portable egg timer

portable egg timer Packing a rucksack to go camping always poses problems. Either you pack everything exept the kitchen sink and stagger under the weight, or you keep the weight down but find yourself without something essential. An egg timer is not absol- utely essential, of course, but it is often very handy. This circuit is aimed at people who want a small, battery-powered timer, which could also be used at home, if you don"t have a mains socket free for an electronic egg timer. One half of the 556 timer is used to sound the buzzer. It is connected as an astable multivibrator and oscillates at about 2 kHz. The actual S3 bi )KO 2720 81 timing is controlled by the other half of the timer. The sequence starts when S3 connects the trigger input of the IC to ground. The length of the timing pulse is determined by the Pl/R3/C network. For the prototype, C consisted of seven 47μF/6 V capacitors in parallel. The total capacitance, about 300 μF, gives a time of 61/2 minutes with Pijn ...