Hey, for a bigger art-project I want to build some wireless LEDs like here:
The LEDs (receiver) are simple, but the sender circuit is a bit much. I will need around 20-40 of the Senders and 100 Leds 
Is it possible to replace the ESP32 with an i.e. 555 or something else? Would be nice if the circuit in the end is as simple as possible.
Also one more question, does someone know why they use a 40% mark to space ratio?
Is someone so kind and can help me with that? Thanks in advance.
Can you tell more about the project ?
I doubt if this is reliable enough for your project. It seems to be just a quick project with minimal components.
Do you know if it is legal ?
The ESP32 has the advantage that the frequency for the coil will be the same.
For the circuit I would use a full or half H-bridge with 50% duty cycle.
I don't know why he uses 40% on and 60% off, perhaps it has to do with the circuit.
Adafruit sells a small version and a bigger version.
I think that X-Base started a Kickstarter in 2017: https://www.kickstarter.com/projects/1294229783/x-base-wireless-led-lighting-and-display-system
Its something like a ...hm.. Magic Library with some Magic Books and other Artefacts. The should be useable and when they are back on the place where they belong (or a Magician comes along with a hidden coil) they should light up. I dont have much space in the Books and Artefacts.
Yeah you can also buy them on Aliexpress, but I will need sometimes some modifications and so its better to diy. (bigger/smaller coils... Leds to the side ... and so on)
It already feels unreliable and a 555 makes it even less reliable.
To use a 555, you need a voltage that is fixed (not from a battery) and good components. The 555 can do a frequency between 200kHz and 300kHz, that is no problem.
The frequency of the receiver coil will change with metal nearby, or a hand nearby.
If you can find out of it is legal, then you can order an existing version to try it out.
In my opinion, it seems a gimmick for something static to look at. You have to test if it is reliable enough for your project.
Can you modify existing wireless leds ? They have already found the optimum for frequency/costs/reliability.
already ordered to test out, but I really wanna try to build some myself.
Legal? I really dont know, dont even know where to ask.
Nice project!
Have a read of this:
You could build an oscillator around the driver coil following the guidelines in that tutorial. There is lots of other information if you search, I searched for LC oscillator.
If you're responsible enough to build a transmitter, you're responsible enough to understand the EMI regulations. But since you're new, if the circuit is really on 225 kHz and you don't generate too many strong harmonics of that, you should be okay.
Having said that, the driving circuit is pretty crude class A amp.
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