I'm looking for a little help with an April fools prank in the works. I'd like to have a small computer fan with a battery placed inside of a box covered in glitter that when the box is opened the fan turns on and blasts glitter everywhere. I can not figure out how to have the circuit close once the lid is open. This is one of those times I wish I had payed more attention in electronics class. Any help would be appreciated.

 

I'm looking for a little help with an April fools prank in the works. I'd like to have a small computer fan with a battery placed inside of a box covered in glitter that when the box is opened the fan turns on and blasts glitter everywhere. I can not figure out how to have the circuit close once the lid is open. This is one of those times I wish I had payed more attention in electronics class. Any help would be appreciated.

If the box is going to be opened in a bright enough environment, you could use an LDR (light dependent resistor) to make the fan go on once the box is opened and it is exposed to some light. Using this method, the circuit would always be closed, but the resistor would dissipate nearly all of the voltage until the box is opened.

Warning: If you're doing this quickly for just one time, my suggestion might work, but otherwise, it might not be a good idea to do it this way. If the box was left closed for too a long a period of time, the resistor could generate a lot of heat and possibly even start a fire.

 

If the box is going to be opened in a bright enough environment, you could use an LDR (light dependent resistor) to make the fan go on once the box is opened and it is exposed to some light. Using this method, the circuit would always be closed, but the resistor would dissipate nearly all of the voltage until the box is opened.

Warning: If you're doing this quickly for just one time, my suggestion might work, but otherwise, it might not be a good idea to do it this way. If the box was left closed for too a long a period of time, the resistor could generate a lot of heat and possibly even start a fire.

Thank you for the reaponse. Unfortunately I'm sure the box would be sitting on their desk for quite a while before they got to opening it. Even though the potential of a fire would be a little more interesting than some glitter, the repercussions of that wouldn't be worth it. Any other ideas?

 

Basically, you'll need to create something that works like the light switch in a refrigerator. A quick Google search showed this thread (on a different forum), which appears to be the exact same sort of question. Hope this helps.

 

Two paper clips attached at opposite ends and overlapping slightly. Insert a short tab between them and feed it through the box top and tape in place. Wire the two opposite ends inline between the battery and fan. This makes an NC switch held open by the tab. When the cover is opened, the paper clips contact and turn on the fan. Or something like this...

 

Just need a switch..
One that is normally closed when the switch is not pressed..

 

Microswitch with a long lever.....

 

I've been thinking way to hard into something so simple. I wanted to avoid using a switch in case it got bumped around to much and went off before hand. I'm going to rig something up like djsfantasi suggested where once the lid is open a tab will be removed and close the circuit. Thanks for everyone's help!

 

Two paper clips attached at opposite ends and overlapping slightly. Insert a short tab between them and feed it through the box top and tape in place. Wire the two opposite ends inline between the battery and fan. This makes an NC switch held open by the tab. When the cover is opened, the paper clips contact and turn on the fan. Or something like this...

That's what I would do. Much like many new products come with a plastic film tab between a battery terminal and the line to the battery terminal. Pull the tab and the contacts are made.

Ron

 

You won't be able to "blast glitter everywhere" with just a small computer fan. They have very little power. Did you try it first?

 

You need some star dust and rustle up an east wind (Digikey)!
Max.