[ale] OT: Two for the EE and hobbyests

[Jim]

I'd go with a simple microcomputer development system like the basic 
stamp.  I'd front end it with a LM-380 and a cheap mike located next to 
the howling rock for simplicity in hookup.  That way you'd have both the 
sound and sight effects. Timing is a snap with the microcontroller.  A 
cheap relay could be interfaced via a transistor to turn the smoke 
on/off.  That option would be the simplest to implement, but more 
expensive, I think the basic stamp dev kit can be had for around $100 or 
less. 

If you want a hardware solution.  I'd imagine the same input via the 
LM-380 going to a comparator (op amp) to set an S/R flipflop which turns 
on timer consisting of a 555 chip followed by the same transistor/relay 
as in the first solution.  The interface between the op amp and the 
flipflop could be routed through an AND gate (or NAND)  with the second 
input as the output of a second 555 timer that gets triggered at the 
same time as the first one, however it is set to time out after 30+45 
seconds.  The idea being that this second timer would disable the AND 
gate so no more intput from the rock would arrive to kick off the first 
timer until 75 seconds elapses.    Long delays are sometimes hard to get 
with 555 timer, so often a 4017 cmos counter is used to extend the 
time.  For instance to get a 75 second delay from a 555 you'd need a one 
meg resistor and a 750 microfarad capacitor.  750 microfarad caps are 
hard to come by, so you'd have to go to a 1000.  Now you're getting into 
an unstable range.  I'd probably opt for the 4017 at $0.39 from jameco 
and more like a 250 microfarad and a 30k resistor to get a delay of 7.5 
seconds.  Then if you divide by 10 you get your 75 seconds.  A 120 K and 
250 microF cap will get your the 30 seconds.  Probably better to use a 
variable resistor of some value over what you need and fine tune it for 
better precision.

Get a breadboard from somewhere if you don't have one already.  Most of 
these parts are probably available from Fry's but I'm sure Jameco and 
other parts houses have them too.

Jim.




Robert L. Harris wrote:
>   Well, in setting up for Halloween I have two little projects I want to
> accomplish.  First, I have a fogger with the extended cord with a button
> for triggering the fog.  Last year I had it on an X10 to control the
> power via a Linux Cron and just clamped down the button so it would spray
> when the power was on.  This year I'm thinking I'd like to remove the
> button and hook it up to a motion sensor, something like from one of
> those cheesy rocks that howl when you get two close.  I figure that
> would be easy enough, but I am thinking I'd like it to run for 30
> seconds, then stay off for 45 seconds or such so my house doesn't fill
> up with Fog.   Has anyone built something like this?
>
>   Second, I have a bright red light I'd like to put on a timed dimmer so
> the light would pulse on and off in window'd hallway over the front
> door.  Anyone have any ideas on something other than a cron'd X10 that
> would slowly dim in and out?
>
> Yes, I like Halloween...
>   Robert
>