View Full Version : A temporary closed switch circuit

01-30-2010, 01:51 PM
Hey all. I'm not sure if this is the right place to put this or not, but it's not exactly robot related so here goes...

I have a project that is this: A small treasure chest has a dismantled toy sound recorder stored in it's bottom. The play button is wired to a normally closed switch such that when the box is opened, the switch is no longer depressed and thus closed, thereby triggering the sound from the recorder (In this case, the 'you got an item' jingle from the Zelda games.)

My problem is that as long as the play button on this particular toy is held down, the sound repeats... I'd like it to play once, rather than looping while the chest is open. I could probably easily solve this problem with an atmega, but I haven't programmed them in forever and the only ones I have left are 168's from my arduino boards. This seems like over kill and waste of a chip that could be used for something more powerful, but I don't know enough about electronic circuits to think of something simpler.

So... does anyone have any suggestions for a simple circuit that would only allow the circuit to be closed for a few ms? The timing doesn't have to be super precise, it just has to open the circuit again before the sound repeats.

Thanks for taking the time to read


01-30-2010, 02:20 PM
Look at a 555 timer. It should just take a few parts to do what you want to do.

01-30-2010, 03:25 PM
If you don't mind the sound also playing when the box is closed. A sliding bar with a hump attached to the lid that trips a limit switch when the hump passes by might be an option. Even simpler would be to have a bare wire attached to the lid edge and a small metal piece on the chest where they momentarly touch when the lid is opened. A little more complex, but something similar probably can be done for a single play.

01-30-2010, 03:44 PM
Yeah, I'd though about having some kind of physical temporary contact mechanism, but I think I'd rather go a circuit route, to avoid having it play again when it closes. I've never used a 555 timer, but I know they're very popular. I will look into it. Thanks.

01-30-2010, 08:24 PM
Just thinking about the double play issue, a setup for single play would be easy. Use a thin piece of flexable plastic horozontally mounted with the bare end of one wire glued to the bottom, with the bare end of the other wire moving up and down against it at a horozontal 90 deg to the plastic mounted wire as the lid is opened and closed. When the lid is opened the horozontal wire moves upward brushing against the bottom of the plastic with the mounted wire, making contact as it bends the plastic mount upward and moves past. Momentary contact is made between the two wires. When the lid is closed the horozontal wire moves down bending the plastic downward as it passes by. Contact is not made as the wire mounted on the bottom of the piece of plastic is not touched by the moving wire during downward movement. Just a possible simple alternative to a more involved electronic solution. :wink:

01-30-2010, 11:05 PM
Ah. I see what you mean. That's not a bad idea at all. But my chest is pretty small, so I can only assume that if I tried to make something like that it would end up looking rather cumbersome compared to the rest of the box (since I am terrible at working with physical materials @[email protected]). Still, definitely a cool solution.

01-31-2010, 01:13 PM
This (http://www.ecelab.com/circuit-monostable-555.htm) should do the trick just fine, as Jes pointed out