Picture of
Circuits for the Hobbyist.bmp
Well, this is my first instructable (yay) so, here it goes!

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.

For Halloween:
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

Picture of 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
rishi19933 years ago
buzzer sounds when i move potentiometer knob whether it is dark or light.
what i have to do
adjust potentiometer accordingly, as it controls the sensitivity of light. you can use this for setting the device according to your lighting in house or any other place.
cheche124 years ago
is it ok if i replace the buzzer with an LED??? how many LED can i put on it??/
rsingh98 cheche125 months ago
at least 2 LEDs, in series.
aya.elsbaie8 months ago

لو سمحتوا انا عملت نفس الخطوات بس طلعت معكوسه الbuzzerبيطلع صوت والنور شغال

buzzer sounds whether it is light or dark......yyy??
bhagavathy2 years ago
hello, the circuit worked,but need the explanation & design of the circuit
kansari4 years ago
my projct is automtic street light,same as dark detector,i make some changes in circuit,it runs perfectly.in my circuit
1:pin 1 ground.
2:pin 2 connected with capacitor which is grounded also it also short with pin 6 and connected with one end of potentio meter,pin 7 with other end of potentio meter
3:one leg of ldr connected with ground and othr goes in pin 4 which is reset
pin 3 is output pin.
but matter is i cant understand the function of reset pin,please explain me in digital\logic lang.
kansari4 years ago
i want to know how in this circuit reset pin works?
jashshah4 years ago
can u please explain how this circuit works?????
coleyy4 years ago
what are the codes for a 1m resistor and a 0.001uf mylar capacitor
BSN4_N4 years ago
WHere does the 3rd lead go ? and which wire does the first lead of the potentiometer go?
dandeeman (author)  BSN4_N4 years ago
The 3rd lead is NC (not connected.) The lead that is pointing out (the center lead) is connected to the red piezo wire.
amorarun5 years ago
Instead of a piezo will a relay work. I need a dark detecting circuit which could turn on/off a relay. I tried some other circuits but I failed don't know where I went wrong.
hackman885 years ago
I also using 555ic For Dark Detector i Haven't tried This Try using Rely For other Function its Cool Ill GIve you My Schematic For that Itseasy to Troubleshoot...
Zem5 years ago
 Second and sixth? Looks like 8th and 4th to me.
dandeeman (author)  Zem5 years ago
Oops! Fixed. Thank you, swamp mattress of Squornshellous Zeta : ]
Zem dandeeman5 years ago
 No prob =)
I was wondering if there is a way to make this give a double beep, a second of silence and then a double beep again? Like you would normally here a cricket do.. and without an audrino...
oweng40005 years ago
et omnis?
dandeeman (author)  oweng40005 years ago

Et omnis as in "the page should cover all problems" which unfortunately, it doesn't, as evidenced by many of the comments.

Gotta get those latin phrases down!

oweng40005 years ago
if i bumped up the capacitence and changed out the buzzer for an led what would happen? an Led flasher that would shut it self off constantly?
dandeeman (author)  oweng40005 years ago
The capacitance dictates the sensitivity of the CDS cell; the buzzer is driven at roughly 100 - 5000 Hz.

So, when the capacitor value is increased and the buzzer is replaced with an led and the light threshold of the circuit is reached, the led would ocsillate at the same frequency that the buzzer would (ie about 100 - 5000 Hz)

Though I'm not entirely sure, I am fairly certain that above is what would happen.

Hoped that answered your question!
koolariz5 years ago
what's the output of your schematic?
could it drive a BLUE led? with a smaller voltage supply?
dandeeman (author)  koolariz5 years ago

The output of the circuit is pretty much the same voltage that you pump into it. Generally, blue leds can be run at about 4.5 volts DC.

The 555 has a voltage range of 4.5 volts to 15 volts, more than enough to drive a blue led.

Hope that answered your question!

Well formatted..! And a very good instructable for beginners' electronics! And a circuit diagram is needed! :)
dandeeman (author)  Smokedasphalt6 years ago
Ok, I just added the circuit diagram. Thanks for the comments!
Oh, come on! You've copied the circuit diagram from Tony van Roon's website!!
Atleast mention him in the instructable!
dandeeman (author)  Smokedasphalt6 years ago
Tony van Roon? I found this in a PDF file called "Electronics for the Hobbyist." I guess it came from him though so I'll put him in the instructable. Thank you for the feed back though.
No problem! :)
hominid6 years ago
Very nice and well constructed, but could I be a pain and ask for the circuit diagram? Thank you, Steve.
dandeeman (author)  hominid6 years ago
I added the diagram but... "Steve"?