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