DIY help needed for pulse circuit

Discussion in 'The Projects Forum' started by prdaniels, Aug 8, 2010.

  1. prdaniels

    Thread Starter New Member

    Aug 8, 2010
    11
    0
    Hi there,

    Two quick disclaimers:
    1. I am a newbie, so if I look lost with this post, please direct me to where someone might be able to help me (and apologies)
    2. I am a DIYer with some practical know-how, though admittedly I'm enquiring about an off-the-shelf solution to my problem (ideally)

    Cool, so the problem I'm seeking help with is that I want to create a small fan which operates intermittently. The fan should ideally run for a few seconds every hour or so. The timing is not critical, but should be around this: if it ran for a few seconds every few hours, that would be ok too. It only needs to control a tiny fan, an inch or two diameter. And if it could run off 9V or lower, with the ability to run for a good while (i.e. months) then that would be great.

    The application of this bizare set of criteria is that I want to fit a compact fan into my cigar humidor (within a custom build cedar box). It would help regulate the humidity evenly around all the cigars so that there are not microclimates of high and low humidity. Cigars should ideally be kept around 65-70%RH, but I have noticed through scrupulous measurements that the humidity pools at the bottom of the humidor, leaving the top somewhat drier and the bottom noticably wetter (running the risk of mould forming). The humidor is only about 500 cubic inches in volume, hence the need for only a small fan to disturb the air inside and for only a brief period of time.

    So, in short, I'm wondering if anyone can help by suggesting an off-the-shelf circuit which I could programme/adjust to the timings about (on for a few seconds every hour), which I could put between a fan and a battery. I'd be confident about following a kit, soldering, and so on, but maybe not so much building anything from scratch.

    Left-field solutions also welcome. I.e. solutions which are perhaps not premised on a circuit inbetween a battery and a fan.

    The help would be SOOOO much appreciated, I just don't know anyone who specialises in this sort of thing. If you are in Melbourne, Australia, I will buy you a beer.

    Cheers,

    Paul.

    P.S. I should also add that I have trawled the net for many hours trying to figure out what it is I need, but I have been a bit bamboozled by some of the terminology and technicalities. I'm not just trying here as a first resort for an easy fix, this is my last resort!
     
    Last edited: Aug 8, 2010
  2. nerdegutta

    Moderator

    Dec 15, 2009
    2,515
    785
  3. windoze killa

    AAC Fanatic!

    Feb 23, 2006
    605
    24
  4. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
    201
  5. prdaniels

    Thread Starter New Member

    Aug 8, 2010
    11
    0
    Thanks for the help so far guys, but so far I haven't found the silver bullet I've been searching for.

    Nerdegutter, cheers, I'm pretty au fait with the techniques of humidification in a small home humidor, but like all closed systems with humidification devices inside, the humidity tends to pool at the bottom of the humidor about 4% more than at the top. The humidifiers I use - like most humidifiers - release or suck up moisture to keep the ambient RH% at a set value (in my case, 70%). This sounds great, and is the best solution on the market for storing cigars, but it still suffers from the above problem. I'm looking to improve on it with this little fan which can disturb the air (i.e. those bubbles of higher humidity) for just a few seconds every hour or so.

    Similarly, thanks marshallf3 for pointing out the RH% as this would prove a useful switch indeed, but for the reasons above it would only be effective if placed in exactly the right spot in the humidor... but hey maybe that's not a bad idea.

    Windoze killa, lastly, if your circuit does what it says it will do: fantastic, a guinness is indeed coming your way. It is a little too technichal for my skills, though. An off-shelf-solution may not be around, and if I've got to go for a circuit like this, I'll need some help!

    The closest I could find online which seems to fit the description are circuits like these - though they all seem to fall short in some way...

    http://www.apogeekits.com/timing_kits_modules.htm

    http://www.apogeekits.com/relay_switch_k8015.htm

    The CLOSEST overall seems to be this bad boy:

    http://www.apogeekits.com/interval_timer_555.htm

    But its 'pulse' and 'pause' times are just too small, i'd need them to be larger (or at least the pause time).
     
  6. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
    201
    Keep looking at some of the 1,000s of websites containing 555 & 556 circuits as well as some of the data sheet app notes from TI and the others. Your answer is there.
     
  7. prdaniels

    Thread Starter New Member

    Aug 8, 2010
    11
    0
    Hi guys, following marshallf3's advice I scanned the net for more solutions. The following site seems promising:

    http://www.reuk.co.uk/buy-REUK-SUPER-TIMER.htm

    It seems to fit the bill, but can anyone then inform me if it might be able to run a tiny fan, i.e. if it is likely that the voltages will be compatible, that the battery will last more than a few months, etc., etc. I've seen you can buy quite compact 12VDC batteries, such as:

    http://www1.duracell.com/oem/Pdf/MN21.pdf

    I'm guessing a couple of these batteries would keep this system going for a good while?

