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.
Using Versatile IC 4060
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.
The LED positions have been changed in the following updated designs, because the earlier LED positions were conflicting with the relay operations, and therefore the positions have been relocated for ensuring foolproof operations.
Circuit Diagram of a Versatile Programmable Timer
Video showing the proposed 2-stage programmable timer circuit with LEDs
Using a Start Push-Button
The above design could be upgraded with a push-button to facilitate a push button start. This further ensures that the timer shuts off completely in case a power failure occurs while the circuit is operational, which in turn ensures that crucial loads like heater, or geyser are completely turned OFF during such situations.
Calculating RC Timing Components
It can be done through a formula, but the manual way is much simpler and accurate. It can be done as explained below:
- Connect any arbitrarily selected resistor above 100K in place of P2/R2 in the upper circuit.
- Switch ON and carefully note down after how much time pin#3 of upper IC 4060 becomes HIGH. This will be your "sample delay".
- Once this is noted, other desired time delays could be calculated using the following simple cross multiplication:
Sample Delay / Desired Delay = Selected Resistor / Unknown Resistor
Customizing the Above Concept
This circuit of a flexible programmable timer circuit explained in this article was designed by me in response to a request by Mr.Amit. Let's know more about the request and the circuit details.
"I need a circuit for my auquarium where it should do the following
it should switch off the lights at 10:00 pm and start at 7:00 am daily + switch off the light at 12:00 pm daily and switch up at 6:00 pm back.
this will help to make my fishes live longer. 🙂
Thanks in advance.
So here's the circuit that I came up with. As the name suggest, the timer is pretty flexible and may be adjusted to produce any desired time periods, according to the above requested format.
The circuit consists of four identical stages, made up of the IC 4060 timer configuration. Te timer sequence begins from the IC at the top left corner.
When power is switched ON this IC starts counting. Depending upon the setting of its pot, the IC triggers after a certain period og time interval.
This switches ON the relay and the driver transistor BC547 which consequently switches OFF the connected lamp. The stage gets latched with the help of the diode connected across its pin 3 and pin 11.
The above triggering also switches another BC547 transistor which connects the reset pin of the next IC 4060 to ground which initiates this stage also.
After a predetermined time, this IC also triggers its output at pin3 and gets latched by the corresponding diode, however this actionsends a feedback signal to the relay driver transistor, instantly switching it off and restoring power back to the lamp so that it lights up again.
Just as the above actions, the sequence further proceeds and switches ON the third IC 4060 in the line which counts the set time interval and pulls the relay back to OFF position via the diode connected to the collector of its bc547 transistor, such that the lamp again gets switched OFF.
As soon as the above triggering happens the last section at the bottom right corner switches into action and counts as per the setting of the respective pot, until the ICs output becomes high, this high reset the the first IC and switches ON the lamp once again so that the process may be restart the cycle all over again.
The pots may be increased to 3m3 for generating higher time interval periods, so is true with the respective capacitors.
How to Adjust and Set Up
The timer may be adjusted as per the sent request, in the following manner:
If we consider the first timing sequence to begin at 7am and end at 12pm, means the upper left timer's P1 needs to be adjusted such that it activates the relay and switches off the relay after exactly 5 hours.
For keeping the lamp switched OFF in the above position and switch it ON back at 6 pm we now adjust P1 of the upper right timer section such that its output triggers after another 5 hours. This switches ON the lamp again.
The above situation needs to be kept intact until night 10pm, which is about 4 hours of period, therefore we adjust the lower right timer's P1 to get it triggered after 4 hours of time interval.
Finally, for initiating the above procedure back again the next morning at 7am, P1 of the last timer at the lower right is adjusted such that it resets the first timer after 9 hours..... and the cycle repeats.
For making the circuit work according to the above specified timing pattern, after adjusting the respective hours, the unit should be powered or switched ON exactly at 7 clock in the morning....rest will automatically follow.