This multipurpose timer circuit will give you alarm after every specific interval of time. You can also vary the time interval with the help of VR1. This timer can be used in kitchen. As many of us have habit to forget, to switch off button of gas, electric oven which lead to wastage of resources and your hard work. Now with the help of this circuit you will receive an alarm after specific time so that you can remember to off the device. Some other features of the circuit are:
1. You can also use it as alarm to switch off the motor because while watching TV or talking over phone we forget to switch off the pump in that case also it will give an alarm.
2. This circuit will engage the alarm after set period of time until you switch off the circuit.
3. It will provide you a melodious sound so it will not irritate your ears.
4. It works off a 9V PP3 battery and its stand by current is also very low.
Fig. 1: Prototype Of Multipurpose Timer Circuit On Breadboard
Fig. 2: Prototype Of Multipurpose Timer Circuit On Breadboard
The circuit is built around two IC namely CD4060 and UM66 with few more components. IC CD4060 is 14 stage ripple carry binary counter, divider and an oscillator. Its built in oscillator is main feature of this IC that’s why it can be used in numerous application like flasher, clock generator in timer circuits.
UM66 is a melody generator IC. In place of UM66 you can also use UM3561 which will produce different sound.
Here, IC1 is working as frequency dividing circuit. Its inbuilt oscillator is based on three inverters. The basic frequency of the internal oscillator is determined by the value of the capacitor connected to its pin 9 and the resistor connected to pin 10. By increasing or decreasing the value of capacitor and resistor, we can change the time period for which alarm remain “on” and “off”.
Internally the oscillator signal is applied to the first bistable which drives the second bistable and so on. Since each bistable divides its input signal by two, a total of fifteen signals are available, each of half the frequency of the previous one. Output Qn is the nth stage of the counter, representing 2n, for example Q4 is 24 = 16 (1/16 of clock frequency) and Q14 is 214 = 16384 (1/16384 of clock frequency). Note that Q1-3 and Q11 are not available
With the components shown in circuit diagram, you can adjust the alarm time from 30 seconds to 2minutes. This means that after every 30 sec to 2 minutes, you will receive a melodious sound. If you want to increase it up to 20 minutes just change the value of capacitor to 10uF and vary the VR1 to set the time.
When power supply is given to circuit, the pulse at the junction R1 and C2 resets the counter and counting starts.
And when counter reaches bit 8192(Q9), pin 13 goes high and transistor conducts to provide positive supply to melody generator IC UM66 at its pin2. We have used zener diode to regulate the power supply to 3.3V because excess voltage may destroy the IC. Now output from IC2 is given to loudspeaker with the help of transistor T2 and melody can be heard. After set time alarm stops and it will again sound when set time is over. If you want that it stop sounding alarm after preset time then connect a diode between pin 11 and 13 of IC1. Alarm will not sound until you again start the circuit manually.