Inexpensive clock radios do not have separate slumber and wake-up volume settings. However, with a small, easily fitted circuit you can go to sleep with quiet music and still be sure of waking up on time. This is achieved without the cumbersome fitting of a second potentiometer. Instead, the circuit boosts the volume level somewhat relative to the set level. For this purpose, the ground lead of the volume pot is
opened and a trimpot is inserted. The setting of this trimpot is a matter of personal taste and also depends on the setting of the ‘real’ volume pot. As a general rule, you should use around one-quarter of the setting of the original pot. A transistor is connected in parallel with P1 in order to short-circuit the trimpot and thus guarantee that The volume can be fully reduced to zero. Both of the additional components should be soldered directly to the original post for better hum suppression.
An R-S flip-flop made from AND gates and delay networks are used to control the transistor. The flip-flop (IC1a and IC1b) is set with a High level at the output of IC1a by a Low pulse from RC network R2/C2. The signal from IC1a reaches the two inputs of IC1c after being delayed by R3 and C3. If both of these inputs are High, IC1c cuts off the transistor. Due to the time delay, the wake-up music begins at the reduced volume level and then changes to the set level when the time delay
expires. The volume level can be reduced manually by pressing reset switch S1, which pulls the input of gate IC1b Low and causes the R-S flip-flop to toggle to the opposite state.
The bistable stage remains in this state until the supply voltage is switched off.
