Asked this in another thread but it was combined with another question and never got an answer...

I am looking for a VERY simple circuit to switch off an interior or glovebox light if the door has been left open (eg overnight) to prevent battery going flat, light burning out,. melting enclosure etc

There are gazillions of circuits on the web but all seem to use a trigger. I need one that does not need a trigger. Just connect 12V , output on instantly, then after 10 mins switch output off even if the input is still on. If input is off, of course, switch output off.

Found one on youtube but it seems excessively complicated, using a REED relay to keep the trigger closed. Is there a simpler circuit that achieves this? The load is very small, an LED interior light - 50-60mA maybe or less? Do I really need a relay? If so, I'd like the relay to energize at start and de-energize afert 10 mins else there is no point (relay will draw current). Generally the less components the better - 555 Ok I guess but why is it necessary (eg transistors take more power?). CMOS 555 also Ok although I'm afraid of toasting it when soldering.

Heres the youtube circuit ... I could do without the relay probably, but can I avoid the reed...? <10 mins (eg 8 mins) also good, I know theres a prob with long delays and 555s...



Many Thanks!

 

This is my favorite circuit for long delays (Circuit 2).
It starts the timeout when power is applied and will turn off the LED after that.

You would make the "Range" connection to pin 6 for 10 minutes or so.

The transistor can power the LED without the relay, but use two transistors (e.g. 2N2907) in a Darlington configuration or a small P-MOSFET for currents over 40mA.

 

How is the existing LED interior light wired? Are you trying to use the glove box switch to activate?
SG

 

Ah yes... the 4060...thanks but i'd like something controlled by the 12v supply.. no reset or other buttons

SG - yes, I have a pin switch in series with a fuse a small COB led light right now for glovebox light./ The car does have dimmer and timeout for its own domelight (Honda Jazz / Fit 2015) but it is not easy to find that wire to tap into it, new cars are a nightmare for that...

Discharging a capacitor for 10 minutes would work, but I'd need a capacitor larger than the car itself probably - hehe

(I also have an older car with a normal on / off / door dome light, I'd like something like this for that one too, but that one's got an LED array not COB so that takes more juice to operate so probably a relay)

(BTW I did buy a small circuit off Ebay from a guy in Bulgaria however I got the wrong circuit , which switches ON after 0-480s... I can use the NC contact of relay but the relay stays on forever then and takes more current than the tiny LED most likely.. I am trying to reverse engineer ff it and maybe change it to delay OFF from delay on, but that takes time (I'm not very good) and may be a lot more work to do than from scratch)

 

Ah yes... the 4060...thanks but i'd like something controlled by the 12v supply.. no reset or other buttons

As I stated previously, the circuit starts timing when power is applied.
The Reset button is optional and would not be used for your application.

 

I see - Ok I'll look into it - Thanks!!

 

I might add that C2 and R6 reset the circuit when power is first applied.

 

(I also have an older car with a normal on / off / door dome light, I'd like something like this for that one too, but that one's got an LED array not COB so that takes more juice to operate so probably a relay)

A P-MOSFET of the proper size could readily handle the current.

 

Umm I am a bit confused about the two LEDs, Yellow and Green - they are used to set up long times I understand...?

The setup procedure is unclear to me... - that arrow going to the table means what? connect to pin X for delay y?

And if I remove them I just connect the two resistors to the ground, or ...?

Anyway I try to read and understand but really just a solution for say 10 mins and no LEDs (to minimize the power consumption) woudl be great - what pin to connect , where etc

 

I am a bit confused about the two LEDs, Yellow and Green - they are used to set up long times I understand...?

Yes, they are used to set the oscillator frequency without having to wait for the total timeout.
If you don't want the LEDs (you can use a meter to detect the signals) then just leave out the LEDs and associated resistors.

The setup procedure is unclear to me... - that arrow going to the table means what? connect to pin X for delay y?

Yes.
As I stated, for a 10 minute delay you would connect that point (junction of R7 and D1) to pin 6.

Edit: For your relatively short time period (compared to the maximum the circuit can do) you could use a smaller timing capacitor.
For example a value of 1μF for C3 would speed things up about 10 times.
Then for your delay you would connect to pin 15 instead of pin 6.

 

Discharging a capacitor for 10 minutes would work, but I'd need a capacitor larger than the car itself probably - hehe

Not if the capacitor is connected through a pair of transistors as shown below. With the components listed I was getting almost 6 minutes.
SG

 

Ok, I see - thank you

SG: Interesting!! What is the max load (mA) instead of the relay coil?

EDIT I see 30-37mA for the coil, so I could operate a tiny led for the glovebox from it? For the dome light, relay I guess.

It is not 10 minutes and probably the capacitor leakage will reduce the time as well (?) but it is quite simple

 

Not if the capacitor is connected through a pair of transistors as shown below. With the components listed I was getting almost 6 minutes.
SG
View attachment 144967

Don't see how you can get 6 minutes when the time-constant of 470kΩ and 100μF is only 47 seconds.

 

Don't see how you can get 6 minutes when the time-constant of 470kΩ and 100μF is only 47 seconds.

You also have the input impedance of the darlington and the holding current of the relay in effect.
You can operate the LED directly, but will begin to slowly dim after a couple of minutes.
The value of the components can be changed to get a longer time delay.
SG

 

See

 

You also have the input impedance of the darlington

That's just two forward-biased diodes in series, which have a low impedance.

 

That's just two forward-biased diodes in series, which have a low impedance.

True, but it also takes more then one time constant to fully charge and the dropout voltage on the relay is only 3.5 volts.
SG

 

Option #12 for this https://pac-audio.com/catalog/specialty-items/tr7 device ALMOST works.

Max time is 4 min 12 s unfortunately.

 

True, but it also takes more then one time constant to fully charge and the dropout voltage on the relay is only 3.5 volts.
SG

Okay.
But I'm concerned about electrolytic capacitor leakage current being a problem at such low discharge currents.

 

Option #12 for this https://pac-audio.com/catalog/specialty-items/tr7 device ALMOST works.

Seems rather expensive to use for just a time-out function.