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30-minute Kitchen Timer

2017-11-27 20:46  
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30 minute Kitchen Timer circuit 300x253

Here is a kitchen need built around CD 4060. Often it so happens that the housewife forgets some thing left on the hot stove or in the washing machine as she watches TV or she talks to a friend over a neighborhood fence or she just wants to try a new recipe requiring a finite time. This is a timely personal reminder which gives an alarm, say after 30 minutes, or any other preset time. It can also work as a clock for the students who appear for the competitive exams.

The circuit is shown in Schematic 20. Again CD 4060 is used, a 14 stage divider oscillator IC. Oscillator frequency is set by the components at Pins 9,10,11. Frequency can also be adjusted using variable resistance Rl. With the components shown an alarm can be adjusted for 30 minutes at the output. Outputs at Q14 at Pin 3 and out put Q13 at Pin 2 are connected to the two terminals of SPST switch S2. Q14 gives 16384 divisions and Q13 gives 8192 divisions.

Switch S2 selects any one of the outputs and connects to BC147 transistor. When the selected output goes high, the transistor drives two terminal piezo buzzer. It also clamps CD 4060 from further oscillation through D3. If Q14 is selected timing will be 30 minutes and when Q13 is selected the timing will be 15 minutes as adjusted by Rl. By using a multi pole single throw switch, other timings can be achieved. We can get division ratios of Q10 at pin 15, Q9 at pin 13 and Q8 at pin 14, which can be used appropriately. Use musical buzzer to give a pleasant sound in the kitchen.

Flashing LED at Q3 is incorporated to indicate the activity of the IC. S1 is the reset switch. When SI is pressed even momentarily, Pin 12 goes high, it resets all counters and oscillator starts allover again.

Construction is straightforward and this IC is a CMOS device. Construction on a Vero board should do well. A simple full wave supply of 12V would suffice. During trials keep the output buzzer at Q10, or Ql 1. It gives lesser divisions and correspondingly less time cycle of operation. It is tedious to wait for half an hour to check the operation of the circuit during trials. This makes for a faster adjustment cycle time.

Other timings can be achieved by manipulating components at 9,10, and 11 with the formula given earlier. As the basic frequency is divided a number of times, accuracy is better even if the time delay is in the order of few hours. 555 cannot achieve this accuracy easily.


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