24 hourTimer triggering a relay for 1 minute

Discussion in 'General Electronics Chat' started by aris, Mar 10, 2011.

  1. aris

    Thread Starter Member

    May 5, 2010
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    Hi all,

    I would like to build a timer that will count for about a day (24 hours) and then would trigger a relay for 1 minute. Thoughts that I make get me towards a PIC micro-controller (maybe series PIC10Fxx) but my programming skills are not the best.

    Could you suggest any other way of doing such a thing?

    Many thanks for your time!
     
  2. nerdegutta

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    Dec 15, 2009
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    What will happen in that minute?

    What will you be doing?

    What do you have so far?
     
  3. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    One possible solution but you'll need a I2C bus tool would be set the alarm on a DS1307 to trigger a 555 every 24hrs. You'd set the clock that way too, and external watch battery would keep time and alarms when the power is gone.
    Microchip makes a serial bus analyzer, my Junebug kit can be modded with that firmware to act as one too.
     
  4. aris

    Thread Starter Member

    May 5, 2010
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    I am sorry..to make this simpler I want to interrupt the power on a USB cable I want 24 hours to provide power to a USB dongle and then in for a minute to cut the power off on the dongle.
     
  5. Wendy

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    Mar 24, 2008
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  6. nerdegutta

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    Yet another way could be with the printerport of a Linux box, some printerport programing, a script and crontab.

    Then it would be like the old missile, The Maverick. Fire and forget.:D
     
  7. aris

    Thread Starter Member

    May 5, 2010
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    Could you please help me out with this one Bill. Thanks
     
  8. Wendy

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    Mar 24, 2008
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    OK, starting at the beginning. How accurate do you want it to be? An RC oscillator is much easier to build, but can be off as much as 10%, and will drift all over the place within that 10%. A crystal oscillator is much more accurate, but a lot harder to build. The crystal in the other thread is both cheap and common, and is usually used in digital watches.

    What part of the world are you? This helps with parts. If you are in the USA, for example, I may recommend parts from local vendors.
     
  9. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Simple...a 120VAC relay plugged into a cheap 24 hour digital wall-plug timer. These timers generally have a minimum on-time of one minute. ;)

    Ken
     
  10. aris

    Thread Starter Member

    May 5, 2010
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    I am in UK. I think that the "cheap" solution of the RC oscillator will be fine with me. I do not have a problem with the 10% drift.
    KMoffett this would be ideal but unfortunately I want this to work with 12V and not 110/240VAC
     
  11. Wendy

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    OK, it may take a day or two to draw it. If you look at the other thread you get a sense of what is involved. The good news is the other schematic is about 70% of the circuit, the two requirements are very similar.

    Feel free to jog me to this thread via PM, I won't discuss any details privately, but now and again I may need a bump to remind me to come back here.
     
  12. russ_hensel

    Well-Known Member

    Jan 11, 2009
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    Ideal problem for an Arduino solution.
     
  13. KMoffett

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  14. Wendy

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    Will the 12VDC be regulated? I don't think this is a big deal, but it would help overall. It will improve timing stability.

    By going with an RC oscillator the design is simplified considerably (and I do mean a lot). Right now I'm looking at 2 chips, a 555 and 4060. I suspect I have a lot easier time getting parts than you, so lets talk about what you can get or maybe have on hand.

    I'm looking for 2 tantalum capacitors, 10µF to 100µF 9VDC or better (higher voltage). This is the best option, and the larger capacitance values work best. A non polarized electrolytic cap, around 10µF to 100µF at 18VDC or better would also work. If you really don't care about long term stability we can use standard electrolytics, say 2 100µF 9VDC or better. It will work, the drift will be worse long term, but the capacitors are cheaper. I need to design around the capacitors you can get.

    What is your load? I suspect a relay is still needed, but depending on how you use the output maybe not.

    I will say the µC (microcontroller, either Arduino or PIC) is slightly cheaper, but not easier. What the guys advocating them aren't mentioning is the programing, which is a significant learning curve. If you are into programming they are the best option, the software replaces hardware (which is why they are cheaper). If you aren't into programming they can be a real nightmare. It is one of the things I plan on learning, I've bought an Arduino to learn on, but haven't got around to it yet. This issue comes up everything a project like this is brought up.
     
    Last edited: Mar 12, 2011
  15. Wendy

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    I was starting to draw the circuit (I will still draw it to your specs) but came across this in my notes. I've long ago lost track of all my schematics in my cookbook, this one is very close to what I'm going to do. A SSR is a Solid State Relay, which is pretty much what it sounds like. It will switch household line voltage very efficiently.

    [​IMG]

    This schematic is extremely close to what I was thinking about. When you push the button the 1 minute output is activated, and the 24 hour timer is reset. I do see a minor bug with it, but that will be fixed on the next revision.

    Calibration involves doing a real time measurement, using this to calculate what the circuit thinks the capacitors real value it, and calculating the resistor needed accordingly. I was planning on using a variable resistance, but it can be several none variable types instead. In either case you will need a DVM to measure ohms.
     
    Last edited: Mar 12, 2011
  16. KMoffett

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  17. blueroomelectronics

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    All the non crystal clock solutions will drift over time, calibration will also be difficult.
     
  18. Kermit2

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  19. Wendy

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    I've already done it with a crystal, and am in the middle of drawing the RC version. I don't think it will drift more than the 10% that was originally advertised with tantalum caps, assuming the original cal is close.

    All I'm waiting for is feedback from the OP for parts.
     
    Last edited: Mar 12, 2011
  20. KMoffett

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    Actually, it doesn't sound like the OP was concerned about accuracy, just periodically give a 1 minute power-off reset.

    Ken
     
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