Mailbox light :)

[daviddoria]

we live on a huge hill so big that we generally drive down the driveway to get the mail. My dad asked me to make him a light in his office that would turn on when the mail had come, because he was tired of going all the way down and it wasn't even there yet. as i never could get the receiver/transmitter i was working on so long ago to work, i told him the best i could do was make a light on the mail box that he could look for with his telescope.

the problem is when the mailman is done, he closes the box lol

how do i make an LED turn on when the circuit is broken, then remain on when it is closed again?

thanks
david

 

[lavenatti]

Use an SCR.

 

[daviddoria]

how do i do that?

 

[Sebi]

A possible solution in Projects Forum.

 

[Phasor]

This is basically what you want. The SCR can be any type. The switch on the left, is a microswitch, mounted so that it is electrically open, when the mailbox is closed, and electrically closed, when the mailbox is open. The reset switch turns the light off when you check the mail - it's an NC momentary switch. Resistor values aren't critical - I just pulled those values out of my head.
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EDIT: Sorry Sebi - I didn't see your post in the other forum till later - seems you've already answered it But mine has zero quiescent current 8)

 

[Gene]

What if you put the trigger switch in the mailbox and hard-wired it to the rest of the circuit in the house? It would be kind-of like the transmitter idea. Oh yea, get your Dad to spring for the wire.

 

[daviddoria]

haha i wouldn't be worried about the cost of the wire... just the actual wire running all the way up to the house could cause a problem with lawnmowers, weekwackers and the like

and i dont want to burry it i'm too lazy hehe.

 

[kinjalgp]

If distance is not very long then you can use Infrared to transmit signal (Upto 15 meters) or you can also use laser diode (Upto 1km).

 

[daviddoria]

ahh... 1 km is sounding good.... what do i ask for at the electronics store? laser diode and laser receiver diode?

will this go through a window? or should he go outside to aim the receiver?

 

[kinjalgp]

You should ask for Laser Diode which has output less than 5mW. The receiver is simple visible light photo-diode or photo transistor. LASER cannot pass through windows. LASER is a point source of light and you need to aim your photo-diode exactly at the beam. In case of infrared you need not worry about point accuracy.

Look at this Jameco page:
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This one I think will best suit your application:
**broken link removed**

 

[daviddoria]

hmm maybe what i do is have 2 laser diodes...

1 that is always on and 1 that turns on when the mail has come... so he knows if he is successfully pointing at the diodes...

like a "connection established" light and a "you have mail" light.

how would i differentiate between the 2 beams?

 

[kinjalgp]

You don't need to use 2 laser diodes. One is sufficient. All you need to do is fix the photo-diode firmly on top of the window or terrace where no one can disturb it. Same should be done with the laser diode. Once properly aligned, it won't require to be touched any more.