Timer Circuit with Auto Pause and Resume During Power Failures

The post explains an innovative solution which could be used for pausing the counting process of a timer IC during power failures, and also restart the process when mains is restored, ensuring an uninterrupted functioning of the timer. The idea was requested by Mr. Arun Dev.

The Circuit Request

hello sir... this time i am gonna discuss about a different subject.... The intention behind making of this one is given below :

I need a timer circuit which should activate a relay for the determined time interval and thereafter deactivate it until a manual operation is detected...

The main purpose of doing this circuit is to charge my laptop or mobile phone over night keeping it charging for a few hours ( say max. of 4 hrs ) only......

thereafter charging cut off immediately.... even though the main intention is for charging, i also want to integrate this to operate a particular electrical equipment as per user's time decisions....

This can easily be carried out using a relay to switch the AC voltage as seen in the attached figure.....

but the only one problem regarding this is that :

whenever a power failure occurs during its ( timer ) working period, the CD4060 IC automatically gets reset and the timer starts from beginning when power returns.....

SO ANY IDEA TO PAUSE THE WORKING ( COUNTING ) OF THIS IC DURING POWER FAILURE AND RESUME FROM THAT POINT WHEN POWER RETURNS TO MAKE SURE THAT THE CONNECTED EQUIPMENTS ARE WORKING ONLY IN THE USER DEFINED TIME ??

Circuit Schematic

The Circuit Design

The modified version of the above 4060 timer circuit can be witnessed in the following schematic. The circuit includes an automatic pause and restart feature of the IC's counting process during power failures and restorations respectively.

 

The sections which are colored in blue are the inserted modifications, we can see a battery backup being added at pin16 of the IC via diodes, and a relay at pin9 of the IC.

Since the capacitor C3 is responsible for initiating the counting process of the timer while it gets fully charged, this component could be targeted for the intended pausing/resuming of the timer.

As may be seen in the diagram, this is simply implemented by connecting C3 to the "hot" pin9 of the IC via a pair of relay contacts (N/O to be precise).

However for making the above implementation work, the ICΒ  needs to be supplied with its fundamental operating current and voltage while the mains is not available.

This is done by adding a battery back up to the IC via isolating diodes at pin16 of the IC.

The associated 10K resistor makes sure that the battery keeps getting the required trickle charge as long as the mains continues to be present.

When power is first switched ON, the relay at pin9 activates and connects C3 in the line so that the IC is able to initiate normally and begin its counting process.

During Mains Failure

In an event of a mains failure,the battery takes over and keeps the IC powered in an uninterruptible manner, while also simultaneously the relay at pin9 of the IC disconnects C3 from the line in order to stop the capacitor from losing the stored instantaneous charge via pin9, this ensures that the elapsed time period gets locked inside the capacitor for that particular moment until the mains is restored.

The moment mains power returns C3 is connected back with the circuit by the relay, enabling it to resume the counting process exactly from where it had stopped and not from zero as it would otherwise do if the above mods weren't included.

The above could be also identically implemented in other timer ICs such as in IC 555 monostable circuit or IC 4047, IC 556 IC 4022 etc.

As discussed in the comments the above designs may have some limitations and flaws, a reasonable approach may be witnessed in the below given diagram which would hopefully allow minimum discrepancy, not more than 1% +/-. See the relay connection in blue across R4 and the inclusion of the high value 10M hold resistor.

 

 

32 thoughts on “Timer Circuit with Auto Pause and Resume During Power Failures

  1. Have questions? Please feel free to post them through comments! Comments will be moderated and solved ASAP.
  2. Thank you very much sir…. But i got the required functioning by giving positive signal to diode D1 during power failure.
    But really i don't need such rechargeable type batteries to be used to power up the whole circuitry under power failure…. The only thing i need is a normal replacable 9 V to be used for that purpose… therefore the charging is not necessary.. So can you help me in identifying how to use such a battery in this circuit….. can i use a single diode for that purpose ?? will the config. in which the battery dpositive connected to the above circuit using a diode , block the dc voltage from the battery in flowing towards the IC during mains is present ???
    also suggest a suitable solution to give a possitive signal into the diode D1 during power failure…. i have used a simple logic for that by referring one of your LED emergency light circuit ( given in the following link )…..On doing such modifications , the IC stopped from oscillating further and became paused …but the real problem came after that …… when mains returned, the IC continued in its freezed state…..

    http://4.bp.blogspot.com/-TE9jiuDHtyM/TuWsC3jIL5I/AAAAAAAAAMg/84UEd0gQ2hg/s1600/Emergency Light Circuit Using 6 Volt Battery%252C Image.jpg

    i have used the logic in this config. to switch the Diode D1with a positive signal during power failure

    • Arun, if you have employed the PNP triggering method as shown in the above link, then the diode positive should have got inhibited allowing the IC to resume its clocks?

      Please confirm whether the positive from the battery is getting blocked or not by the PNP as soon as mains returns.

      You can use the ordinary 9V battery also in the same position as shown in the diagram, simply remove the 10K resistor since it won't be required now.

