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A very simple project that allows you to pulse LEDs with no wiring or battery.
The project uses a QI wireless charger to power some LEDs with nothing more than a coil of wire.

This video involves strobing and flashing lights. It's showing how to make a very, very simple coil, with two leds and a coil of wire to take power from a qi wireless charger and use it to flash the leds. The reason leds are flashing is because this device won't put out continuous power until it gets communication back from whatever it's charging. So because these can't provide that communication back.

It simply keeps pulsing them and it makes them flash like little strobes, which is quite nice in its own right yeah and could be used in some instances to provide just enough power to trickle charge, something without any fancy circuitry. So i'm going to show you how to make one of these and you've got a choice. You can either use standard wire like this. This is just 10 turns, or you can use the enameled copper wire not going to use the enameled cover bar so before i actually make it i'll show you.

What this is going to involve here is the circuitry. It's very simple: it is the 20 turn coil and then two leds in inverse parallel. The reason they're in inverse parallel is because, when current is being induced in the coil, it will be both polarities and i'm not sure what the open circuit voltage of that is. So to play safe, i put the leds in the other direction, which means that each will clamp the voltage across other and prevent overvolting the leds, the gallium nitride leds, the brighter colors are very prone to damage with uh two higher reverse voltage.

So we're going to take an led and we're going to bend the leads down sideways on it. We're then going to get the two of them and line them up in a bit of a white tack or blue tack. So the long lead points to the short lead and the long lead here points the short lead over there and that will effectively wire them in inverse parallel. Let's do that, so i've got a couple of leds here, i'm going to fold the leads down and then i'm going to stuff them into that blue tack.

I shall zoom down in this when i so do this. So here's the first one being stuffed into the blue tack and then i shall match the alignment of the lead to the other one so that the when i fold it over the short lead connects the long lead i'll zoom down for this right. Now. That's that's a good idea, so i'm folding these leads over and now i'm going to line them up in the plasticine blue, tac play-doh or whatever you have or white tack.

In this instance, it's probably not real white tack. It's probably a clone. I'm going to bend those leads just to make sure everything lines up perfectly and then i'm going to throw some solder onto those here is my solder. I've seen other people making these, but they only use a single led, and there is another technique that uses a couple of diodes: a capacitor and a single led which basically rectifies it and doubles the voltage.

So that's those uh connected together now in inverse parallel. Let's make the coil and for this i'm going to be using this enameled copper wire. This is from maplin in the past uh 0.315 millimeter. That just chose a random value.

I'm going to zoom out for this because i think it'd benefit from being just a little bit further out. I'm going to use i've tried various diameter coils. To be honest, i found the smaller ones were pretty good, so this is a piece of standard british 22 millimeter plumbing pipe water pipes. That's one two, three, four five! You don't have to be too neat about this six.

Seven, eight, nine. 10. 11. 12.

13. 14. 15, 16, 17, 18, 19 and 20.. You could experiment with the number that you use.

I just arbitrarily chose 20 after trying the 10 with the thicker wire, the it kind of because of the uh bulk of this standard stranded wire. It tends to pack it out. Quite quickly, it tends to make quite a big coil, so i'm going to cut this off and then i'm going to carefully slide this off, noting that it will want to do its best to be a slinky and suddenly explode into separate spirals. It may do that right now, so i'm just carefully winding that out, while holding it together and then to hold the turns in place, i'm actually going to use the wire itself to just put a couple of loops around.

For some reason. This has reminded me of a rogowski coil, a very specific type of coil used for a single ended. Current sensing transformers and some industrial measurement applications now bring those leads out parallel and i'm going to zoom back in again, because i'm going to be soldering these to show you how to effectively strip the ends easily. Well, i'm not really stripping the ends, so this is enameled, copper, wire and all i'm really going to do.

