If you want revenge that won’t kill someone, just make them go insane, have I got the thing for you!! I whipped this device up over the last couple of days and couldnt be more satisfied :lol:

Place this in a room where somebody sleeps. While the light is on, this circuit will not make a peep. When the light turns off though, the circuit will stay quiet for about 10 seconds (determined by the 1000uf cap and the 22k resistor) and then turn on. When they hear it, they will get up and turn on the light to look for it, but of course it will turn off. Thinking that they are imagining things, they will turn off the light and go back to bed. 10 seconds later, they will hear it . . . it’s a vicious cycle :twisted:

How it works: When the LDR senses light, it turns Q1 on, which in turn makes Q2’s base more negative than positive: transistor (and buzzer) is off. When the LDR senses no light, it turns Q1 off. The capacitor discharges through the 22k resistor, all the while causing Q2’s base more negative than positive (the 10 sec delay). When it is done discharging, the 22k resistor biases the base of Q2 positively, which turns the transistor and the buzzer on. Simple as that :lol:

To make a longer delay, just increase the capacitance. Since the 22k resistor serves a dual purpose: draining the capacitor and biasing Q2, it should not be made a higher value to increase the length of the delay because it then won’t be able to bias Q2 correctly. Of course you can experiment. I think that the value can be increased a bit more. If you want to shorten the delay, by all means, decrease the value of that resistor, just as long as the value is so low that Q2 will receive too much current through the base and damage it. I’m not sure if this will happen with so low a supply voltage, but beter 2 be safe than sorry.

The 5k POT and the 2.2k resistor in series with it work very well with the 3-16 volt buzzer. If it is a small room, lowering the value of the POT will make the buzzer quieter and harder to find. If you use a different buzzer, you will just have to experiment to find the right value of resistor(s). Just make sure that you turn the buzzer WAAAY down to where u can barely hear it, that way, they will have a very hard time finding it.

Any small small signal NPN transistor will work for NPNs in the circuit, i personally used 2n3904's cuz i have a ton of them, but like i said, anything will work.

This circuit is EXTREMELY sensitive to light. Just turning on a flashlight in the room will turn it off.

If requested, I will provide a PCB, although u will have to make sure that the capacitor, the POT, and the buzzer will fit on it.

Have fun . . . and don’t be too cruel :cry:

Attached Thumbnails

 

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what transistors ave you used in this ciruit

 

Any small signal/general purpose NPN transistors will do, eg 2N2222, BC547/8/9, 2N3904, PN100 etc etc

 

I used something similar a long time ago.....
It was something that resembled a cricket singing, and was triggered by the lack of light.....some 50...55 seconds after your target switched the lights off...
I really enjoyed annoying my older sister , when she was in her bedroom with her boyfriend.....
Such an evil boy I was!!!!
:twisted:

 

and still are i'm sure :lol:

What's really good is to put a bug in the room and listen to the person cursing and swearing :twisted:

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this is a cool circuit though it is too sensitive to light. you should try making a similar circuit using an lm339 op amp. that way you could adjust the sensitivity easier. just a thought

 

That's true, If you want to make it less sensitive to light, do this:

Add a resistor from the base of Q1 to ground. This will make the base of Q1 not be so positive. Try 100k, and then go up or down from there.

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instead of keep changing resistors why not use avarible resistor :?: :twisted:

 

good point :lol: . my way works fine for me because i only want it to work when it is totally dark, but if you want to change the darkness level that it activates at, do so!!

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Eh Zac,
Thats a wicked little circuit mate, time for me to make one up as the family's gone out for the day and when my son goes to bed tonite :twisted: we can say he's just hearing things in his head. Although when my missus finds out I reckon I'll break the 3 minute mile just running away.

Cheers Bryan1

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lol, its a ball aint it? just make sure that you test it out yourself in total silence first because when there is total silence, it seems it can be heard everywhere in the house, whereas even with a little background noise, at the same level of volume, you can barely hear it.

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thats extremely cool. im going to make that when i get home from school today. another ideal i have is put a potentiometer in series with the buzzer to control volume, and maybe an op amp behind that to amplify it so the backgrownd noise wont drown it out. just a thought.

 

meaby this thing cod be made smarter whith an PIC to make it bepp random or the faster the light gets thurned on the longer the delay so wen the guy gets frustrated and is wating at the light switch it will make a long intraval but wen he only cheks it out and gown to bed then it wod beep fast.

This wod make it even more frustrating!

Or even to make it work at 25 kHz so it wod make the dogs go nuts and start barking the guy wod go to the window to make the dog shut up and wen he gets back in bed and thurns the light off,it makes the beep and the dog if off agen so this cicle wod cotinue until the guy goes completly insane (or the dog since since beeps ower 20kHz drive them nuts).This way he proboly wodnt figureit out tha an litle device the cousing it.

I think once a guy on this forums told that he instaled an litle device in the refirgeraor that started beeping wen it senced light(wen you open the firge) and in the midle of the night his mom tryed to get an snack and was realy frightend form the siden bepping and he had to "disarm" it in the midle of the night.

Piezo lighters are good for pranks too.

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hmm, good ideas dust and electro :twisted:

ive been thinking about somehow upgrading this thing. it would give me a good chance to work with PICs. i would like to get some experience with them :lol:

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well first you need an PIC (you cod get free smaples form microchip) then you need an programer(I made is my self out of wery litle parts)to get your program in to it and some other component like 5V regulators (PIC need an wery clean power suply),crystals(to set the clock)

I have 2 PIC16F88 and 2 PIC18F252

i fot the PIC18F252 in smd pakege so i dont have much use for it and the pogramidosent suport it. but the PIC16F88 works fine

the cheapet PICs are half a dolar but these dont have much fetures and there are PICs for 10$ that have all kinds of goodys.Its a realy cheap cumputer on an chip.Most of them run at max 20 MHz and some rum up to 48 MHz

i program them in mikroBasic becose it the easyest porgraming languge to lern (I allredy programed in VisualBacic and Basic is wery silamer to it)

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