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Increasing the volume level of an alarm over a time period!

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Shez

New Member
Hi guys,

Not sure if anyone can help me but I am wanting to build an alarm clock whereby the alarm will begin to sound about 10 minutes before the user will get up. The user will set the time on the clock and then 10 minutes before this time the alarm will begin to sound.

The thing is I want the sound to automatically increase in volume during this period, i.e it starts off fairly quietly and get louder over the 10 minute period. I would also like it to have a snooze button that will silence it for 3 minutes each time it is pressed.

Does anyone know of any circuit diagrams that would show me how to do this?? Or has anyone got any diagrams of a circuit that would do this?

Many thanks :wink:
Shez
 

crust

Member
What kind of sound do you want? It is fairly easy to build an oscillator and use an opamp to drive a speaker. Then I suppose you could just vary the amount of amplification. However, since you need to use some type logic to control the clock/alarm/snooze functions, I would synthesize whatever audio wave I wanted in software and output that wave through a cheap DAC or ladder network to a 386 amp to a speaker. Then adjusting the volume is as simple as dividing your synthesized signal in software (by right shifting). The output rate of your signal controls the frequency of your oscillation. Then the snooze/display/alarm function are straightforward. You could derive the 60Hz time base from either a watch crystal or the power line (dont hook it up directly) -- It is fairly well regulated for long term accuracy.
 

Shez

New Member
Hi,
I'm wanting to use an ISD chip that will have various recorded sounds on, I also want to be able to switch between these sounds and have a standard type buzzer sound as well.

Cheers
Shez 8)
 

Electric Rain

New Member
Well, you could use a motorized pot for the volume control, and have it running very slow to span the 10 mins. That's really all I can help you with, I don't know enough to help you very much with anything else. But I do know that All Electronics Corp. has motorized pots. :wink: Hope this helps!

Rain
 

crust

Member
You can build or buy a voltage controlled amplifier which adjusts the gain based on a voltage applied to a control pin. One such part is the Burr-Brown VCA610. This part is a wideband amp, but there are probably some for audio applications. Then you can feed a driver to run your speaker.
 
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