Motion Activated LED artwork

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rcane

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Specifications

The motion sensor will pick up on nearby hand movements through a small hole (≤ 1mm diameter)

Each panel will have LEDs behind it with 30mm spacing in each direction of the LED (looking like graph paper)

I am a sixth form student, and have no prior knowledge of electronics, but I have practiced building circuits to instruction and am able to solder to a good degree of accuracy. So assembly shouldn't be a problem.

What I need to know, is exactly what I may need to make the circuit work. It will run using mains electricity at 240v, so I assume I will need a transformer to step this down. Also, I would like to know if each separate LED needs a resistor, and how to work out the values of the resistors I may need. For a typical small panel, the number of LEDs used will probably be around 12. For a large panel, this number could be increased to around 50. I anticipate using around 500 LEDs overall.

I appreciate that this is a difficult assignment, so any help you guys can offer me will be highly appreciated.



Where do I start?
 
Welcome to electro-tech-online, rcane!
I once built a simple motion detector circuit that ran on 5-15 volts dc that detected changes in the amount of light the circuit received. It used an LM393 comparator chip (could also use a 358 op-amp) and a CdS photoresistor to sense even a very slight shadow and turn on the output from a 555 (depending on what you want the LED array to do after being triggered). What are you planning for the LEDs? Do you want them to stay on after they are triggered until someone resets it, or do you want them to stay on for a certain amount of time and shut off on their own?
If this is what you're looking for, I can try to post a schematic for you.
Good luck, and keep posting!
Der Strom
 
I would start with your power supply. Make sure it is powerful enough to power your LEDs and your sensor circuit. If you use an LM393, or it's quad cousin the LM339 then your supply voltage can go up to 30V without any problems at all (just remember most comparators can't source any current). 500 LEDs is quite a lot to use so make sure your transformer is capable of putting out enough amps to drive all of those LEDs (500 20mA LEDs would need at least 10A to drive all of them). This comes out to a primary fuse of about 1.5A if 30V is used.

You can use a photo-diode, photo-transistor, or a photo-resistor like DerStrom suggested. You can connect it to a comparator that references the average of all the other photo-sensors to decide if there is movement, or if it is just a change in light. A photo-diode would be the best because it can be connected to an op-amp before going into a comparator and all of those voltages can be combined to make an average of the light level. If you plan on using one photo-sensor for each LED, then you will need a lot of summing amplifiers.

If you plan to have your LEDs flash when they sense motion, then it is a good idea to use the sensing comparator as an oscillator. If you go to Google and type in "LED Coffee Table" then you get some pretty interesting results that look similar to what you are trying to do. If you want your LEDs to stay on dimly, then you should try using an op-amp configured as a comparator.

To find out what resistor size you need for your LEDs is quite simple. The equation is given by: Supply voltage-LED forward voltage/ LED current. Just remember that your Resistor needs to be able to dissipate the power that it will be given, or else it could catch fire (this happened to me once and was not fun to put out). If you have an independint resistor for each LED then the brightness will depend strictly on what the output of your sensor is. If you use one resistor for all of the LEDs then as one dims, the rest will get brighter because of ohm's law.

Hope this helps,
Vince
 
Yeah, that LED coffee table would almost be perfect. The idea behind it certainly is.

Basically, I need the circuit to be simple enough for me to build it without tooooo much hassle, and for the motion sensor in the pinhole to be wave once to turn it on, and wave again to turn it off. Obviously I'd prefer it if the waving action could be within an inch of the panel, like the coffee table, so you can't set them all off at the same time by accident. Also, they don't need to do anything special, the LEDs just need to turn on and off.

So, you're saying that I am going to need to have all of the different boards wired together, and use one chip right at the beginning to make sure that it's not underpowered? Or would it be easier to use different boards all wired to the same transformer(if that's even possible haha)?

As you can see, I have no idea. Building this circuit will also require the expertise of a teacher to tell me where stuff should go.


LM339 Quad Comparator [RC] ----- that one?
 
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Yes, that looks like the right one.
As for the wave-on, wave-off, you will need a circuit like this one, connected to the sensor circuit:


I believe that if you replace SW1 with a bipolar transistor (collector to "clk" and emitter to "0v"), the base can be connected to the output of the sensor circuit. This way, it will turn on when it receives a signal (a wave) and turn off when it receives another signal (a second wave).
Good luck!
Der Strom

EDIT: I believe you will actually need a PNP transistor for this part of the circuit, so that it can be triggered by the 393. I this case, you will need to connect the emitter to "clk" and the collector to "0v".
 
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Haha, that schematic confused me but I'll have my teacher go through it with me if he can remember it. If not I'm sure my physics teacher can help me out, he loves electronics. Thanks for your help so far!

I get the feeling this project might be over my head at the moment, but I'm gonna persevere because if I make this work, then I'll get an A grade, which is something I really need!
 
By all means, keep going! I'm sure you can do it!
I have the schematic for the original sensor circuit, but I'm pretty sure it can only be opened in ExpressSCH (the program that I used to draw it). I'm not sure how to post schematics I've drawn out straight to the forum :/ If anyone can give me a hand with this, it would be greatly appreciated!
Anyway, the output in my schematic is connected to an LED. If this was connected to the transistor, mentioned in my previous post, it should work to wave-on, wave-off.
Keep up the good work!
Der Strom
 

A quick note: I think this schematic is mislabeled, namely at the very bottom it says +5v. I don't think this is right. Though I could be wrong, I think that should be 0v (ground).
I have put together the circuit schematic that I think will work for your project, but I'm still not sure of how to post it yet. Can anyone help? Thanks a lot!
Der Strom
 
I'm gonna take the schematic you gave me in with me on Monday, so I'll see what's said. I think it'll be plausible, I just need to know where stuff is gonna go, but that's down to me isn't it?
 
Absolutely
Now, just out of curiosity, would you happen to have ExpressSCH on your computer? If you do, I can post the whole circuit, to give you a good place to start.
 
Sorry for the late reply here, I don't have it but I can definitely get hold of it. A schematic would definitely help me
 
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