      If possible I'll try to update the above article soon

    • the positive to the emitter of the PNP should be derived from the battery positive directly and the collector to pin11 of the IC via a diode, 1N4148 preferably.

  3. Sir, i have tried everything as you suggested…but still the OSCILLATION in IC is getting freezed in its paused state even after power supply returns…. Disconnecting the capacitor lead from pin#9 of IC as in this article also didn't give the intented results…. the IC was also in the freezed state in this case….

    One thing i have noted is that, Oscillation in CD4060 is getting resumed iff the duration of power failure is very short ( say 1 mnt )…. in all other cases the IC can't resume its Oscillations…

    • Arun, can't say much until I check it myself….in the meantime you can try the same with a 555 IC by disconnecting the capacitor from it. If it works, it's timing could be easily amplified with a 4040 IC for getting any delay duration

  4. Sir this config. will never work….. i have tested it practically….. because, whenever the contact between the Capacitor terminal and PIN#9 of IC cuts during power failure ( keeping the ic working under auxiliary battery power ) the Voltage at pin#11 of IC becomes high automatically thereby counting ceases….but the problem is ,that pin remains at high state even after power returns keeping the oscillations ceased eventhough the capacitor contact is getting joined with pin#9 again……so it requires a reset for a new counting to begine

    • Arun you can try replacing pin10 of the IC instead of pin9 with the relay contacts and see the response from the IC….because as per the internal schematic of the IC this modification could result in locking of the oscillation and also stop the capacitor from discharging further.

  5. Happy independence day sir…..
    hope u have read my last email… another thing to inform you is that ; i have also tested this circuit by giving a possitive signal to the diode D1 during power failure….. it worked….but sometimes that given signal is being latched in the diode side even after power returns similar to the problem discussed in my email…..also whenever it is functioning, the remaining time duration just after the paused state not attains the target time

    • I haven't checked your email yet, will do it soon…

      we'll have to figure out some out the way solution for solving this….may be add another circuit that would add the mains off time with the 4060 set time for compensating the lost period…something of that sort.

  6. The idea z nice sir ….. but why it z necessary to know the mains off time ???
    This circuit is set for predetermined time duration ( say 5 hrs set by 2M2 in place of the pot )….. let us assume that main fails after 3 hrs……. the power cut is assumed to be 4 hrs….. then if we are placing the entire circuit for operating for 5 hrs initially without knowing about any such power failure which z gonna occur in the nearby future, then the following will occur :

    CASE 1 : timer stops operating after 3 hrs ( when power goes ) and will be idle for 4 hrs during power failure
    CASE 2 : Timer continues operating during power failure and will get turned off after 2 hrs…

    in both cases whatever it be why it is necessary to know the mains off time ?

    • yes the mains off time cannot be used, won't serve any purpose here, i just thought quickly and tried to provide an example of the type of remedy that may be suitable, it wasn't a final thought or design from me.

      I will require some thinking….

  7. Hi !
    I don't know how to ask this , but i guess from the following words you'll understand what I mean.

    " I want to make system ( amplifier) which will have delay power on for 5sec(adjustable). During that delay period, another circuit will be working led chaser. The amplifier will be powered by a push button switch (whatever N/O or N/C) "

    Working : consider the following;
    A as push button (on/off with LED green/red)
    B act as a loading effect (LED chaser ,,10-12 LED)
    C power amplifier (wait 5sec after A pushed)
    Once plugged in, the system will be at standby mode ( with red LED on), when the power button is pressed , B will start working for 5sec only (adjustable) after Delay period , C will start to work. B should remain off until the system is restarted.
    those circuits can be operated by 6-12dcv, preferred single supply if possible

  8. Hello Swag,

    Your articles articles are good and it is very helpful for beginners to learn about the circuits. Thank you for these articles.
    I have one request for you. Can you design the same circuit to continue counting without pausing during power failure with the help of battery backup. Is it possible to use 8V lead acid battery(two 4v battery connected in series) to power the circuit during power failure.

    Thanks and Regards,
    Raja

    • Hello Raja, thanks very much!

      if you are using a battery as a back up source, then it becomes absolutely easy to maintain the counting process without any kind of interruption even during power failure.

      No modifications would be required in the circuit except the pin#16 connections, which will need to be wired with the battery exactly as indicated in the diagrams.

    • Thank you for your quick reply swag.

      I want to know the current consumption by this circuit, so that I can decide the respective battery backup. In previous comments you have mentioned that 9V batttery is sufficient to power this circuit. I am planning to use 8V 1.5 Ah lead acid battery(two 4v battery connected in series) with float charging. Is it ok to use 8v battery for powering the circuit alone.??

      Thanks and Regards,
      Raja

    • Raja, if the relay is not allowed to operate then your battery could last for days, since the current consumption of the circuit without the relay is not more than 5mA

      the relay could be stopped from activating during the battery back up by connecting the battery positive with the circuit through a resistor….a 10K will do.

      8V will be more than sufficient



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