Advice on LED Stairwell Lighting

Discussion in 'The Projects Forum' started by >Chris<, Jun 3, 2010.

  1. >Chris<

    Thread Starter Member

    Oct 16, 2008
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    Hello everyone,
    now that I am on my summer break from school I thought I start a little project that keeps me interested in the school material :D
    What I would like to build:
    Ok so I would like to build a lighting system for my stairs. I was thinking about 1 LED on the side of each step, which should be sufficient to see where your walking when its dark. I would like to trigger the circuit with a sensor that recognizes that I'm going up or down the stairs. Lastly I would like the lights to turn on one after the other, with a little delay, in the direction I'm coming from.
    So if I walk down the stairs I would put the sensor on the top step and when I cross it I would see the lights turn on one after each other all the way down. When I go up then they should turn on from bottom to top.
    After that they should turn off the same way, either after a certain amount of time, or when the second sensor is passed.

    Alright this is what I had in mind. I haven't done any designs so far and wanted to check here what you guys think about the idea. I'm only one year into my electronics program at school so far and therefore still a bit limited but I thought this would be something I could be able to build over the summer.

    From the things I know rights now, I know the effect I would like to achieve with the lights turning on after each other can be accomplished with a shift register, but would it also be an efficient way? I mean I am aiming for about 12-15 steps and with a shift register I would need that many bits.
    Another thing is how to connect that circuit to the normal power in my house, because I obviously don't to run it on batteries :p
    I guess I would need to build a power supply and also a circuit to generate a clock.

    This is what I thought about so far. I would really appreciate if you could tell me if I'm on the right track or if I should design it completely different than that.

    Thank you,
    >Chris<
     
  2. retched

    AAC Fanatic!

    Dec 5, 2009
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    What if you ran half-way down the steps then remembered that you forgot you left the water running, so you turned around to go back up?
     
  3. >Chris<

    Thread Starter Member

    Oct 16, 2008
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    I was actually thinking about that to and for that problem I could use two sensors on the top and bottom (btw I was thinking about light sensors (I have no idea what they are actually called :p), so whenever you break the beam it triggers) and depending on which one breaks first the lights turn on or off in a specific direction.
    To go further I thought about what happens when more than one person go down the stairs, in which case I would need to implement a counter that would count how many people go on the stairs and then only turns the LEDs off when the last person gets off the stairs.

    Because I don't know how complex the main circuit actually is, especially at my level, I left it out and thought of doing it with just a timer for the beginning so it turns off after 15 sec or something.
     
  4. Markd77

    Senior Member

    Sep 7, 2009
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    You could have a sensor for each step, when activated it turns on the 3 steps in front AND behind. That way you get the effect and you can go whichever way and have as many people on the stairs as you want.
     
  5. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    If I had a stairway, I'd use a 12V wall-wart for power, a top & bottom sensor & illuminate all steps for 1 sec/step; avoids reaching for an illuminated step that's out of reach, or a change of mind & direction. Bringing a lead from each LED + common & control to common point involves a lot of wire. But maybe not near as much fun. Dont forget the day-night sensor.
     
    Last edited: Jun 3, 2010
  6. >Chris<

    Thread Starter Member

    Oct 16, 2008
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    Thats a good idea too but I would have to install sensors on every step and I don't know how much they cost. Can someone tell me what the actual name is for these sensors I'm looking for? :rolleyes:
    When I think about it though I would like to have the effect of all the steps turning on but if I would implement a sensor in every step that could also have a cool effect because then I could make every step turn of behind you and when you turn around to go back up they could turn back on.

    Are they common in electronic stores? I haven't thought about that. I'm definitely checking that out tomorrow.
    Edit: Ok I just checked on the internet they are pretty cheap. Why would I use 12V though? Don't most of the chips run on 5V?
    You mean they all turn on for 15 seconds or depending on how many steps there are? But then if I'm on the way down and decide to go back up then it wouldn't know that since there is only a sensor on the top and bottom.

    Thank for your input so far! I'm really getting into this which is pretty good since I'll be dealing with electronics my whole life now :)
    Do you guys know if shift registers are the way to go with this? Because I have the circuit set up on my breadboard and it's doing pretty much what I want, just that it's 4-bit and a way to complicated set-up :p
     
    Last edited: Jun 4, 2010
  7. someonesdad

    Senior Member

    Jul 7, 2009
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    I think you've picked an excellent project. It will also teach you a lot about designing things -- you'll find the design process interesting and it will force you to consider many things. This is excellent preparation for the tasks you'll face in the real world.

    Think about all the weird conditions and exceptions that can happen. For example, think about an old person going down the stairs. Will the lights turning on confuse them? If you use a timeout to shut the lights off, what if that old geezer is still on the stairs? What about a kid that wants to see how they can defeat the system? For example, they figure out how it gets turned on, then they go back the way they came, jumping over the beam or sensor that turned it on. (When I was in college, I read about college kids that were picking up the rear ends of their sports cars and carrying them over the rubber tube sensors in the road so that the counters would register half of a car. :p) You've got to show that you're cleverer than these kids. :) What happens when the power fails? How about when an LED fails -- do you want to detect that event? What if a dog gets curious and scratches at where the lights are mounted? Do you only turn the LEDs on when the ambient light level is below a certain value or do you do it all the time? Will the lights switching on or off in order affect an epileptic? Should the lights come on and stay on if a smoke detector goes off? How do you mount them so they avoid damage when vacuuming? etc., etc...
     
