Broadcast A/V alarm. Help with a 555 timing circuit.

Thread Starter

Quantum Flux

Joined Feb 19, 2010
18
Leave R2 where it was (2.2KΩ) and drop the capacitor to 10µF.

When the timer is idle that resistor is connected to ground through the chip.

If you want to reduce the current even more use a 1µF and 22KΩ. The math works the same for all values.

So, what did you find?
Will change the cap in the morning and check the timing.

I have just finished building 2 other 555 oscillators for the selectable tones (see render on first post). The circuits definitely work perfectly on their own but I'm not sure the best way to make the tone selectable. below is what i've drawn up based on my protoboard experiments. I've got a smooth wave, a square wave and a straight connection to V+ to give three different selectable sounds. Excuse the ass-about pin positions. It was just easier to draw and the software will see it just the same when it comes time to draw up the PCB.

EDIT: I will need to figure out a good way to amplify the output of the two 555 circuits as the volume on the piezo is significantly lower than when it's driven straight from power.

 
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Thread Starter

Quantum Flux

Joined Feb 19, 2010
18
adding resistance between the output and piezo to the 555 tone cct's just seems to decrease the frequency. Is there a way to decrease the volume?
 

Thread Starter

Quantum Flux

Joined Feb 19, 2010
18
Foam tape on the output? They really aren't meant to be quietened much.
when driven directly from power, adjusting the voltage seems to reduce or increase volume. I'm aiming for an adjustable volume. Check out the picture in the OP and you can see what i mean.

EDIT: i think i just came up with a solution. will try it now.
 
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