Musical alarm timer circuit
The circuit is built around popular CMOS oscillator/divider CD4060 (IC1). It works off a 9V PP3 battery and its standby current drain is very low.
By adjusting preset VR1, the time delay can be adjusted. After time delay is over, output pin 3 of IC1 goes high and npn transistor T1 conducts to provide positive power supply to melody generator IC UM66 (IC2) at its pin 2. Zener diode ZD1 reduces this power supply to 3.3V required for operation of IC2.
The output of IC2 is fed to the loudspeaker (LS1) via driver transistor T1. Preset VR2 is used to control the volume of the loudspeaker.
The timer gets activated when power is supplied by pressing switch S1. To switch off the alarm, you need to switch off the power supply.
The article was first published in October 2004 and has recently been updated.