    Is there a way to calculate roughly how long it would indeed last?

    Cheers
     
  8. whale

    Active Member

    Dec 21, 2008
    111
    0
    Instead of buying kits, you can make your own one. you can use 555 timer IC to time the activation period of your fan. since you said that its enough if the fan gets on for some seconds in a hour, lets take it 60 seconds. then you will need a pulse with pulse duration of 3600 seconds. The frequency will be 0.00027778 HZ. The timing signal at the output pin of your IC can be connected to amplifier circuit to drive your fan.
     
  9. prdaniels

    Thread Starter New Member

    Aug 8, 2010
    11
    0
    Thanks guys, I have kept looking around for kits and so on - Sorry, whale, I just don't have the expertise to design and execute a circuit on my own.

    Based on the project I want to complete, what about some of the attached kits? Do they sound like they might do the trick?

    The offer of a beer is still there...
     
  10. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
    201
    The circuit is too easy to make to be shelling out money for a kit and although small fans are usually somewhat inefficient you should get plenty of life out of one of those 12V photo batteries as most are lithium.

    If you source them from the Chinese sellers on eBay you can often pick them up for a decent price with free shipping if you buy them in quantities of 10. I don't know how they do it, but when I found that you can buy most any of the coin cells at 99 cents for 10 with free shipping I got one of those multi-drawer parts bins and stocked it with everything but two of the oddball lithium ones that nobody sells for cheap. I now have a drawer bin that holds all the coin cells as well as AA, C, D, 9V and a misc drawer so I'm never having to pay $3 a cell at Radio Shack anymore for the multitude of tiny gadgets I have around.

    I guess in time I need to post my completed label set templates for my parts bins, here's the one for the batteries:
    http://www.innoengr.com/images/drawer_labels/battery_labels.doc

    It's designed for Avery 5195 labels and uses a 39 drawer Stack-On bin from Amazon, about 19.99

    [EDIT:] I also made up a nice pair of cross reference sheets that I printed and put back to back in a sheet protector then stapled them in there. I just keep it by the box. Can't find the files here at home but I've got them at work when I get there. I can't FTP from work so I'll send them back home and put them on my website later tonight. If you follow my example you'll have a nice simple addition for your work area that also comes in handy when a neighbor's car remote quits working or you've got a watch that needs a battery. You can even get the special tool with a multitude of different tips for screw-off back watches from eBay for $6.
     
    Last edited: Aug 9, 2010
  11. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,170
    395
    Look at old post by JPK777, on humidor fan controller.
     
  12. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,170
    395
    How long wuill motor run: At 80mA, 5 sec/hr on a AA, 2700mA battery- about 2.5 years- unless I goofed somewhere. Using two AA's, one for motor, second to give 3V for C555; switch batteries after 2years and it runs over 4 years on a set. 100μF & 1MΩ timing, 47kΩ, discharge, pin6 to 7, pin 3 to 27Ω to base of high gain PNP switch, and maybe 5 years. First need motor specs.
     
  13. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
    201
    In addition to my post about making up a coin cell collection and labels for it I promisd I'd post the cross reference I keep by the box.

    39 drawer Stack-On box ($20 at Amazon or most hardware stores)

    Labels (print 0n Avery #5195)
    http://www.innoengr.com/images/drawer_labels/battery_labels.doc

    Cross Reference: (print, insert back to back in sheet protector and staple in there)
    http://www.innoengr.com/images/drawer_labels/coin_cells.xls
    http://www.innoengr.com/images/drawer_labels/lithium_coin_cells.xls
     
  14. prdaniels

    Thread Starter New Member

    Aug 8, 2010
    11
    0
    Thanks for all your help guys.

    Looking around further, it appears as if cigar people simply use an Oust fan without the perfume. The fan turns on for five minutes and off for 15 minutes, which is close enough for me and reportedly does the job really well.

    I really am grateful for the suggestions, but at the end of the day I have to evaluate my own ability to construct a circuit, and since there appears to be little in the way of off-the-shelf kits that will do the job, I'm bowing out in favour of the Oust fan.

    Also the Oust fan doesn't gobble up the same sort of power when it's in quiet mode, when the circuits suggested all seem to eat a noticable rather than negligable amount.

    Once again guys, many thanks.

    prdaniels out.
     
Loading...