30 second timer

Discussion in 'General Electronics Chat' started by osmodia, Aug 18, 2011.

  1. osmodia

    Thread Starter New Member

    Aug 17, 2011
    I have an old station clock that works by receiving a approx 12 v pulse every 30 secs precisely; to move the minute hand. Does anyone know of a suitable circuit out there? There is a maplin one that could possibly do the job but I doubt its accuracy.
  2. Kingsparks


    May 17, 2011
    There are plenty of timer circuits that will do what you want. Try Google, "Timer Circuits" and take your pick.

    Once you find something you can ask about details and parts or functions you don't understand. With something to post and point to you will find all the help here you could want and it gives an idea of you knowledge level so we can respond accordingly. :)
  3. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
  4. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    Do you want normal clock accuracy? Are you going to power it from battery, or from a line-to-12VDC power supply?

  5. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    30 second timer, huh? Reminds me of the book "Starship Troopers" where the hero Juan Rico tosses in a "30 second bomb" to a room full of "skinnies." The bomb has a speaker and tape player and begins by announcing:

    "I'm a 30 second bomb!"

    "I'm a 30 second bomb!"



    It's very effective in clearing rooms fast.
  6. AverageGuy


    Dec 27, 2009
    This part, http://pdfserv.maxim-ic.com/en/ds/DS1306.pdf can be configured to generate a 1 hz pulse. Feed that into a counter circuit that counts to 30 and fires a relay/transistor to send the pulse to the clock.

  7. elec_mech

    Senior Member

    Nov 12, 2008
    Hi AverageGuy,

    Bill has a one-second clock circuit here:

    He explains how the circuit works which I found very helpful. You can then connect to a divide by 30 circuit (1/30 or 0.0333Hz = 30 seconds). How to do that you ask? Check this out:


    Go to about halfway down the page. The one-second clock generator is similar to Bill's. It is then connected to a divide-by-30 circuit using two CD4017's. I haven't tried this, but it looks promising.

    Hope this helps.
  8. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    Last edited: Aug 18, 2011
  9. eblc1388

    AAC Fanatic!

    Nov 28, 2008
    I would use a 32.768KHz xtal to clock a 8-pin PIC and have it generate a half second pulse every 30 seconds.

    Edit: add circuit diagram

    Last edited: Aug 19, 2011
  10. DIG

    New Member

    Sep 12, 2011
    I noticed your posting for a 30 second timer. I also have a slave station clock which requires a 30 second pulse at 1.5v (the coil is 6 ohms.) and I have been researching a solution. At first the solution appears easy, but the problems are many. Whatever timer is used it needs to keep running and in parallel needs to send a pulse every 30 seconds. The original master clocks were electro-mechanical, so it is not such a big problem. Electronic timers need to be reset and ones that have a repeat function usually wait for the quiescent timer to finish before the next timer cycle starts. That means there are timer delays. A lot of the timers use 555 chips which would not be accurate over a period of time. Precision timers are OK but there is a problem with the time taken to restart the next timing cycle (see http://www.quasarelectronics.com/ci0217-12vdc-precision-cyclic-timer-relay-module-0-60-seconds.htm). In the course of a week there are over 20,000 - 30 second clicks, so a few milliseconds variation will result in several minutes’ inaccuracy.

    One solution to consider is to use the movement from an inexpensive Kitchen / Office clock (see http://www.amazon.co.uk/Acctim-CK2602-Button-Wall-Clock/dp/tech-data/B00009KWEY/ref=de_a_smtd) which has a second hand. The second hand will initiate a pulse every 30 seconds, by either using a contact or photo cell. A clock with a second hand which has a counter weight on the other end of the hand is better. This will allow a light weight disc to be glued to the second hand with two holes in it for a photo electric cell to detect the timer pulse. In addition, it does not matter if the two trigger points on the 60 second sweep of the hand are not exactly aligned (e.g. 35 second pulse and 25 second pulse, as it will correct itself over a minute. Keep me posted if you find a better solution.
  11. MrChips


    Oct 2, 2009
    There are a number of possible solutions available.

    Forget 555 timers, they are not stable enough for real time clocks.

    For ultra stability and accuracy you could use a radio receiver picking up a time standard transmission or a PC with an internet clock receiver.

    Presuming that you want a simpler solution, a xtal controlled oscillator using a standard 32768HZ watch crystal like that suggested by L. Chung is a good possibility. However, all xtal clocks will drift with time.

    50Hz or 60Hz line frequency has better long term stability since the generation station will compensate to give the correct counts per day, as long as there is no power interruption.

    So my choice would be AC line frequency input to a simple 8-pin MCU, programmed to give you the required signal to drive your 12V solenoid.