madmikejt12

hi, i have done a circuit with a 9v battery, a buzzer, an LDR and 2 transistors, when there is no light i want the buzzer to sound, i am using a lazer on one wall and an LDR on another and when the beam is broken, i want the buzzer to sound can you see anything wrong with this circuit?
Thanks, Mike

Attached Images

ldr.jpg (17.6 KB, 710 views)

madmikejt12

oops sorry, the circuit shows an LED not a buzzer but i plan to use a buzzer

Someone Electro

uhh...

This cirucit dosnet seem to be very functional to me.

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audioguru

Here is how to turn-on a transistor or darlington-connected pair. Match R1 to the value of your LDR. The little 9V battery won't last very long if the LDR and R1 are low resistance or if the LED or buzzer are continuously activated.

Attached Images

led_and_buzzer.png (34.9 KB, 689 views)

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Uncle $crooge

madmikejt12

should this be what resistance i want the buzzer to come on at?

Someone Electro

The R1 determins the sensetivety of it.

If its low resiatance then the bzer will start even in dim light if its high then the buzer will need to be im a darker place to start.

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madmikejt12

done it, it works, Thanks

audioguru

Horray! :lol: :lol:

Attached Images

icon_party3_205.gif (6.3 KB, 667 views)

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Uncle $crooge

Someone Electro

LOL :lol:

We at electroetch garante it to work.

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madmikejt12

worked a carm, set it up, leftt my room untidy, went out and my mum opened the door slightly BZZZZZZZZZZZZZZZZZZZZZZZZZZ she shut it and wouldnt go in again!!!!! :lol:

mstechca

LMAO not for advanced circuits, especially those coming from me.

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akg

what's that LMAO ??

madmikejt12

mine only work on breadboard, when i solder them, they never seem to work, i check all the tracks and nothing is touching things they shouldnt be, so i give up on them!!!

but, i have got ONE project to work, an adjustable LED flasher using a 555

audioguru

Don't give up.
1) Look at whether the emitter and collector of the transistors are reversed. A good pic of the pins of a transistor is shown in its datasheet.
2) Maybe your soldering iron is too hot or too dirty. My temperature-controlled soldering iron tip is cleaned by a quick wipe on a damp sponge then makes a perfect solder joint in 1 second.
3) Use rosin-cored solder. :lol:

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madmikejt12

i mean soldering circuits with no transistors, just diodes (which i checked and are the right way round), resistors, switches, a 555 etc