This is a Dark Detector circuit that utilizes 1) the astable ocillator that you can make with a 555 to drive a piezo and 2) the reset threshold of the chip.
Credits to Tony van Roon for the circuit diagram.
I'm planning to either
1) combine it with a strobe light so with each "off" cycle, it screeches or
2) Put it over the doorbell (so it can be used seasonally too! : ] )
Step 1: Step One: Gather the Parts
555 Timer IC (I used a Texas Instruments NE555P, you can use pretty much any other brand)
A breadboard (doesn't have to be big)
Some wire; bare or stripped (you can use staples if they are thin enough)
One 1 megaohm resistor
One 100K resistor
One 100 ohm resistor (a 100 ohm potentiometer is better but optional)
One 1000 picofarad capacitor (in nanofarads: 1 nF in microfarads: .001 uF)
A Cds cell
A Piezo siren/buzzer
The resistor values can be experimented with but I reccomend these values for the most sucess.
The piezo can also be a speaker.
The capacitor value should probably stay the same.
You can try different Cds cells.
A great place to find components is the Electronic Goldmine: http://www.goldmine-elec.com
Step 2: Step Two: Put the Timer In
Step 3: Step Three: Stick the Negative and Positive Rails In.
Connect the 1st pin with the negative rail.
Then, connect the 8th pin with the positive rail.
If you need help with the pinouts, see the Pin Diagram picture.
Step 4: Step Four: Connect Pins 2 and 6...
Step 5: Step Five: Stick (yes Stick) the 100k Resistor In
Step 6: Step 6: Put (not Stick) the 1 Megaohm Resistor in It's Place
Step 7: Step Seven: Stick the Capacitor In
Step 8: Step Eight: Put the Cds Cell In
Step 9: Step Nine: the Hard Part (for Some)
Look carefully at the picture. If that doesn't help, read below
_The Hard Part_
Take a piece of wire long enough to span about 5 to 6 breaboard-cells (if anyone knows the term, please tell me). Stick it to the 3rd pin. Stick the other side to an adjacent area in the board.
Now, take the piezo's postive lead and stick it in the adjacent cubicle. Stick the negative wire into the negative rail. Now, put the potentiometer in. the first lead goes into the into the same row as the wire. The middle lead goes into the column with the positive piezo.
Now, connect a fresh nine volt battery to the correct rails.
Thats it! You're done.
Step 10: Troubleshooting, Shooting Trouble, Et Omnis
If you have any problems, look over all of the steps.
Make sure that you put the wires into the correct pins-rows. When I first made this circuit, I put the Cds cell into pin 3 and pin 1 when it was actually pin 4 and pin 1.
Another problem could be that some of your wire/leads are touching/shorting. Make sure that the only thing the leads touch are the breadboard cubicles.
Maybe your components are broken. The 555 is very sensitive to static electricity.
Also, USE A NINE VOLT BATTERY! Alkalines are the best but rechargables will work. I used a power supply.
If you've tried the above and still can't get the circuit to work, drop me a comment and I'll see what I can do.
I hope you've enjoyed creating a Dark Detector. Some possible next steps are:
Puting it in an altoids tin (of course!)
Puting it in a McDonalds apple pie box (what I'm going to do)
Experimenting with different reisistor values.