Is i'm going to get the soldering iron in and i'm going to float some put it under the wire and i'm going to flow some soda on and then just basically slide it backwards and forwards in that, hopefully, depending the type of lacquer used, it will tin The end it'll actually melt the insulation off the other options. You have are to use a a flame to do that, and also a mild abrasive or a sharp knife to just gently scrape it off now. I've beard that, where are my leds, i shall solder it to the leds. First, this side just reflowing the solder briefly, then let it cool so it doesn't move.

If you went straight over to other side, it would potentially desolder the leds from each other completely. When you re-melted the sword on the other side and that's the second side done and theoret note, let's, let's be more patient, see exactly what i said there about not being patient, let the soda cool and sad and harden without blowing on it. So now, theoretically, this is going to be a little blue strobe. It is it's a quite a bright blue strobe, that's quite nice, but that is it.

You can experiment, you can use multiple coils, but after a point it gets a bit miffed about the load and it will start uh flagging up. It's detecting a sort of inductive short circuit and it might start just strobing them. It's doing. Okay, so far see some of them are pulling the voltage down with the coils and actually sort of effectively screening the other one.

Now there's another thing can do these it may or may not work, i'm going to have to turn the light off for this one. So i'm turning the light off and i'm going to take the exposure off and i'm going to bring my phone in and i'm going to unlock it and at this point in time the near field communication coil on the back is active depending on the coil. You use you'll, see it pulsing uh, it's actually looking for something in the vicinity and it wouldn't do all the time it will generally detect the movement it'll. Do it occasionally or i'll detect movement of the phone, then it will do a few bursts to these pulses.

I had no luck with uh the others doing this now. Did i have any any of these coils? Do it nope? It only seemed to be that one with 10 turns. Maybe the higher number of turns is just uh or the higher voltage. The leds is an issue, but it didn't seem to work with others, which is a shame really, but that's okay, but it does work.

This is gon na, be so bright. Yeah super stroboscope see that's our wardrobe. At the beginning, it's going to be super bright right. The light is coming back, watch your eyes, not that your eyes haven't been fried by my disco, strobe as it is, but there we go it's a very silly sort of simple project.

You could uh make ornaments out of this, and you know how mcdonald's rush. I don't know if it's the same around the world, but they have these uh inductive charging pads built into the tables at mcdonald's. So it means you could make a little ornament uh and when placed on it it would strobe and pulse, and if you wanted, you could apply a little sort of rectifier, discrete rectifier um. This will be fairly high frequency, but uh you could make a little rectifier and a capacitor and it would charge it up and it would actually make the leds light continually.

But that's just another thing: it's quite fun. Actually, as you can see, i've been making quite a few coils, but there we go the chi strobe um yeah, pretty neat um. This uh larger coil is no better than the smaller one. I'm surprised by that i thought the bigger was going to be better, but it turns out this little 22 millimeter, which is just under an inch uh, is absolutely fine.

Actually, if anything, it looks as though it's really driving the leds quite hard, but there we go. How to make your own little mcdonald's table strobe! That's powered inductively from those coils.

18 thoughts on “Easy diy wireless strobing led light”
  1. Avataaar/Circle Created with python_avatars kasami's memes says:

    Putting one of those on a phone gave me an idea. An app running as a background service could monitor for incoming calls and trigger a whole bunch of NFC scanning or something, making it work like one of those old phone stickers you showed last week but for modern phones. The circuit could possibly also have something added to mask off the regular scan pulses so it's not flashing all the time, or the app could just turn NFC off if you don't need it for other stuff.

  2. Avataaar/Circle Created with python_avatars Brian Clark says:

    Hey! I take the inductor coils and other tiny coils off of motherboards and attach an led to the ends of the wire. It usually makes it flash on a qi charger but the coil size makes the brightness vary. I havent had any break yet.

    It also makes different patterns depending on the charger. Some strobe, some do bursts of multiple blinks.

