Garage Door indicator

Discussion in 'The Projects Forum' started by oxicottin, Jul 4, 2008.

  1. oxicottin

    Thread Starter Member

    Jul 4, 2008
    18
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    Hello, Im woundering if someone could help me with this? I want to build a garage door indicator so I know if the door is open or closed. Im new to building circuits so I dont really know alot so I need to know what materials to purchase. Anway I was thinking a red LED to show the door is open and on the door use a magnetic switch and when the switch touches when open then the light would light up. I would run this off an small 9 Volt battery possibly. But I would like to have a green status indicator if the door is closed but im not even sure how that could be done. Thanks!
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    Sure, something like that could be done.

    However, using a 9v transistor battery to drive an LED through a resistor (or other linear current limiter) wouldn't last very long; perhaps a couple of days.

    National Semiconductor used to make the LM3909 "Forever Flasher" IC, which would be ideal for your project. Powered by one "C" battery, it will flash a single red LED for a year straight.

    You can still find them occasionally. Right now, someone is selling them on Ebay for rather exhorbitant prices.

    But, there are other ways to skin the proverbial cat. ;)

    Rob Paisley has drawn up a schematic for a replacement LM3909 IC. It's reasonably well documented, and it should work OK. His LM3909 replacement page is here:
    http://home.cogeco.ca/~rpaisley4/LM3909.html

    So Rob's LM3909 redoux is practically your entire circuit, which you can power with a pair of "C" or "D" cells in series for long service - and because you're using a green LED, which requires more voltage than a red LED.

    For the switch on the garage door, I suggest something like this:
    http://www.itcelectronics.com/product_info.php?products_id=3819
    Magnetic Reed Switch, SPDT Open/Closed 0.5A @ 20V DC

    Screw the magnet to the door, and the switch to the door frame when the door is shut.

    Then run a 3 or 4-conductor wire (telephone wire would be perfect) from the switch to the box that has Rob's LM3909 circuit in it.
    The switch has three connections; N.O., N.C., and COM - or Normally Open, Normally Closed, and Common. Connect a wire to each, noting the color scheme.

    Back to Rob Paisley's schematic, you'll see on the upper left side there is a green LED. The cathode (pointy end) is connected to what would be pin 8 in a "real" LM3909, and the anode connected to pin 6.

    We're going to add a RED LED to the circuit. Connect the anode (longer lead) of the red LED to pin 6, along with the green LED.

    Now, the green LED's cathode needs to come off of pin 8. That's where you'll connect the COM wire from your door switch.

    The wire from the N.O. side of the switch gets connected to the cathode (short lead) of the green LED, and the wire from the N.C. side of the switch gets connected to the cathode of the red LED.

    That's it!

    When your garage door is closed, you'll have a flashing green LED; when open, a flashing red LED - just remember to change the batteries once a year. If the red LED flashes but the green doesn't, you'll know it's time.

    See the attached - it's a "pushpin" method of construction that someone sent to Rob. Works well for beginners. Basically, you make a printout of the schematic, glue it on a board, and put the real components on top, then solder them in place. He pulled the photo from his site, because I'm sure it caused a lot of E-mail asking about things, which I'll try to explain.

    In the schematic, where wires simply cross, there is no "dot" that indicates a junction. In the attached photo, some of the soldered junctions are clear, and some of the "hop over" crosses are hard to make out. Just trust me on this; in the attached photo if there was not a dot indicating a junction on the schematic, there is a wire bend OVER the other wire to avoid an electrical connection, also known as a short.

    I hope this isn't too much for you. If you feel that you're in over your head, but are interested in electronics, then ask questions.

    If you would like to learn a good bit of basic electronics, waltz on down to your local Radio Shack and pick up their "Electronics Learning Lab", that was designed and the lab books written by Forrest M. Mims III, a USAF Veteran and Citizen/Scientist held in high regard nationwide.
    http://www.radioshack.com/sm-electronics-learning-lab--pi-2102913.html
    The breadboard/experimenter's module itself is worth more than the price of the lab - but on top of that you get a number of components, jumpers for the board and most importantly Forrest Mims' fine lab books to guide you through many intriguing (and worthwhile) experiments.

    This is the best bargain that Radio Shack still offers.
     
