This is for fun. How would you make a control system that causes the bathroom lights to flicker when when someone flushes the toilet?

I am thinking flow switch on the cold water supply to the tank piloting NO contacts on a relay. This relay feeds line voltage to a transformer (isolation type but tapped low) that causes an under voltage to the ballast at the fixture. (This of course assumes a fluorescent fixture). The under-driven ballast should now go in and out due to low voltage (think line flicker) if I am not mistaken. Even better if you have a magnetic and not electronic ballast. Flow switch opens again and lighting is normal.

Also, this is assuming that you love to change ballasts at your Moms house for a good laugh. Ideas? How to do it with incandescent fixtures?

Is it possible to have the lights dim in a varying manner according to the sound levels in the room?

Dave

I would probably use a commercially available wireless 3-way switch. I would tap into the switch of the battery powered stick-on with a sound trigger ckt. This would be hidden behind the tank.
Joe

Perhaps a set of wireless burglar alarm "contacts" in the tank, fastened in such a manner that hitting the flush will " trigger the wireless contact" and in return will send a signal to its receiver elsewhere, and from there control your light flicker circuit. Heck for laughs it can even momentarily sound a big 'ol bell! Wouldn't that be " alarming"
Figure that may be easier than plumbing in a flow switch, and best off, it will come out as easy as it went in when the joke is over.

A.D

maybe a low-voltage sound or liquid level detector circuit that could turn on or drive an amp that feeds into some white LEDs to supplement the existing lighting rather than interface with the AC.

I'm thinking a op amp as a level detector to go to full output, that would in turn activate a 555 timer circuit configured as an oscillator to drive the LEDs. I haven't done elctronics for fun in a long time - just safety these days. There's a lot of time between now and April 1st...

My son had a 'joke thing' fitted inside the toilet roll holder. When you pulled a sheet of paper, it emitted a loud & disgusting noise, at about 3.4 on the Richter Scale.
Ideal for embarassing unwanted visitors.
His wife put it in the trash.

The reason I mentioned the wireless 3-way is because the switch in the wall switching AC, will be a UL listed switch. I love circuit design as much or more as the next guy but hate L words like lawyer and liability.
Joe

You could use a hvac drain pan float switch mounted in the tank to initiate the flicker machine that you are engineering.

put a variable resistance transducer on the water line.

got a lot of iron in the water supply?

Wow this topic is getting a lot of help! Just goes to show what is important in life!
The noise detection idea would be pretty good as the lights would also dim when other noises were PASSED.

Am I missing something? Why is it that you want to do this? April is quite a while away....

Set up a relay to drop out (open) from a relay - put it far away enough that you wont hear it. And control that relay via a magnetic reed switch like those used for door contacts in alarm systems, and attach it to the bottom outside of the tank of the toilet. Then get a fairly strong magnet on a string hanging from the spindle between the lever and arm inside the toilet close to where the arm and lever come together. Set it up so the magnet has just barely enough strength to keep the switch closed, but will open on the slightest jarring of the string. As an electrician I would say to keep the control voltage as low as possible. When the toilet is flushed the magnet wil move and swing around in the tank just enough to shutter the relay and continue to do that until the currents of water stop after the tank fills. And if you are electronicaly inclined do something simular with an SCR control circuit instead with an even lower control voltage. Or use the red and blue lv conductors of a relay like this: http://www.wattstopper.com/getdoc/1224.pdf