[0:00] A parcel has arrived.
[0:01] As someone who makes their living writing software, it’s sometimes the little things
[0:06] that give me pleasure.
[0:07] Somewhere, in a database far far away, I have an alter ego called null.
[0:12] So, what’s in the box - it’s super powers - I am now electro man and can turn on LEDs
[0:18] just by holding them!
[0:21] I actually saw these wireless LEDs on the Tested channel recently and decided that I
[0:26] just had to have some.
[0:28] Adafruit had of course completely sold out, so it was off to Aliexpress - I’ve put a link
[0:32] to the ones I ordered in the description.
[0:35] They look really great - it’s like having some gemstones in your hand.
[0:48] I’ve tested the vertical range from the centre of the coil upwards and I get around 10-11cms.
[0:55] This actually performs considerably better than the included datasheet - pretty impressive.
[1:00] As you’d expect the RED LEDs seem to have the most range due to having a low forward voltage.
[1:20] With horizontal range, I get around 7 and 9 cm from the centre of the coil. Which is also not too bad.
[1:43] As you saw earlier, the power can penetrate flesh and paper very easily.
[1:47] And they can actually get through pretty thick obstructions.
[1:51] Here we see them working through a copy of numerical recipes in C, and here we’ve stacked
[1:55] the algorithms book on top of that.
[1:57] That’s 3 and a half inches of dense material! And it still kind of works.
[2:02] So, how do they actually work?
[2:04] They are based around wireless charging technology, the actual LEDs are very simple, there’s an
[2:10] inductor and capacitor forming a tuned circuit around the frequency that is being pumped
[2:15] into the large coil.
[2:16] The LEDs are just placed across this LC circuit and if you are close to the power source there’s
[2:21] enough voltage induced to light up the LED.
[2:23] LEDs really don’t need much current so they’ll light up pretty easily.
[2:27] In theory, it should be really easy to make more of these LEDs - all you need is an inductor,
[2:32] a capacitor and an LED.
[2:35] Do you like PCBs?
[2:36] Do you want to make a PCB in a weird and wacky colour like Purple?
[2:40] Maybe you’d like a flexible PCB?
[2:43] Or maybe you’d like someone to do some CNC work for you - check out the link to PCBWay in the description.
[2:51] I’ve soldered a couple of jumper leads across one of the LEDs so I can connect it to my
[2:55] oscilloscope.
[2:56] You can see here that we’re picking up a frequency of 217kHz, the LED is clipping the signal
[3:02] at just around 2volts - this is the forward voltage of a green LED.
[3:07] If I add a red led in parallel with the green LED I can use the negative part of the waveform
[3:12] to drive it - we now see that the negative peaks are clipped at around 1.7 volts - this
[3:17] is the forward voltage of a red LED.
[3:20] Of course, if you put the red LED in the same direction as the green LED then you only see
[3:25] red as its forward voltage is lower than the green led.
[3:29] Looking at the trace of the signal going into the coil we see this waveform - which is interesting
[3:34] as I was expecting to see a sine wave - if anyone knows why the signal looks like this
[3:38] then please let us know in the comments.
[3:42] The chip that is doing all the work is an XKT-333 - I couldn’t find much information
[3:48] on the internet apart from this Chinese datasheet which doesn’t really tell you very much.
[3:53] I’ve had a go at reverse-engineering the PCB - it’s pretty simple - but I’m no Big Clive
[3:58] - so take the following with a hefty pinch of salt.
[4:01] I’ve labelled up the traces, there is a component that I’m not sure of, but I think it’s an
[4:05] adjustable regulator feeding the XKT-333 2.2volts.
[4:10] Here’s the schematic that I’ve reversed enginerred for the circuit.
[4:14] We’ve got an input capacitor, followed by the regulator and its resistors.
[4:19] This feeds into the XKT-333 which controls one end of the coil and capacitor.
[4:24] The other end of the coil and capacitor is connected to the 5v supply.
[4:29] I believe that all that happens is the XKT-333 is periodically connecting the coil to ground.
[4:35] And that’s what’s creating the signal that is driving the whole thing.
[4:38] I’ve got a couple of other wireless chargers in the house so I thought it would be interesting
[4:43] to see if they can drive the LEDs.
[4:45] It’s a very interesting result - I assume this pulsing is used by the iPhone and Apple
[4:50] watch to detect an official charger - or maybe it’s some kind of power negotiation, either
[4:55] way, it’s pretty bright, so it’s obviously putting out a lot more power than the coil
[4:59] I have from Aliexpress
[5:01] It’s all pretty interesting stuff - now I need a project for these LEDs - suggestions
[5:08] in the comments please!