Need help with a 555 timer. Using it with some car interior lights

[Kirbot]

Well... I just got kicked from another circuit forum for wanting to "modify" my car with this. But, they sent me here, and this place seems to be a lot more active anyway!

I do know a decent amount about wiring, and I'll be using fuses and keeping this safe... But I don't know anything about circuits.
I've been reading about the 555 circuit, and I know what capacitors are and basic thing like that. But that's about where my experience ends. So... I'm hoping somebody can lend me some patience with this...

I have an classic car (actually a 1981 CJ7), that I've been trying to add some modern touches to.
I'm planning on adding power door locks, and I'm hoping I can take the 12v pulse (that unlocks the doors) from them, and use that to activate a 2 minute timer which would power a relay and turn on some interior LEDs.

That much seems simple enough, but I'd also like to tie into the ignition, so that when I turn on the ignition and start the engine, it sends 12v into the circuit and shuts the light off again (before the 2 minutes are up).
And the final complication, is I don't want the lights to come back on when I shut the engine and the ignition off. (finally completing the 2nd 12v "pulse")


Has anybody done something like this? Would it be simple enough for an electronic incompetent to solder together?


I might even make a 2nd circuit that would turn the headlights on for about 10 seconds powered by the "unlock" pulse. But I'm thinking that should just take a standard 555 circuit that I kind find the schematics for.

 

[cowboybob]

Welcome, Kirbot!

Sorry for the delayed response.

Your idea has merit.

Two 555 circuits, (555s, appropriate components and a relay) one configured as a "flip-flop" (FF), triggered by the "unlock" pulse and the other 555, configured as a "one-shot" and timed for a 2 minute (or whatever time) duration to reverse the first 555, could be used to power the LEDs. This circuit would self reverse on time-out.

An additional, simple relay trigger circuit (if triggered within the 2 minute "hold" time of the 555 flip-flop) say, tied to the starter "Bendix" acutator connection, could then be used to reverse the condition of the 555 flip-flop, thereby during off the LEDs.

All of this powered from an "always hot" vehicle line.

Not a difficult circuit to create, but that, of course, depends on your level of expertise.

You could probaby use the head light circuit you mentioned, slightly modified. Won't know until you give us some more details as you go along.

Glad to help, though, to get you started.

 

[Ian Rogers]

Yes! welcome to the forum..

I read this about 6 hours ago... I was hoping someone would chip in.... I would have responded, gut My idea would have just been a micro..... As this isn't the answer, I waited...

 

[alec_t]

Which country are you in? UK insurance companies are likely to disown you if you do any mods to a car's wiring which could (in their view) compromise safety.

 

[Kirbot]

I'm in the USA, New Jersey to be exact. The vehicle is registered as a Classic, so it doesn't even have to get inspected.
With all the winches and driving lights people wire into these things, I don't really think a glorified light switch should cause any problems.


Anyway.... I'm ALMOST following you cowboybob.

Basically, 3 separate circuits wired together.
I see the flip-flop is turned on and off by a 12v pulse, but presumably there's no timer in it?
I start that with the unlock pulse.

But the one-shot has the actual timer, also started by the unlock pulse.
Does that send another pulse to the flip-slop to shut it off after two minutes?
This is the part I can't quite figure out..


I'm not sure what you mean by a relay trigger circuit, but I'd assume it's something to convert the "ignition on", into a pulse?

If the one-shot does work by pulsing the flip-flop to shut it off, couldn't the ignition relay shut the flip-flop off, and then later the one-shot times out, and restarts it?



One more thing just occurred to me.
If I hit the unlock twice, either just out of habit, or to unlock the passenger door, (I don't have the remote unlock kit yet, so I'm 100% sure how it works)
Is that just going to restart the timer, and not really affect anything, or will it turn the flip-switch off, later to be turned back on the by the timer or the ignition, basically... screwing everything up.

 

[cowboybob]

Here's the theory:

1. The 555 FF, attached to an always "hot" line at installation, is configured to "latch" its output in the "OFF" state .

2.A. On receiving the unlock pulse the FF "flips" to "ON" so that the output goes high. This output powers both the LEDs (by way of a FET to handle the current) AND powers up the second monostable 555 two minute timer.

2.B. If the car is not started within two minutes, the 555 timer "times out" and sends a pulse to the FF, reversing its state to OFF, which removes power from LEDs AND the timer.

2.C. Or, the car is started within two minutes, sending a trigger (via a relay being energized) that flips the FF to an off state which has the same effect as 2.B. above.

If I hit the unlock twice, either just out of habit, or to unlock the passenger door, (I don't have the remote unlock kit yet, so I'm 100% sure how it works)
Is that just going to restart the timer, and not really affect anything, or will it turn the flip-switch off, later to be turned back on the by the timer or the ignition, basically... screwing everything up.

It might. Depends on if the remote lock/unlock system has separate trigger/power wires to the locking mechanisms. We'll cross that bridge when you get there.

 

[alec_t]

I think you can get away with a single 555 timer circuit, as per the attachment.
The 'Door unlock' pulse turns on Q1 to provide, via C2, a brief trigger pulse for the 555 and so energise the relay coil.
The 'Ignition on' voltage resets the timer, via Q2 and C3, thus de-energising the relay.
Repeated actuation of the unlock pulse re-triggers the timer.
Turning off the ignition won't re-trigger the timer; the lights, if on, will stay on until the timed period (adjustable with the trimpot) ends.

Edit: I assumed a relay coil current of ~100mA in the sim. The 555 maximum output current is ~200mA, but it would be better to use an additional driver transistor for the relay if it is current-hungry. Depending on the lights you want to switch you may be able to dispense with the relay and drive the lights directly from the 555.

 

[cowboybob]

alec_t,

Your's is more elegant, I must admit.

I can, at times, over-engineer my circuits.

 

[Kirbot]

Wow, sounds perfect. Thanks! (Both of you)

I've been staring at that schematic for the past 10 minutes, and I do have one or two questions, but I think they can be answered just reading up on how to read schematics.

I won't get a chance to actually wire this up in the jeep until sometime this summer.
I want to rebuild the doors and the entire interior, then I'll have a chance to work on the wiring.

But, I think I'll try to put this circuit together ahead of time. I'll try to get to an electronics store (or at least a radio shack) next week and see if I can pick up the parts to make this.


One question, what kind of board will I be putting this together on? I've heard of a bread board, but that looks like a more temporary thing, just for setting up and testing.

 

[4pyros]

Something like this with point to point wiring;
https://www.radioshack.com/product/index.jsp?productId=2104052