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Motion sensor timing

Discussion in 'Sensors and Actuators' started by Katie Davidson Smith, Feb 9, 2018.

  1. Katie Davidson Smith

    Katie Davidson Smith

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    Feb 9, 2018
    I'm a university product design student who doesn't have much of an idea about electrics but I need help for my project. I'm creating night light that needs to be turned on from a piece of paper sliding through a slot.
    I've been looking at motion sensors that turn turn on lights but I cannot find any that keep a light on longer than about 12 minutes. I need something that would last for lets say two or three hours.
    Can any one help?
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Look into photoelectric through beam sensors. Here's an example. You'll need additional electronics to evaluate the sensor signal and control an actuator.
    Off the shelf modules are available e.g. for the Arduino platform.
     
  3. hevans1944

    hevans1944 Hop - AC8NS

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    So why would you choose a project requiring "electrics" of which you don't know much about?

    Why? How is this "better" than using an ordinary manually-operated toggle or rotary or push-button switch? Have you seen a device marketed as "The Clapper" which turns a light on or off at the clap of your hands?

    What is the purpose of the paper? What size and thickness is it? Will it buckle if it encounters resistance when you attempt to slide it through a slot? How much light will pass through the paper if a photoelectric sensor is used to sense the presence of the paper? Perhaps the paper's dielectric properties vis a vis air can be used to distinguish its presence or absence? How is the paper slid through a slot? Is it stiff, like card stock? Is there a motor-driven roller that pulls the paper into the slot when the presence of the paper is somehow sensed? This is a common mechanism used to detect larger denominations of counterfeit currency and may be apropos to your product design, although it sounds a bit like overkill just to turn on a night light.

    It is easy to purchase a PIR (passive infra-red) motion detector module, attach it to an Arduino, create and download a program into the Arduino that will detect motion and turn on a light for whatever interval you desire. There are folks here that can help you with that.

    Please tell us what you are trying to DO, rather than presenting proposals (PIR motion sensor, paper-in-a-slot) of how you think it should be done. Many so-called "products" are really just someone's idea of a solution looking for a problem to solve. Please convince us your product doesn't fall into that category.
     
  4. Katie Davidson Smith

    Katie Davidson Smith

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    Feb 9, 2018
    Thanks for the reply pal, I don't know if the tone of your message was supposed to be quite so condescending but unfortunately the way that my project has turned I cannot avoid electronics but I would of thought that any body from the 'electronics world' would be excited at the prospect of more people wanting to educate themselves.

    My night light is a way for children suffering from bad housing to feel more at home. The piece of paper passing through through the gap would be an ordinary folded piece of paper through a money box like gap. The task of turning the light on from this action is a way of motivating them to use the piece of paper.

    Thank you for your alternative advice though, I will make sure to look into the Arduino programme you suggest! That seems like it could be quite fun.

    Thank you again, the advice is appreciated!
     
  5. Hopup

    Hopup

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    Jul 5, 2015
    Photoelectric sensor is probably good idea as Harald said already.
     
  6. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    Not condescending at all. Here at Electronics Point we get a LOT of "drive by" posters looking for a quick answer to their problem. That isn't what EP is about. This is a discussion forum for folks with a genuine interest in electronics, whether a rank beginner who knows almost nothing about the subject (that would be you) or an uber-expert who has been around the block so many times they have lost count (that would be me and a bunch more that you will meet if you stick around). And of course there is everything in between. All are welcome to participate here.

    The key to participation is a meaningful dialog, a back-and-forth exchange of ideas.

    Meh. People get excited for many different reasons, most of them irrational. I would like to "be excited at the prospect of more people wanting to educate themselves" but that's very much a personal decision on their part.

    I will encourage someone who shows an interest, perhaps even by mentoring them. Amateur radio operators (Hams) who help other Hams are called Elmers. I try to be an Elmer to people here from time-to-time, if I sense they are willing to put forth some effort on their part. However, this is NOT an educational forum. Students are responsible for, and are expected to do, their own homework outside of formal school hours, on their own, in a self-paced environment. Folks who are capable of making that leap of faith... learning just for the sake and sheer joy of learning... often become hobbyists. Many of us here started that way, and many may have added formal education years later. Or not. You can become educated along many paths. Participating in this forum may be one of them.

    This comment is useful to the discussion:
    Well, okay. But what is the point of "motivating them to use the piece of paper?" How does that make children suffering from bad housing feel more at home? I can see how a night light might be comforting to a small child, but if they already live in bad housing is a night light even going to be affordable and available? Will electricity in bad housing be reliably available?