    Last edited: Jul 5, 2008
  3. oxicottin

    Thread Starter Member

    Jul 4, 2008
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    0
    WoW :eek: SgtWookie, I really appreciate the thorough post..... I read it over and over but I am lost. Mabe im over my head or I just dont get it. Is the LM3909 basicly the whole thing? It seems to me if I purchase this LM3909 then thats all I have to do is connect a green led because the board is already done right? Thanks!
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    Well, the LM3909 is a timer and charge pump. It charges up a capacitor to a voltage high enough to light an LED briefly. You do need a couple of components external to the IC itself.

    The reason I steered you to Rob Paisley's page to begin with is that the LM3909 has been out of production for some time, and I don't know of a substitute - other than building one from discrete components (transistors, resistors, etc) - and if you bought one and it died a couple of years down the road, you'd have to find another one.

    Rob's adaptation of the datasheet schematic uses commonly available components that you should still be able to get 10 years from now.

    As far as building the circuit, getting an original LM3909 IC would eliminate most of the wiring and components.

    There's an E-bay auction going on now where you can pick up two of the IC's for around $6 + shipping. If you want to use the IC, you might pick a couple up there.
    [eta]
    I drew a schematic of how to hook up the "real" LM3909 IC in your circuit. See the attached. The only thing we haven't discussed so far is the capacitor. You'll need one somewhere between 0.3uF and 300uF. The datasheet says the capacitor voltage rating should be 3v, but standard practice is to use a capacitor with at least twice the voltage expected in the circuit for maximum life and minimal leakage current.

    A 300uF cap will flash the LED once per second. A 0.3uF capacitor will cause the LED to flash at around 1.1kHz. Basically, the larger the capacitor, the slower it will flash.
     
    Last edited: Jul 5, 2008
  5. m4yh3m

    Senior Member

    Apr 28, 2004
    186
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    Not to steer this off topic, but given the examples, it's somewhat relevant.

    SgtWookie:

    Is it cost effective or worth attempting to recreate discontinued ICs on a separate board using whatever components are needed to recreate the IC internals and modify your own "special project" to have a backplane to plug these emulated ICs in? I know it seems like a bunch of extra work... but if these ICs are being discontinued and (unlike the one mentioned) are difficult to access, would it not be beneficial to have the schematic to rebuild them and share with others who might need them?
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    Well, many devices are made obsolete due to similar functionality available in newer designs. The availability of very low-cost microcontrollers has decreased the demand for components that by their nature are limited in functionality. I don't know why this particular IC was discontinued; it had a very long production run.

    It may very well be that there is another IC out there which provides similar functionality to the LM3909, and I'm simply not aware of it.

    In the case of our OP (Original Poster), the LM3909 IC seemed to be a very good "fit" for their particular application. The "guts" of the LM3909 are relatively simple when compared to LSI/VLSI IC's, so it's not a huge chore to emulate the device using discrete components. The datasheet had the schematic of the actual IC in it, which isn't typical; usually you get a bunch of functional blocks connected together.

    I wouldn't attempt to do something like this for a production item; the relatively high parts count would make production costs skyrocket as reliability plummeted. But for a one-off project in a non-critical application, it could be worth doing.
     
    Last edited: Jul 5, 2008
  7. oxicottin

    Thread Starter Member

    Jul 4, 2008
    18
    0
    Well SgtWookie I have a electronics place called Hosfelt Eletronics close by and im sure they carry all these parts. I might not be on thier website but im sure they have it in thier store. I will show them the scamatic you drew and go from there.... Thanks!
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    Just checked their website.
    They don't indicate carrying the LM3909, or that they ever did.
    They indicate that they are OUT of 2N3904 and 2N3906 transistors.
    You could substitute 2N4401 for the 2N3904, and 2N4403 for the 2N3906. Fairly similar characteristics, but the 2N4401/2N4403 have higher gain and current handling capability than the 2N3904/2N3906 do.
     
  9. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    Both Cascade Surplus and Electronic Goldmine still have 3904 and 3906 transistors in stock. Neither has the charge pump chip listed on their website, but one could always ask via e-mail. I know for certain Cascade Surplus has items not listed on the website.
     
  10. SgtWookie

    Expert

    Jul 17, 2007
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  11. thingmaker3

    Retired Moderator

    May 16, 2005
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    I noticed Digikey also carries the 2n3904 and 2n3906. Looks like they might not be "obsolete" after all.
     
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