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auto shutoff reading light. 12v dc power supply-momentary switch-1.2 Farad Capacitor--small LED reading light-? Answered

How long would the lights stay on, how long to charge the Cap?  I want to make something for my kids, so they can turn on a reading light in their bed by pressing a button and then have it shutoff about 30 minutes later when they are sleeping, or press the button again if they are still reading.  I like to encourage them to read.



Best Answer 8 years ago

You'd be better to run it off of a battery, and using a timing circuit. I wouldn't reccomend setting up a monostable to run for half an hour, but if you hook up an astable to a decade counter, with the last output being inverted, then connected to a transistor.

The on switch can be a standard push button, and should be connected to the transistor (uninverted) and the reset of the decade counter. The transistor itself should be placed in series with the rest of the circuit so when it is turned off, the circuit is turned off.

Would you consider putting an X-10 home controller module on the desk lamp? It could be cut off via timer from a signal on the home computer, or just kill that switch module with a push of a button (remotely) when you go to bed. (Sorry I was not able to help with the timer question itself.)

If your kids are reading instead of sleeping, why not have them in the same room as you so you can help.Bed means bed then, if you establish after-bed activities as OK you might create problems in the future (kids can find ways around your lighting devices as they mature)


These lights are for my older (8 and 10 year old) boys, I don't mind having them read for an hour at night.  I want a better solution then them leaving their desk lamps on all night and I don't want a battery that I have to replace all of the time.  So I guess that I will have to find a timer and make that work.

...why not have them in the same room ?

Yea, right. 


(yes I get it..) But what happened to fathers reading bed-time stories, like Black Bartlemy's Treasure?

Sing this to the tune of The Blaydon Races:

One by the knife did part wi' life
And three the bullet took O,
But three times three died plaguily
A-wriggling on a hook O.
A hook both strong and bright and long,
They died by gash o' hook O.
A hook both strong and bright and long....
They died by gash o' hook O.


Nice little nursery rhyme to lull the little buggers to sleep. Remind me never to ask you to babysit.


Yea, well my sister remembers that one, I don't.


As Mathews says, better to have a timer -and a lock out switch. My 9 year old was still reading at midnight last night.