30 second timer

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

1. osmodia Thread Starter New Member

Aug 17, 2011
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0
Hi,
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.
Thanks

2. Kingsparks Member

May 17, 2011
118
5
Hi.
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.

Oct 15, 2009
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4. KMoffett AAC Fanatic!

Dec 19, 2007
2,574
230
Do you want normal clock accuracy? Are you going to power it from battery, or from a line-to-12VDC power supply?

ken

5. ErnieM AAC Fanatic!

Apr 24, 2011
7,386
1,605
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!"

"29..."

"28..."

It's very effective in clearing rooms fast.

6. AverageGuy New Member

Dec 27, 2009
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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.

Jim.

7. elec_mech Senior Member

Nov 12, 2008
1,513
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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:

http://home.btconnect.com/brettoliver1/masterclock.htm

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
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9. eblc1388 Senior Member

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

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10. DIG New Member

Sep 12, 2011
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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 Moderator

Oct 2, 2009
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3,360
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.