software to unlock all doors on key-out, I'm sure they'll give it the consideration it deserves.
When do you suggest the doors are unlocked?

 

Thanks, I'll pass your opinion on to the vehicle manufacturer who (on later models) have provided the functionality in software to unlock all doors on key-out, I'm sure they'll give it the consideration it deserves.
When do you suggest the doors are unlocked?

The drivers door should unlock when the driver moves the inside handle to open the door. Likewise for any passengers. OR, if there are no passengers, then when the driver presses the unlock button.
On my vehicle, a 2017 Caravan, ALL the doors unlock when the driver moves to open the driver's door. This permits the bad actors entrance if the driver does not instantly hit the All Lock button after starting to open my door. I realize that not everybody has to deal with bad actors, but in some places they seem to abound. And it is not the best feeling to need to carry a sidearm and really bad to need to use it. How about a system to electrify the car on command so that the bad actors would refrain from grabbing the door handles? I am sure that it is against the rules for this site.

 

I think this thread reached the end of it's usefulness with post No. 22, thanks everyone.

 

The drivers door should unlock when the driver moves the inside handle to open the door. Likewise for any passengers. OR, if there are no passengers, then when the driver presses the unlock button.
On my vehicle, a 2017 Caravan, ALL the doors unlock when the driver moves to open the driver's door. This permits the bad actors entrance if the driver does not instantly hit the All Lock button after starting to open my door. I realize that not everybody has to deal with bad actors, but in some places they seem to abound. And it is not the best feeling to need to carry a sidearm and really bad to need to use it. How about a system to electrify the car on command so that the bad actors would refrain from grabbing the door handles? I am sure that it is against the rules for this site.

I think the situation the TS describes is the more common than you think. At least, in the last two vehicles I’ve owned, I pull up to park, place the transmission in Park and remove the key. The doors automatically unlock.

 

I pull up to park, place the transmission in Park and remove the key. The doors automatically unlock.

Mine uses a FOB, I place in park and the doors unlock.

 

Mine uses a FOB, I place in park and the doors unlock.

My vehicle works the same way...place in park and the doors auto-unlock.

 

My vehicle works the same way...place in park and the doors auto-unlock.

I hope that neither one of you has the misfortune of unlocking when a bad actor is ready to do it's thing.

 

I hope that neither one of you has the misfortune of unlocking when a bad actor is ready to do it's thing.

Heh....let them try.

 

@crutschow Put this together today - works perfectly - thank you.

 

Here's a solution that uses two relays.



When the ignition switch is on, the first relay coil is energised and the capacitor gets charged.

When the ignition is off, the capacitor gets discharged through the second relay coil to generate the pulse.

Nandu.

 

Here's a solution that uses two relays.

View attachment 270507

When the ignition switch is on, the first relay coil is energised and the capacitor gets charged.

When the ignition is off, the capacitor gets discharged through the second relay coil to generate the pulse.

Nandu.

this is a variation of the suggestion that i made in post #25. It is probably better because it does not leave a sneak path from the battery to the "engine run" circuit, which simply putting a capacitor in series with the relay across the ignition switch would do. But it is a bit more complex, and uses more power, so there is a trade-off there.