How to Improve Car Headlight Alarm Circuit: Comparator, SMD, IC Options?

Hello Guys!

I was investigating on a car headlight alarm and how it should sound a buzzer when the headlights are on.

I have attached the circuit diagram as well. You might want to have a look on it.

I found this while i was searching for ideas. Now all I need is lots of suggestion from you guyz regarding to how it can be improved.

such as; a pnp transistor has been used can it be improved with a comparator or with any other components?

Are there any other components of this circuit which can be improved?

How can I make it smaller? I have heard about the surface mount techniques as well as Integrated circuits which can make a circuit smaller But I don't have a clue how they work in reality?.

So, I would really appreciate if you guyz could give me a helping hand please?

Colin has a point (in fact that is rather brilliant!) -- but I would add a rectifier in series, with the Anode facing X1 (so the buzzer doesn't sound when the Accessory switch is on and the headlights are off). The 65ma that drives the buzzer _will_ flow through X2, but that shouldn't be enough to make X2 glow.

well i have been doing the electrical stuff for the past couple of years and I am literally new to these electronics stuff so don't know much about them.

well I know what you suggested here would do the job but I am actually tying to make the circuit smaller as well.

so keep that in mind and suggest me something.

I don't see how only a diode and buzzer would be larger than a resistor, transistor and buzzer. As for the drawing I'm a little unsure what the accessory switch and X2 are about. Most cars have ignition and accessory positions. You might not want the headlights to be left on if you're listening to the radio in the accessory position, in which case you should use the ignition position on your switch. What 25W light is on in the accessory position?.

I have used headlights power to sound a buzzer when the headlights are on.

In order to sound the buzzer when the car is off First, a signal source needs to be determined. In the case of my circuit, I chose an accessory line. The accessory line is be grounded when the power is cut (car off) and is otherwise on, so we'll have an easy comparison. Second is the problem of determining when the accessory line is low. I first considered a comparator, but I soon realized that all I would need is a PNP transistor to switch the buzzer on and off. With this component, the headlight line is connected to the emitter, the base is connected to the accessory line, and the collector is connected the buzzer. Therefore, when the headlights are on and the accessories are off, the emitter conducts to the collector and the buzzer sounds. Also with this arrangement, if the headlights are off or the accessories and headlights are on, nothing happens. Additionally a resistor is connected between the accessory line and the transistor to limit the current flowing to ground when the buzzer is sounding.

Mr. Stephen, can i have a circuit diagram please? as I am unable to figure it out on how the accessory line would be connected?

The normal "Headlights Alarm" uses the door courtesy light switch, and sounds the buzzer when you open the door to exit the car leaving your lights on.

Under what circumstances do you want your buzzer to sound ?

I want buzzer to sound when the headlights are on and engine is off. And when the engine and headlights both are on; nothing should happen.

I tried to make the circuit with a diode to stop the current go backward. And this is what I come up with(Please refer to attached circuit). There are two things wrong with the circuit;
1. The current is not going into the buzzer only the voltage does.
2. The current (12Amps) is flowing to the ground which it shouldn't do.

I need your help guyz as I might have put a wrong connection somewhere which is causing the circuit to flow the current to the ground.

Well In that case you want to use the ignition line out to activate circuit so that we can tell if the vehicle is running for testing if lights are on or not

Motor On
Headlight On

So looking at this sensibly
What would do you need to do first and foremost

Maybe the Answer is decide on what your logical sequence of events should be for the buzzer to sound In other words draw up a specification for your project

So now taking this into consideration you need to draw up a truth table ??

Back to the design stage again

Decode On conditions for buzzer to sound
Must a be a buzzer perhaps you vehicle has a flying saucer which is launched from a secret canopy tracking you via GSM, hovering up to you and uttering the words " beep beep beep Errrr Your lights are on and then flies back to the car "

That would be good wouldn't it than just yuck plane annoying buzzer I wish that neighbor would buzz off


Draw up a truth table deciding on what you want to happen and when and also maybe how long do you want this to happen for being as this is a car ( Don't want the battery going flat for either case do we )

Expanding on this design (Thinking forward into the future rather than regressing and being content with just this and also making this far more interesting and challenging )

Would you want to incorporate messaging to advise as you

This might be RF or SMS or direct over the net to a mobile phone, PC, some other person or nominated persons who you might be able to trust (very risky business these days )

Encryption and password authentication possibly springs to mind here Remote control of light situation perhaps you've decided on being notified that you've changed your mind Your car is parked in a high risk area your only going to be a couple on seconds or minutes so you've decided to override this rule and keep your lights on

