Small Circuits Revival (19): Alarm Clock Silencer

March 11, 2020 | 11:15
Small Circuits Revival (19): Alarm Clock Silencer
Small Circuits Revival (19): Alarm Clock Silencer

Alarm Clock Silencer – snooze with voice control

idea: Elex Team

People who jump out of bed, full of energy, to start the new day on the first sound of the alarm clock are few and far between. Most of us need a little time for the harsh reality to sink in and that is where the snooze button is really convenient: you can use it to silence the alarm clock for a few minutes.

The only problem, particularly when it is still dark in winter, is to find that button. This is usually done by groping around, with a high risk of the glass of water on the bedside table being knocked over, or worse...

There has to be a better way, and fortunately it's not difficult – take a look at the schematic of Figure 1. The heart of the circuit is an opamp (A1), which is configured as an inverting microphone amplifier. The microphone is an electret type which receives its required supply voltage via R1 and R2.

 
Figure 1.

The sensitivity of the amplifier is set with potentiometer P1. The output signal, via T3, drives an astable multivibrator (monostable) that is built from discrete parts using T1 and T2. The monostable time is determined by R9 and C4, and here that amounts to about half a second.

The remainder should be obvious: the monostable drives the relay used to close the contacts of the snooze button on the alarm clock. This will, of course, require a little bit of surgery to the alarm clock, but that should not present any difficulties to the dedicated tinkerer.

And a tip in closing: don't place the microphone too close to the loudspeaker of a radio – for obvious reasons. Whatever shout, cry, or expletive the sleeper utters when rudely torn from Morpheus's arms by the alarm clock sound, we leave entirely up to your imagination. And of course, this circuit is also suitable for a whole host of other applications!

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