    The optical interrupter that @Harald Kapp linked to could easily serve as the paper sensor. Some assembly required to "guide" the folded paper through the slot and past the sensor. Some logic required to ensure the paper is fully inserted in the slot and is later retained by the "money box". Perhaps gravity can be your friend if the slot is oriented horizontally, on a level surface and the folded paper drops down through the slot on its way past the optical interrupter. An Arduino Uno appears to be an ideal complement for use with the optical interrupter. You will also need a solid-state-relay (SSR) controlled by the Arduino, to turn the night light on and off.

    The Arduino requires connection to a personal computer, such as a laptop or desktop PC with a USB port. You then download the Arduino programming environment (free) from the Internet, connect the Arduino Uno to the USB port and write your stand-alone program, called a sketch in Arduino-speak, using the PC as your program development platform. The program is written in a version of C++ and is compiled on the PC and the executable is then downloaded to the Arduino as a stand-alone program. Once you have it working, the Arduino USB connection can be removed and the Arduino operates as a stand-alone processor, sensing the paper and responding by turning on the night light for whatever interval you have programmed. That's the essence of it. You can add "bells and whistles" later as you become familiar with the Arduino Uno.

    Arduinos are lots of fun to work with. Sketches can be trivial and simple or complex and difficult to debug. There are lots of user groups and forums dedicated to all things Arduino. Check them out and then dive right in. Using off-the-shelf components, you should be able to finish your project in a week or two at a cost less than fifty bux.
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Katie, it's just frustration.

    The problem we have is that people with no knowledge come to us with the solution they have thought of, wanting help with it. Unfortunately, if we don't know the actual problem they're trying to solve, the answer we give may end up being totally unhelpful.

    What is far more useful is the statement of the problem, similar to that you gave in your second post. Whilst I (like @hevans1944 ) might not understand how a piece of paper moving through a slot like a moneybox would help a child "suffering from bad housing to feel more at home", I do understand ordinary paper and slots like those in money-boxes.

    Armed with that information it's a lot easier to recommend a solution. If you're going with an arduino and software, it isn't necessary to ask if the piece of paper is inserted or removed to turn on the light, and whether the opposite action will turn it off again -- all of that can be written into the software.

    I would note that if you're using an optical sensor, you're best off with an IR one because that won't produce a small glow when the light is off. Commercial units generally are IR, but if you decide to make one yourself from a LED and a phototransistor then this may be something to consider.
     
    hevans1944 and Harald Kapp like this.
  8. hevans1944

    hevans1944 Hop - AC8NS

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    @(*steve*), thanks for that post. Another person that I respect here PMed me with the admonishment that my first reply to this thread was condescending. Looking back on it, probably so, and I hereby apologize to @Katie Davidson Smith for that. Frustration is no excuse for a lack of temperance in my response. Perhaps I have become a crotchety old man, like Ed, the school bus driver guy in the Crankshaft cartoon panels. Example below:

    [​IMG]

    I sincerely hope I haven't driven the OP away with my curmudgeonly comments. It appears lately that everyone needs help understanding electrics. Same-o, same-o as when Tesla and Edison duked it out. Maybe Ben Franklin had the right idea after all: learn by doing... go fly a kite during an electrical storm to learn about electricity.
     
    Harald Kapp likes this.
  9. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    I found this instructable for a light that is activated by an LDR (light dependent resistor) when it gets dark. It's a neat little circuit that could do the job here. All you need is a light (LED) shining on the LDR, thus turning the controlled light off. When a paper is slipped between the permanent light and the LDR, the LDR gets dark and the controlled light turns on.

    Note that the controlled light will turn off once the paper has passed all the way over the LDR. If you need to have the controlled light on for some amount of time after the paper has passed the LDR, an additional monostable circuit needs to be included. This other circuit would be suitable. Simply replace the pushbutton by the BC547 transistor in the sensor circuit and remove the LED and the 1 kΩ resistor from teh sensor circuit (You could use this LED and resistor combo as the permanent light to shine on the LDR).

    Note that a 9 V battery will be drained comparatively rapidly. I suggest you use a wall wart or a pack of 4 to 6 AA cells (preferably rechargeable ones) for longer endurance. You may also want to include a switch in teh positive supply to completely turn off the device during the day to save energy.
     
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