  8. retched

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    Dec 5, 2009
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    And, where will you attach, and how will you operate the oil slick function to keep would-be robbers and criminals from accending the stairs? The oil can spray onto the steps causing the criminal at the bottom of the stairs whilst you stand at the top taunting him/her.

    These are important things to think of! ;)
     
  9. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Some undigested thoughts: With a shift reg. you can insert another bit if a second person enters. With a 3 phase clock & 3 reg's can have 3 steps sucessively lit. With seperate up-down registers , the conflict of triggering both top & bottom , as if one person starts down, then another starts up. Now what happens when a person reaches the bottom- sensor is tripped stairs are illuminated going up. So now we need dual sensors- top & bottom to detect direction. Other IC options: 4017, 2 in series; binary counter up or up-down with 74C154 decoder[ 4 bit in 1 of 16 lines out ]. Power supply V depends on logic family selected & number of LED's in series. With only one LED/ step a 5V supply would do fine. If illuminating all steps at once for 20 sec., 'would use 12V with strings of 3 LEDs in series & 4000, 74C series ICs.
     
  10. retched

    AAC Fanatic!

    Dec 5, 2009
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    I would go with a sensor on each step lighting itself, the one ahead and behind it.

    so no matter which way you are going, or if you turn around, the next step is lit.

    Motion would activate them, so the old folks will continue to light the steps as they move.

    It will work simultainiously in both directions if one going up while the other going down. and a simple timer on each would give you the follow effect.
     
  11. Bernard

    AAC Fanatic!

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    Individual sensor per step might not be to expensive. Just for example: IR emitter G14583 2mW @ 20mA 1.6-2V, 20 deg. = 3/ $1.
    IR module G14384 36kHz = 5/ $1.
    Bright Wh LED G16402 10,000 mcd, 3.2-3.4V @ 20mA, $ .49
    Missing pulse detector, 555 + sm parts =+- $1
    Pt #s The Electronic Goldmine.
     
  12. retched

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    There you go. $20 and a hand full of 555s and you got yourself a person-sensing-stair-lighting device. ;)
     
  13. >Chris<

    Thread Starter Member

    Oct 16, 2008
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    Thanks for all your suggestions!
    Later I'll go to the apparently cheapest place in Montreal to buy electronic parts ans see how much some of the parts are. (Or not since they are closed on Saturdays :p Well I'll go another place then :D)
    I have one more questions though :rolleyes:
    How do you make the LEDs *fade*? So if I would use the method that always 3 turn on at the same time they can turn on instantly but how would they slowly turn off and dim until they are off?
     
  14. retched

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    When you get some 555 chips, you can read about PWM/ Pulse Width Modulation

    that will allow you to adjust the brightness of the LEDs.
     
  15. Bernard

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    Here is one way to have dimming & feed forward, L-leading, T- trailing. BB = beam break, O = out. Each step has one module, each powered with 9V DC. The BB is from a 555 configured as a simple beam break [ top & bottom stair ] or missing pulse detector when using modulated IR emitter. When BB goes high, C1 charges rapidly, discharges slowley after BB goes low, LED about half bright in 2 sec. Second stair comes on at slightly reduced output, 3rd on dim, 4th off. Breadboard used 2 ea 2N3904's in darlington configuration, MPSA13is a darlington. R3 controls LED current @ about 20mA. Module output,O, drops about 2V for each cascaded stage, 2nd 6.6V, 3rd 4.6V, 4th to low to activate. C1- R2 control decay time. Other values OK, R = or lower than 1M. R4 only for short ckt protection.
     
    Last edited: Jun 6, 2010
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  16. retched

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    That could work.
     
  17. >Chris<

    Thread Starter Member

    Oct 16, 2008
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    Ok I don't really understand how the Transistors work yet but I'll build this on my breadboard and see how it works :D
     
  18. Bernard

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    The reason of using a compound transistor, darlington, is to present a high impedance to the RC timing , so that R2 predominates in discharge time. Estimate input Z= about 2.5meg ohms, B X B X emitter resistance of around 333 ohms. MPSA13 shows DC current gain of 10,000 @ 10mA. I think the discharge time with R2 out, was around 5 sec. using 2 2N3904's.
     
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  19. >Chris<

    Thread Starter Member

    Oct 16, 2008
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    Hey everyone!
    Sooo, I finally got to work on this again! Due to some major financial problems and other stuff I just didn't have time to work on this project, but now I'm getting back to it.

    Ok so I built the suggested Circuit Bernard posted on my Breadboard and it works fine.
    The only thing is the problem with the shutdown point of the LEDs. I did some research on the Internet and found out that pretty much every LED has a different point where it actually turns of completely. I read that it's not recommended to have a setup like this with a Capacitor and rather get the dimming effect with PWM.
    Can this circuit be modified in any way to get around the problem or would I need a completely different design and incorporate PWM?

    Thanks for all your help!
    Christopher
     
  20. thatoneguy

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    Feb 19, 2009
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