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Any tips on making a small timed switch?

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I have a project where I need to build a very small switch into a wine bottle cork. The switch would ideally be a button. And the tricky part is it should only remain on for 30 minutes or so. It will be powering an LED.

Wondering if anyone might have any tips?
 

You're probably talking about using a button cell.

It so happens that a battery small enough to fit in a wine bottle cork will probably also have a low capacity, low enough to be depleted after 30 minutes of powering an led.

It's hard to predict whether fried led will occur by connecting it to a button cell (provided its voltage is high enough to run the led). It depends on internal resistance of the battery. You may need to put a resistor inline to protect the led.

There are probably tiny push-on-push-off switches available. It may be just as effective to wedge wires into the cork so they make contact.
 

I've got the resistor and all that worked out, and without a switch my battery powers the led for about a week. It's just the switch that I need help with at this point.

A tiny on/off would do it, but a timer would be so nice if possible.
 

Is this all to fit inside of a fake cork? What voltage is your battery? Do you need an abrupt cutoff of the LED at the end of the time, or could you accept a gradual fade-out?

Ken
 

The battery is 3 volt. Abrupt cut off would be best but a gradual fade out could be interesting and nice too.
 

This circuit uses a white LED. Once the switch is pressed and released the LED will stay on-full for ~25 seconds and then fade out in ~10 seconds. The MOSFET was what I had with a very low Vgs(th). I would trim the tab off and shorten the leads to reduce the height. Someone might have a suggestion for a smaller MOSFET that will work well at 3V. Every one I found that might work were not stocked and could only be ordered in 1K lots. The PB switch was just scavenged from some control panel PCB.

Ken
 

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The OP wants a timed 'on' period of 30 minutes, not seconds. That's too long to be practicable with any analog scheme that I can think of. There's one circuit I designed and used as part of a bigger system that can be readily adapted to suit the OP's requirement except that it uses two CMOS logic ICs and some passive components. I don't think they will all fit in a cork even if SMD versions of the ICs are used.
 

OOPS! Saw it and promptly forgot it. ;) Yeah, expanding my RC x60 would probably not work.

Ken
 

OK, I had to try it. Replaced C1/C2 in my circuit with one 100uF/10V electrolytic capacitor from my junk box. LED full-on time was 30 "minutes", ending with a fade-out over 10 minutes. This is a high-brightness white LED. Power is two fresh 1.5V alkaline batteries. LED Vf=3.17V. Maximum circuit current was 1.35mA. When the LED was off the current was >0.01uA. :)

Ken
 

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