Individuality !! Far more interesting now than just "Oh a headlight reminder , how boring I mean Ive seen so many of these , blimey thought he might do something a little more interesting )

Provocative , Investigative , elimination , individuality , Interesting , different , positive , attractive , constructive , marketable , successful

fFar better than being just the ordinary copy cat stereo type don't you think

Draw a circuit that corresponds to your logical implementation

Decide on components to use

Test and debug design

Build test and debug design again

That's my approach to this problem

No, like shown in the diagram, below (i.e. "rectifier in series")

BTW: 1N4002, 1N4003, 1N4004, 1N4005 and 1N4006 will also work (I shy away from 1N4001 ever since an ordeal where they keep shorting out due to noise spikes -- an automobile is a very noisy, spiky place ;)

So, the higher the better -- they're cheap!

Only one slight problem here Steve where is your ignition sense ? How does he know the lights are on engine is off for example or conversely Engine is off one light is on and one light is off or engine is off lights are on

Lets show this bloke how to do this properly shall we what do you say to that then " Good point don't you think at the same time we show him Boolean algebra

So for example

Lets call the lights X and Y lets name ignition Z

Logic for this would be ?? Let him answer or let him go away and find out look it up etc etc then he learns

Make him do a truth table showing his conditions Make him do it

The number of years that it took you to reach this level of understanding were not cheap neither are people cheap but its becoming a cheap society with cheap products, cheap performance, cheap training with cheap future total cheap attitudes with very catastrophic failures and and outlook on life that is also cheap

The best answers are not always cheap !! True or false let you think about this Steve don't take this the wrong way It took years and years of hard work and very hard experience to gain this much knowledge

"Your reasons for poverty and destructiveness are now coming to light "

Make him go back to the drawing board and think force him to think make him use his / her brain

If necessary make him cross make him annoyed because The only person hes annoyed with is himself for not thinking and wanting to learn and not listening and not wanting to work LAZY in other words

"Thought Lets get everyone else to do it for him" hence he knows nothing and expects everything for nothing

No appreciation for hard work , its indoors and plays games all day upsets all the neighbors cant be bothered to go to work, cant be bothered to keep himself clean, cant be bothered to make any effort what so ever, hence is a total failure in life, resorts to crime , didn't go to school and eventually resorts to terrorism , bullying etc etc etc

"( Slightly different story for people who have genuinely been worked into the gutter ) , hmmm rather than sitting on their backsides doing sweat fanny Adams " Big difference

Yes I know so, not think so , Know so and finally blames all this on racism, also true in most cases !! Or is a spoilt rich little toffee who had everything handed to them on plate , never done a days hard work in his/ her life and then loses everything on an investment (" typically illegal " winds up in tones of debt and then expects everyone to work for nothing giving them ideas for nothing because he / she has lost its money " Also 100 % true in most cases

Or its gambling !! Also 100% true

X Y Z
OFF OFF OFF
OFF ON ON
ON OFF ON
ON ON ON

I made it on multisim but still there's something wrong with it as the both lights gets on when the buzzer is sounding it supposed to headlights only.
Another thing is the second light glowing a bit more than usual because of the diode (1A 1000v).

All of which are directly or indirectly related to government policies Totally 100% true for the united Kingdom

Bad like queen Elizabeth the second I win you lose "Classic King Edwards versus the Sandringham "

Brilliant well done

So how do they relate to true and false then ?

Now what I want you to do is go and do that next bit lets put this into a table shall we between bq). [code] [/code] tags

Now we also learn how to present information

It might a good idea to include a table scenario for doing just this on the forum see what you think about this recommendation

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When you asked Mr. Stephen for a diagram perhaps you meant me? I would have answered long ago but for some reason the link didn't work until just now. Sorry for all the off topic rants. I never even read responses from some people. I did make a diagram, though it's probably been covered now - there's too much stuff to read.

Your drawing shows an accesory/ignition switch. Commonly these are seperate contacts on the same switch. The circuit I drew requires a significant load to ground to work, which you won't get in the accessory position, so the drawing shows the buzzer connected between the light and ignition switch.

- Stephen

P.S. A recently attached this to an email for fun:

"A small, but vocal, contingent even argues that tin is superior, but they are held by most to be the lunatic fringe of Foil Deflector Beanie science."

and got this (serious or really funny?) response:

"This makes sense to me. Paraterrestrials (also referred to as "aliens" in the popular literature) are known to use psychotronic means of mind control to inculcate humanity to accept their evil agendas. AFDBs will work just as well against these signals as they do against human government and corporate ones."

