3 second fogger

Question

hello I'm new here and I have a question. I'm no electronics expert but what I'm trying to do I thought would be rather simple but I'm having trouble with one part hopefully somebody can help me.

I'm trying to put togther something for Haloween, what I've got is a doormat that says happy Haloween on it, I rigged it up so when it's stepped on it closes a circut, last year I used it to turn on a light. this year I want to use it so when it's stepped on it turns on my fogger for 3 seconds then stops until it's stepped on again. so that way I can put the doormat at the begining of my walkway and when someone steps on it the fogger I've placed about halfway up my walkway will shoot a 3 second burst of fog about knee high across the path they have to walk through to get to my door. like I said before it sounds simple and I've got everything else pretty much figured out but the 3 sec on time is harder than I thought. I need something that can activate when it receives a quick shot of low voltage dc from when the mat is stepped on and let low voltage dc flow through it for 3 seconds than shut off until it gets another shot from the mat. that way I can run lvdc through it to activate a relay that will switch on a 120 ac circuit for 3 seconds to run the fogger. so I guess what I kind of need is a relay that when it gets a quick shot of juice will only run for 3 sec then shut off until the next shot. now the only thing that HAS to be lvdc is the doormat part I don't want to run 120 ac through that part and risk shocking anyone.

can someone please help me?

Answer 1

Of the two mooted suggestions of 555 and Microcontroller, I'd personally opt for the microcontroller. It would allow you more control over exactly how to trigger the fogger.

For instance, stepping on the mat would trigger the fogger for 3 seconds - but what's to stop those pesky kids from jumping up and down on the mat to fog up the whole neighbourhood?

Using a microcontroller you could easily arrange it so that it won't re-trigger within, say, 30 seconds. You could also count how many steps per second there are, and if it determines that the kids are jumping on it to try and break your fogger it screams out a sound sample "Hey pesky kids! Git off mah proppertah! Or I'll set the dogs on yah!" (glorious redneck accent there by the way ;) )

BY the way, the Arduino may be your simplest option to get you going - simple to connect, program, and break ;)