Introduction: "Dark Detector" Using a 555 Timer IC

Picture of "Dark Detector" Using a 555 Timer IC

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:

Step 2: Step Two: Put the Timer In

Picture of Step Two: Put the Timer In

Stick the timer in the breadboard so that the notch and/or circle is facing to the left.

Step 3: Step Three: Stick the Negative and Positive Rails In.

Picture of Step Three: Stick the Negative and Positive Rails In.

If you haven't worked with circuits before, here comes the (semi) tricky part.
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...

Picture of Step Four: Connect Pins 2 and 6...

...with a piece of wire. Again, if you need help identifying the pins, consult the pin chart.

Step 5: Step Five: Stick (yes Stick) the 100k Resistor In

Picture of Step Five: Stick (yes Stick) the 100k Resistor In

Connect the 4th and 8th pin with it.

Step 6: Step 6: Put (not Stick) the 1 Megaohm Resistor in It's Place

Picture of Step 6: Put (not Stick) the 1 Megaohm Resistor in It's Place

It's place would be connecting the 2nd pin to the 3rd pin.

Step 7: Step Seven: Stick the Capacitor In

Picture of Step Seven: Stick the Capacitor In

Put it in pins one and two. If you have an electrolytic capacitor, make sure that the polarity is correct.

Step 8: Step Eight: Put the Cds Cell In

Picture of Step Eight: Put the Cds Cell In

Make sure that it connects pin 1 and pin 4.

Step 9: Step Nine: the Hard Part (for Some)

Picture of Step Nine: the Hard Part (for Some)

Well, you've gotten this far. So, pat yourself on the back and get ready.

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

Picture of 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.



GauravR22 (author)2016-01-29

ane piche bhar lo ppt.......

ShashwatVerma2273 (author)2015-09-02

i cant get the parts required online and if i get some it says that its not available in india or says cash on delivery is not available

what should i do now?

rishi1993 (author)2012-07-16

buzzer sounds when i move potentiometer knob whether it is dark or light.
what i have to do

rsingh98 (author)rishi19932015-03-17

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.

cheche12 (author)2010-11-06

is it ok if i replace the buzzer with an LED??? how many LED can i put on it??/

rsingh98 (author)cheche122015-03-17

at least 2 LEDs, in series.

aya.elsbaie (author)2014-12-15

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

shaikmdsohail94 (author)2013-04-20

buzzer sounds whether it is light or dark......yyy??

bhagavathy (author)2013-04-08

hello, the circuit worked,but need the explanation & design of the circuit

kansari (author)2011-05-07

my projct is automtic street light,same as dark detector,i make some changes in circuit,it runs 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 (author)2011-05-07

i want to know how in this circuit reset pin works?

jashshah (author)2011-04-30

can u please explain how this circuit works?????

coleyy (author)2010-12-26

what are the codes for a 1m resistor and a 0.001uf mylar capacitor

BSN4_N (author)2010-10-22

WHere does the 3rd lead go ? and which wire does the first lead of the potentiometer go?

dandeeman (author)BSN4_N2010-10-22

The 3rd lead is NC (not connected.) The lead that is pointing out (the center lead) is connected to the red piezo wire.

amorarun (author)2010-08-23

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 (author)2010-08-05

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 (author)2010-03-11

 Second and sixth? Looks like 8th and 4th to me.

dandeeman (author)Zem2010-04-05

Oops! Fixed. Thank you, swamp mattress of Squornshellous Zeta : ]

Zem (author)dandeeman2010-04-05

 No prob =)

OnCrowsWings (author)2010-03-09

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 (author)2010-03-03

et omnis?

dandeeman (author)oweng40002010-03-05

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 (author)2010-03-03

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)oweng40002010-03-05

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!

koolariz (author)2010-01-18

what's the output of your schematic?
could it drive a BLUE led? with a smaller voltage supply?

dandeeman (author)koolariz2010-01-23

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!

Smokedasphalt (author)2009-08-31

Well formatted..! And a very good instructable for beginners' electronics! And a circuit diagram is needed! :)

dandeeman (author)Smokedasphalt2009-08-31

Ok, I just added the circuit diagram. Thanks for the comments!

Smokedasphalt (author)dandeeman2009-09-01

Oh, come on! You've copied the circuit diagram from Tony van Roon's website!!
Atleast mention him in the instructable!

dandeeman (author)Smokedasphalt2009-09-01

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.

Smokedasphalt (author)dandeeman2009-09-02

No problem! :)

hominid (author)2009-08-30

Very nice and well constructed, but could I be a pain and ask for the circuit diagram? Thank you, Steve.

dandeeman (author)hominid2009-08-31

I added the diagram but... "Steve"?

About This Instructable




Bio: I am currently a middle school student. I am primarily interested in the realms of computers and electronics, but I also enjoy playing the piano.
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