Armaan, when dealing with Mark, I've found it best to not take anything he says, personally

Ahhh, my mistake. That buzzer (at least in terms of how it is being modeled) draws a lot more than ~66ma at 12V -- the current is being limited by the transistor which appears to have a beta of around 65.

BUT, there are several mysteries:

1. If the lamp dissipates 25W at 12V then it will draw 2.1A at 12V, and 1.9A at 13.3V, so how is 2.3A flowing?
2. How can there be more voltage at the ground side of the buzzer (13.3V) than at the positive side (11.0V). That makes no sense -- unless the buzzer is producing voltage -- which is possible (reverseEMF). I don't know how those probes work, so I don't know, for sure how to interpret those readings.

So, I'm not sure what is going on, there. But, if it's true that the buzzer draws current on the order of 2Amps, then placing the buzzer across the lines that power the lamps won't work.

There are a lot of assumptions being made, here, and I don't have time to sort them all out.

Regarding your request for assistance on converting this to a surface mount design, that's a tall order -- lots of detail to cover. I suggest you search for YouTube videos on the subject.

well, I see both that my drawing didn't make it AND another steve made a perfectly good one. My warning about connecting to the ignition, not accessory, still applies.

Also, this is a simulation. I'm not sure what your experience level is (judging by your reaction to Mark, you're not a beginner but, are you sure that the models in the simulator are reflecting reality close enough for this to be a viable result?

You can get much lower current (and loud) piezo buzzers for cheap from lots of surplus parts places (like all electric or jameco). They would work perfectly with the circuit that was drawn. I didn't see the surface mount comment, but a reply to it. For prototyping surface mount is much more complex - I wouldn't consider it unless you want to make lots of them and are willing to go through the bother of a printed circuit board and connector issues. Even then you should have only two components so there isn't much point.

Armaan, this is a helpful forum, but there is some material from some people that is best just ignored.

There are various ways of doing the job, but this simple circuit will do what you want:

When the ignition switch is on, the relay is energised and the NC (normally closed) contacts are opened, cutting the buzzer off.
When the ignition is off, the NC contact is closed, so the buzzer will sound if the lights are on.

Any small 12V relay will be adequate if you have only a small buzzer. (The relay contacts must rated at or above the buzzer current.)

You can also add a resistor in series with the buzzer to limit the volume.

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(Would an engineer please check my circuit to see if I have forgotten anything ? Capacitors for spike protection, Steve ?)
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Armaan, you had the right basic idea in your original circuit, but the base resistor also needs to go to ground to turn on the transistor. I think this circuit will work. (Attached.)

When the lights are on and the ignition is off, the transistor is supplied with a base current and so switches on, activating the buzzer.
When the lights are on and the ignition is on, the base is taken high (to the same potential as the emitter), so the transistor switches off, de-activating the buzzer.

Your transistor D45H8 has hFE minimum of 40, so I suggest a 4.7 k base resistor for about 2 mA base current to fully saturate it.
(I am guessing there, but I think its about right.)

I HAVE FINALLY MANAGED TO GET IT WORK AND IT'S ALL BECAUSE OF YOUR HELP AND SUPPORT. A BIG THANKS TO ALL THOSE WHO DRAW ME A CIRCUIT DIAGRAM TO HELP ME OUT. I REALLY APPRECIATE YOUR HARD WORK AND HOPE YOU WILL CONTINUE TO HELP GUYZ LIKE ME IN THE FUTURE TOO.

@ Mr. Colin I really appreciate your reply.

@steve thanks mate as you helped me alot with your suggestion and also on choosing a diode and you took some time out from your precious time to draw me a diagram aswell .

@MR. Stephen even though i didn't see your drawings but your explanations were very helpful as you suggested me to use ignition switch instead of accessory line which was brilliant as it worked very well.


@mark I have to say one thing to you pal. if you could change your attitude towards people like me that would be great. As I know you hold a vast of knowledge and it didn't come to you easily but it doesn't cost you anything if you help the needed one? or would it? anyway, it would be an honor for us to take help from you in the future.

@MR. Frank thank you, I really appreciate your drawings. No, that wasn't mine idea I just searched that one on google. I don't want to make a copycat so I was looking for an alternative and the best components to do the job.

HAVE A NICE DAY ALL. TAKE CARE, BYE.