# Project: Night Buzzer

Discussion in 'Electronic Projects' started by zachtheterrible, Jan 14, 2005.

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1. ### zachtheterribleActive Member

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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:

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2. ### rowleyNew Member

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what transistors ave you used in this ciruit

3. ### PhasorMember

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

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5. ### SmaugNew Member

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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:

6. ### zachtheterribleActive Member

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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:

7. ### barbuzzaaNew Member

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Insane

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

8. ### zachtheterribleActive Member

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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.

9. ### monkeytreeNew Member

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

10. ### zachtheterribleActive Member

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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!!

11. ### bryan1Well-Known Member

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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

12. ### zachtheterribleActive Member

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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.

13. ### dustinpruenteNew Member

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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.

14. ### Someone ElectroNew Member

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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.

15. ### zachtheterribleActive Member

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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:

16. ### Someone ElectroNew Member

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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)

17. ### zachtheterribleActive Member

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Im gonna have to do that someday. Not now, as you may have read ive got a rather large alarm project that im working on.

18. ### Someone ElectroNew Member

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Il try to make it since i have an PIC16F88,programer,5v regulator...

I suck together an perogramer out of a cumple of transistors and resitors and its on the LPT.The down side is i have to have an external power suply of 13v an 5V

anyway what do ou know about PICs?

Hmm...meaby an phototransistor on ADC and an piezo speker

19. ### Someone ElectroNew Member

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i got the hardware working but the damn phottotrasistos has 15° angle so it can only sence light of objects that is exsactly pinted it to (this wod be only useful in a shoting game there you have to point the "gun" directly in an LED)
I just cant find the photoresistor of mine wich has an 130° angle

Now i have to make the program (10 bit output from the ADC is casing me headaces becose 10 bit is harder to work whith than 8 bit )

First il try to make it work like the "analog original" works so your circuit will have an digital brother but then il try to complicate it a bit like the thiming thing.

wod be also cool to conect an microphone in but in not going to do that.

It also has an super small curent draw.Wean slilent it drawn 0.04 mA an that wod run on my litium cell for about 2 years continuestly by runing it at 34kHz(you beter not run it for that long since the guy may end up by the psycaetrist and if he finds out you cod end up in a hospital)
you can see an slight delay on the leds since it has to divide an 10 bit number whith 120 on such an low freqency (but i goes super smoth wen run at 10Mhz but then it draws 1.3mA)

how much dose your circuit draw?

20. ### zachtheterribleActive Member

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hey electro, thats a nice bit of information, glad youre keeping me informed.

I havent even checked what my circuit draws. at the time i built it, my ammeter was burned out. Dont ask about the stupidity that caused that.

What do I know about pics? Not a bloody thing. i am really going to investigate them though, i know there is so much that can be done with them.

what do you mean by that?

just short out the photoresistor while youre experimenting with it.

21. ### Someone ElectroNew Member

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Its working and it makes bzt evry so and so at 0.02 mA curent draw(whith 3.9V) it wod run 6 years on my 1150mAh litium cell! amazing!

and it ran a long time of an a cuple of caps i put on the power rails(2470uF to be exsact)

the mirophone wod betect if the guy starts yeling or an vibraon detrctor to detect the guy walking around the room

In the afternon il start maing it smarter

btw:
I fixed the phototransistor thing ba making it way more sesitive (that votage divider thing.you know)

we beter start sending each other PMs or lets get in a chat room somtine.