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Time Delay Circuit

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Time Delay Circuit

Unread postAuthor: PVC Arsenal 17 » Tue Jul 29, 2008 2:58 pm

I don't know jack sh*t about electronics so I need some help.

I'm trying to find a way to buy or build (but preferably buy) something that would allow me to press a button and it will delay a few seconds before closing the circuit. This device would have to as small as possible.

I'm trying to make a pneumatic airsoft "bomb" using a solenoid. I want to be able to flip a switch and have it go off a few seconds later. Now how do I do that? I'm clueless when it comes to electronics.


Thanks!
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Unread postAuthor: jonnyboy » Tue Jul 29, 2008 3:14 pm

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Unread postAuthor: TurboSuper » Tue Jul 29, 2008 3:22 pm

Hrm, a resistor, capacitor, and a schmitt trigger should do it...gimme a few minutes to cook up a schematic.

Edit: This should work, I can't guarantee it.

Image

The 74HC14s come as 8 gates in a 16-pin chip, look up a datasheet to see how to wire them, you will only need two. There should also be a small resistor between the second gate and the transistor. Change the delay by using a bigger cap/resistor.

I'm not really sure if this is over your head or not...worse comes to worse find a storebought photo-flash delay circuit or something.
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Unread postAuthor: psycix » Wed Jul 30, 2008 1:08 pm

Besides electrical cicuits, you could also use something mechanical or use pressure.

Have the switch open up a small solenoid valve, allowing pressure to (slowly) seep into some kind of small chamber (use something to block the flow), then use a pressure switch (something that closes an electrical circuit as soon as the pressure rises above a certain amount). You could build your own pressure switch out of a small piston, a spring and some pieces of metal. When the pressure overcomes the spring force, the piston get pushed and the metal pieces touch, completing the circuit.
You can tweak the delay time by changing the blocking of the flow.
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Unread postAuthor: jimmy101 » Wed Jul 30, 2008 2:03 pm

If you are not comfortable with building something from scratch how about an ADJUSTABLE INTERVAL TIMER KIT for $10.

Hard to tell from the photo but it is probably based on a 555 timer chip. It includes a 3 Amp relay.
Image
Velleman # MK111. For intermittent operation of circuits and equipment. Use for blinking light control, slide projector control etc. Pulse time adjustable between 0.5 and 5 seconds. Pause time adjustable between 2.5 and 60 seconds. 3 Amp output relay. Power supply 12-15 Vdc @ 100 mA (not included).


This will probably end up being cheaper than building one from scratch.
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Unread postAuthor: TurboSuper » Thu Jul 31, 2008 5:34 am

psycix wrote:Besides electrical cicuits, you could also use something mechanical or use pressure.


Or mabye a hybrid of both...use a wind up clock, rig electrodes to it's alarm system :D

Accurate delays up to 12 hours, plus the tick-tick-tick....
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