need some help in creating a light sensitive wakeup alarm...
already created a circuit(from the book electonics for dummies) but speaker isnt responding apart from a pop sound initially while giving connections
also iam not sure about speaker's rating...The circuits says a 8 ohm 1W speaker but nothing is marked in my speakers...

 

Hmm, that's not a lot to go on for someone to help troubleshoot.

- Can you post a schematic?
- Are you sure you wired everything properly?

Where did you get the speaker? Even if it's not an exact match, it should be doing something if your circuit is wired correctly. If it's way too big of a load, the output might be quiet, and if the speaker were undersized you might blow it, but if you're getting a pop when you connect it, the voice coil is still moving.

 

schematic is posted as an attachment please view guyz..

It doesnt say anything about values of photoresistors....what abt deir values..?

 

The circuit

IC1: LM555 Timer IC
_ Q1: 2N3906 PNP transistor
_ R1: 100K potentiometer
_ R2: 3.9 Kohm resistor
_ R3: 10 Kohm resistor
_ R4: 47 Kohm resistor
_ C1, C3: 0.01-⎧F disc (non-polarized) capacitor
_ C2: 1.0-⎧F electrolytic or tantalum (polarized) capacitor
_ Speaker: 8-ohm, 0.5-watt speaker

 

i have done everything as per the circuit...but its not giving any result...

 

If you connect a wire from pin 4 of 555 to pin 8, do you hear a tone?
What's the voltage on V+ ?

Allen

 

do u mean connecting 4 and 8(shorting them with a jumper) or is it as shown int he schematic....
i have applied 9v as the Vcc(using standard battery)

 

Yes. When pin 4 is at low voltage, the chip will not run. Connect pin 4 to +9 volts to put it in "run" mode.

 

ah...finally it worked...but iam hearing only a single freq sound, how can i change its freq...can anybody suggest any modifications in design..?

 

Replace R4 with a potentiometer wired as a rheostat (the center pin shorted to one of the end pins).

 

a pot cant we connect in the normal way...taking wires from one end pin and the middle pin...why short mid pin with one end pin?
and what ohm rating pot is to be used....can i get a police siren from this circuit...?

 

...why short mid pin with one end pin?

When the pot slider temporarily loses contact with the resistive material track, the circuit sees a suddenly very high "open" resistance. Connecting the slider to the opposite pole ensures that the maximum resistance in this situation is the nominal resistance of the pot. So connecting the opposite pole is a way to stabilize the output. Somewhat optional, but good form. Something you always do unless you have a reason not to.

 

There are only 2 places that R4 connects to. Where would you connect the third terminal of a potentiometer?

The pot would be labeled as 50 K ohms to replace the 47 K ohm R4.

No, this is not a police siren design. That would require another 555 chip to make a controller for this single frequency oscillator design.

 

thank u guys for the reply...
is it necessary that all terminals of pot shud be employed cant we use 1 end pin and i mid pin....and there isnt any sliding arrangement in pots...now did u mean a rheostat?

 

..is it necessary that all terminals of pot shud be employed cant we use 1 end pin and i mid pin...

You can. I said the technique of using all 3 is optional.

.and there isnt any sliding arrangement in pots...

And just how do you think they work?

 

Two Hall effect sensors detect the position of the adjustable magnetic shaft and a microprocessor outputs a resistance value.