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555 timer car headlights reminder or circuit with adjustable buzzer time off

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BBQ

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Hi all

I'm looking for a circuit preferably 555 timer based for a car headlight reminder that I can adjust how long the buzzer remains on...I was thinking of a positive edge triggered monostable which as you know there several on the web but I can't figure out how I can adopt a circuit to suit.


Cheers
 
You could use an LMC555 timer configured as a one-shot. It's the CMOS version of the 555 and it uses negligible current so you can leave it permanently connected to the battery. It's triggered by a voltage going to 0V so it could be triggered by the ignition switch when it is turned off. To prevent it from triggering when the light is off, connect the light switch output to the Reset input (which resets when its input is 0V). With there is no voltage to the light, the 555 will stay reset and not give an output.

The output can only provide about 10mA maximum so if you buzzer requires more than that you will need to add a transistor buffer such as a 2N2222..
 
He was in the chat earlier asking this same question but seemed to refuse to listen to the answers provided. 3v0 suggested a very similar circuit, except that the 555 would be powered by the headlight circuit, no need to worry about wiring the reset, just tie it to V+ on the 555.

Regards,
Matt
 
He was in the chat earlier asking this same question but seemed to refuse to listen to the answers provided. 3v0 suggested a very similar circuit, except that the 555 would be powered by the headlight circuit, no need to worry about wiring the reset, just tie it to V+ on the 555.
..............
That has the advantage of allowing the use of a standard bipolar 555 if desired.
 
Cheers 3v0 and guys got it sorted,I couldn't grasp it at the time by such an easy solution and ended up overcooking a simple circuit ...I read somewhere that with automotive wiring that there is transient voltages present that could easily damage a 555 timer,I was thinking of a 15 v or maybe higher Zener diode to prevent any issues.

Any suggestions.

Cheers

BBQ
 
Add a small resistor in series with the zener. A 10uF capacitor across the zener will also help suppress any transients as well as decouple the 555.
 
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BBQ:

In the 80's, I made a very simple lights on reminder. Only problem, the buzzer didn't last 17 years and had to be replaced once, The heat killed it.

Here me out. My solution was sound a buzzer when only the Driver's door is opened. OK, so it won;t work if you "go parking" at the park and forget to turn off the lights. It won't work if you exit from another door either.

It's super simple. Most cars switch the 12 V to the head lamps and most cars ground the door switch when the dome light is on. So now, you have an ah ha moment.
Connect a buzzer from the door switch to the headlight relay feed or head light. Well not quite.

In my vehicle, there was a diode on the driver's door for some other driver door function. I wired another diode to the switch for a "diode OR". I also put a 200 PIV diode in series with the buzzer and your done. All of the wiring I needed happened to be in the Driver's kick panel. So, you have (+12 from headlamp), a buzzer, a diode, and yet another diode in series. The other end goes to the door switch. Bingo!
 
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