# "Dark Detector" using a 555 timer IC

10 Steps
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! :  ] )

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## Step 1: Step One: Gather the Parts

_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)
A Cds cell
A Piezo siren/buzzer

_Notes_
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
shaikmdsohail94 says: Apr 20, 2013. 10:43 AM
buzzer sounds whether it is light or dark......yyy??
bhagavathy says: Apr 8, 2013. 7:39 AM
hello, the circuit worked,but need the explanation & design of the circuit
rishi1993 says: Jul 16, 2012. 9:33 AM
buzzer sounds when i move potentiometer knob whether it is dark or light.
what i have to do
kansari says: May 7, 2011. 12:37 PM
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.
kansari says: May 7, 2011. 12:26 PM
i want to know how in this circuit reset pin works?
jashshah says: Apr 30, 2011. 11:58 PM
can u please explain how this circuit works?????
coleyy says: Dec 26, 2010. 6:38 PM
what are the codes for a 1m resistor and a 0.001uf mylar capacitor
cheche12 says: Nov 6, 2010. 10:40 PM
is it ok if i replace the buzzer with an LED??? how many LED can i put on it??/
BSN4_N says: Oct 22, 2010. 4:28 PM
WHere does the 3rd lead go ? and which wire does the first lead of the potentiometer go?
dandeeman (author) in reply to BSN4_NOct 22, 2010. 5:27 PM
The 3rd lead is NC (not connected.) The lead that is pointing out (the center lead) is connected to the red piezo wire.
amorarun says: Aug 23, 2010. 9:46 PM
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.
hackman88 says: Aug 5, 2010. 6:59 AM
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...
Zem says: Mar 11, 2010. 8:50 PM
Second and sixth? Looks like 8th and 4th to me.
dandeeman (author) in reply to ZemApr 5, 2010. 2:26 PM
Oops! Fixed. Thank you, swamp mattress of Squornshellous Zeta : ]
Zem in reply to dandeemanApr 5, 2010. 6:14 PM
No prob =)
OnCrowsWings says: Mar 9, 2010. 3:21 AM
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...
oweng4000 says: Mar 3, 2010. 11:20 AM
et omnis?
dandeeman (author) in reply to oweng4000Mar 5, 2010. 4:59 PM

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!

oweng4000 says: Mar 3, 2010. 8:58 AM
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) in reply to oweng4000Mar 5, 2010. 4:56 PM
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.

koolariz says: Jan 18, 2010. 6:34 PM
hey,
what's the output of your schematic?
could it drive a BLUE led? with a smaller voltage supply?
dandeeman (author) in reply to koolarizJan 23, 2010. 11:05 AM

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.

Smokedasphalt says: Aug 31, 2009. 2:34 AM
Well formatted..! And a very good instructable for beginners' electronics! And a circuit diagram is needed! :)
dandeeman (author) in reply to SmokedasphaltAug 31, 2009. 1:44 PM