A programmable timer is a device which can be used for switching a load ON and OFF after predetermined delays as per the requirements.
The delay timings are adjustable according to the users personal specs. The ON time delay and the OFF time delay are independently settable and this facility becomes the most important feature of a programmable timer circuit.
In this page we will discuss a very simple yet reasonably useful timer circuit diagram whose ON time and OFF time settings are independently adjustable through ordinary pots.
The idea becomes so easily configurable due to the versatile IC 4060 which require minimal number of component for getting the unit running.
Looking at the CIRCUIT DIAGRAM below we can see that two inexpensive IC 4060 have been wired up as two independent timer modes.
However though the timing settings are independent for the two sections, these are coupled with other such that their initialization become very much interconnected.
Basically both the configurations are similar and have been rigged in the standard counting modes of the IC 4060 devices.
How the Circuit Functions
The output of the upper IC is coupled to the reset input of the lower IC via a transistor in such a way that once the upper IC's output goes high, it triggers the lower timer into operation.
The lower IC then starts counting and when its output goes high, it halts the upper ICs counting and resets it to its original state and the process is initiated back from the start.
It simply means that as long as the upper ICs timing does not lapse the lower IC remains idle, however once the upper ICs timing lapses and its output becomes high, it switches the output load as well as the lower ICs operation.
The pot associated with the upper IC can be used for determining after how long the load will be switched ON, while the pot associated with the lower IC is used for determining how long the load remains in the switched ON position or simply after what time it should be switched OFF.