I have already discussed one programmable timer circuit in this blog earlier, the circuit involves the IC 4060 for generating the basic oscillations which is further used for generating the required time intervals, however this cannot be synchronized with an external clock.
The following circuit was requested by Mr.Amit, here the concept makes use of a clock for acquiring the required base timing oscillations and therefore is able to get synchronized with external clocks or watches.
The above procedure of using simple oscillator module for acquiring the oscillations may look quite impressive, but it accompanies a serious disadvantage.
Using an External Clock for Synchronizing Time
The above type of timers cannot be synchronized with a clock and therefore are never accurate.
The article explained here utilizes a clock's second's pulses for acquiring the basic triggering oscillations for the different sections of the corresponding circuit stages which are divided into minutes, hours etc.
These outputs are suitably configured with a set reset latch for obtaining the required programmable timer application needs.
As shown in the figure the circuit basically incorporates many 4017 ICs for dividing the source seconds pulses into minutes and hours.
How the Circuit Works
Each IC 4017 consists of 10 output ports which become high and low sequentially in response to the inputs applied at its pin #14.
It means if a pulse of one second duration or 1Hz is applied at the input, the Pulse will become of 10 seconds duration at pin #3 of the IC.
The first IC from left is applied with the seconds pulses derived from a regular digital clock.
As explained above, it's pin#3 now generates 10 seconds of time interval, meaning it goes high after every 10 seconds.
This pin#3 is next connected to the input of the second 4017 IC, which again does the same, increases the time interval *10, that is it generates 10*10 = 100 seconds time, however since its pin number 5 is connected with pin#15, this IC generates 60 seconds time duration at its pin#3.
This 60 sec time interval is further applied to the input of the next 4017 IC, which now in the same way transforms this input into a period of 60*10 = 10 minutes.
The above 10 min time interval is again applied to the input of the next 4017 IC producing an output of 10*6 = 60 minutes. that is equal to 1 hour at its pin #3.
The above procedure may be increased to any number of time interval outputs just by adding more and more 4017 ICs in the array.
Now interestingly, the timing generated at the respective IC's pin outs are all in accordance to the main input acquired from the digital clock's seconds pulse, therefore are perfectly co-ordinated with the clock timing.
If you are interested to achieve a programmable feature from the above set up, you just need to appropriately calculate, assess and integrate the relevant pin outs from the corresponding ICs to the SET Resest Latch circuit input trigger terminals, as explained below:
Using a Set/Reset Latch
The set reset latch circuit shown in the diagram is actually nothing but a simple latching set up, which can be used to activate a relay through one of the inputs (set) and reset it back to deactivate the relay via another input trigger.
The two input triggers are separate and may be individually acquired from the above explained IC 4017 pin outs. How you would like to achieve a particular set of triggering action as per your needs will solely depend how you analyze the above set up and configure the respective pin outs with the set reset latch.
The relay associated with the set reset latch will eventually be responsible for activating and deactivating a particular load discretely as per the assigned timing inputs from the 4017 ICs.