Contactless key

In this article I will tell you about how to make a simple and reliable contactless key.

To begin with, I’ll explain what this key is, the bottom line is that there is a transmitter on the battery and a receiver built into the device we need, we bring the transmitter to the device, and it starts to work. The big disadvantage of our installation is the range, it is about 5 cm.

Before assembling the device, consider the circuit

Transmitter.

It is a conventional high-frequency generator (HHF) based on a block generator. I used the KT930 transistor, and the KT315 and all other npn transistors of the 3,6,9 series are perfect, basically they are all generator ones. You can feed the circuit from a 1.5 volt battery, but the higher the supply voltage, the greater the range. Another drawback of this scheme is that the transmitter starts only after briefly shorting the base and the collector, but it is not difficult to make the start button.

Receiver.

The L3 coil resonates with the transmitter, as a result of which an alternating current is induced in it, which is rectified and opens the transistor T2 (MP20OS) and, by means of all these frauds, relay K1 is activated, to which anything can already be connected.

Enough theory, let's move on to practice.

Here is the necessary set of parts

And another relay.

We will also start the assembly with the transmitter, first we wind the coil, take a round frame with a diameter of 5 cm and wind a wire with a diameter of 0.1 to 0.6 mm on it, the thicker the wire, the greater the current consumption.

for L1 and L3 60 turns for L2 30 turns. After that, we solder the windings according to the scheme with a transistor and put one on the other

And we get a rather interesting installation, if you connect an LED directly to the L3 coil, you can get an amazing effect, this can even be called wireless energy transfer.

In the same way, you can check it, if it doesn’t work, repeat, close and open the collector and base or turn over one of the windings of the transmitter, just take it by hand and turn it over. The same field pierces 338 sheets of glossy paper

Therefore, the receiver can be easily hidden in the case of any device, only the case should not be of metal

That's all there is to add a relay and electronics.

There are many applications of this device that can be built into the PC case; it is only advisable to shield the receiver from the motherboard, this can affect the operation of both the receiver and the computer. I think the application for such a device will definitely be found. If not, you can leave the LED to fix the transmitter, for example, under the table, and putting the receiving coil on the table will also be a very funny device.

Wishing to repeat good luck!

P.S. video with a visual demonstration of the receiver and device operation