This multipurpose adjustable timer circuit will give you alarm after every specific interval of time. You can vary the time interval with the help of 8 way dip switch. Therefore this timer can be used in kitchen, or by students preparing for competitive exam.
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 adjustable timer 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. You can set the time period for coking also like we used to in microwave oven.
3. Main advantage is this timer is it can be programmed for more than 250 different time interval.
4. It works off a 9V PP3 battery and its stand by current is also very low.
This simple circuit is based on CD4060 IC 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. Hear 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 delay for the period of 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).
With the help of this circuit we can form more than 250 combination. This is possible with the help of diodes D1- D8 which are forming AND gate. As we know AND gate will give us high output only when all inputs are high otherwise it will give you low output.
How AND gate is formed using diodes-
Diode is device which allow current to flow in one direction. Consider a case where anode terminal is at higher voltage in comparison to cathode than diode is said to in forward bias and its resistance is very low and it allow current to flow through it. Similarly when anode is at low potential than cathode, diode is in reverse bias and it does not conduct. In our circuit we are utilizing this phenomenon. As shown in figure below. If any one of the input may be A or B is grounded than current flow the diode and output will be low. And when both the input are high we will get the output. As we gate with AND gate.
Fig. 1: Circuit Diagram of AND Gates using Diodes
Working of this circuit is very simple. When power supply is given to circuit: IC1 stats its counter first you will output from pin 7 that is Q3 than pin pin5 that is Q4 and so on.
Now suppose we have on the switch connected to pin 14 and pin 6 through a diode and 8 way dip switch than we will receive an alarm after 4.8 seconds.
How to calculate the time duration-
We can calculate time duration for which output remain high with the help of below formula-
T = 2n/fosc in seconds
fosc = 1/2.5*(R2*C1)
Suppose we want to calculate the time period for Q7 output means for pin 6 then=
R1 = 10k
C1 = 1uF
fosc = 1/2.5*(10*103*1*10-6)
= 40 Hz,
therefore T = 2*32/40
= 1.6 seconds
Similar you can calculate time period for different pins. And set the time period according to your requirement.
Fig. 2: Prototype of CD4060 IC based Adjustable Electronic Timer