  3. Avataaar/Circle Created with python_avatars Paul Drake says:

    Haven't seen any inductive chargers in our fast food joints but most of them do offer a standard USB jack at the table. No doubt there is potential there for making some entertaining, annoying or scary gizmos – a black box with an ominous count down timer comes to mind…

  4. Avataaar/Circle Created with python_avatars Simon Wilkinson says:

    Clive Maplin are back but only online….at this point they dont seem to have as much as in the past and appear a little expensive.

  5. Avataaar/Circle Created with python_avatars Mark Durbin says:

    Nice idea. If you bring the phone in while the coil is on the pad does it turn them on continuously? if so, does it stay on when you take the phone away?

  6. Avataaar/Circle Created with python_avatars Hola! White Gold WarRobots says:

    Hi BigClive. I watch your videos every often. These brings great Knowledge and inspiration to me. Man when I see this soldering iron and those screw drivers in your hands, I wish I could have them too but unfortunately I'm in Pakistan and can't have them.

  7. Avataaar/Circle Created with python_avatars ottard says:

    Both LEDs appear to light at exactly the same time, enen in 0.25x speed. How can that be, with such a slow pulse?

  8. Avataaar/Circle Created with python_avatars Ian Rolfe says:

    "Grandadisanoldman" has been playing with these charging pads the last couple of weeks.. He used chokes recycled from CFL tubes instead of hand-wound coils, and seem quite effective.

  9. Avataaar/Circle Created with python_avatars Personious k says:

    Not sure if this is up your alley, but my new dash cam is always plugged into power(through the fuse box), has GPS and wifi. Have any idea what stays on when the vehicle is turned off? Did I just tracking beaker myself?

  10. Avataaar/Circle Created with python_avatars Alex Mac says:

    . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I regularly charge my toothbrush on MacEE'D's table tops. . . . . . . . .

  11. Avataaar/Circle Created with python_avatars White Sapphire says:

    And that, boys and girls, is how we we get free electricity – We nick it from someone else's table!

    Yeah, I like that, and in its own way, it's not unlike those self energised mobile phone stickers you showed us a couple of videos ago. A modern take on walking about under the overhead power lines with a fluorescent tube in your hand?

  12. Avataaar/Circle Created with python_avatars mikeselectricstuff says:

    If you put a capacitor across the coil (probably 1-10nf) so it resonates with the Qi charger frequency, it will work at a much longer range – may also work better with one LED as this lets the resonance build up more over the previous half-cycle

  13. Avataaar/Circle Created with python_avatars Barrie Shepherd says:

    I would expect the closer the tuned value (or harmonic) of the coil/LED network is to the operation frequency of the charging pad (I think it's in the range ~100-200 kHz) the more energy would be transferred and the brighter the LED's. Maybe the main difference between the 10 turns and 20 turns coil

  14. Avataaar/Circle Created with python_avatars Gadgetboy says:

    Second thought. Could you put a small lithium cell in there (like those ones you've been scavenging)? Charge it off of the pulses?

  15. Avataaar/Circle Created with python_avatars James Hough says:

    I did notice the green one on your phone let out the few pulses, but after that i could still see a faint green glow, Was this just misalignment, or something else?

  16. Avataaar/Circle Created with python_avatars No no says:

    I just bought a premade batch of LEDs and the transmitter from adafruit, and was also wondering what to do with them.

  17. Avataaar/Circle Created with python_avatars Dom Wright says:

    Nice one. I bought a couple of cheap QI charging adaptors that work with most phones. They have a micro USB plug on the end. I used it to power a Raspberry Pi Pico.

  18. Avataaar/Circle Created with python_avatars ESC crasci says:

    This reminds of a small circuit I made where I made a guitar shaped PCB and wound copper wire around it (2000 turns) and soldered 2 smd leds to the end and later potted it in hotglue. Yours has turned out far better than that even with no resin. Mine was made a few years ago when I was still a starter in electronics (still am, but a tiny bit better). The blue tack tric is also really neat since all people don't have helping hands. And mine used both LEDs in parallel so it only turns on every half cycle of the output AC just like in yours.

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