In this video I'll show how I built a remote control that works entirely off the magnetic field of a coil (unlike a typical radio transmitter). This is known as inductive coupling, an is the same principle used in a transformer. The only difference in this case is that the windings of the transformer are very far apart. This type of signaling is common in short-range, low power devices, like RFID.

This is effectively the same setup that would be used for wireless power transfer, but with two key differences:

-The output of the transmitting coil is not a continuous wave; it's modulated to produce a signal

-The signal of the reciever coil is amplified (by about +70 dB)

The transmitter produces a series of damped oscillations at 69 kHz, with a pulse frequency that can be varied between 1.3 kHz and 2.3 kHz.

The reciever circuit the same design as you'd find in a simple AM radio, the only difference being that the frequency used here (69 kHz) is far below the AM band. The reciever extracts the signal tone, and cleans it up through a schmitt trigger to produce a 0-5V square wave. The schmitt trigger output is sent to an Arduino Uno, which reads the tone frequency, and controls a standard R/C toy servo accordingly.

The main advantage of this kind of transmitter is that it can be made to work without the huge antennas or elaborate grounding schemes needed to operate a typical ULF/VLF radio. The disadvantages are that it's very directional (on both the transmitter and reciever end), and the signal amplitude drops off exponentially faster than a typical radio. With an ideal omnidirectional radio transmission, the amplitude drops off with the square of the distance, whereas with inductive coupling, the drop off is approximately the 3.5th power of distance.

Relevant components in these circuits:
-IRLZ44 MOSFET
-NE555 Timer
-2N3904 and 2N3906 NPN and PNP BJT's
-1N4148 Diodes
-LM7805 for 5V Regulation
-15 to 365 pF Variable Capacitor for Reciever Tuning

https://www.amazon.com/Capacitor-Vari...


Music Used:

Kevin MacLeod - Groove Groove
Kevin MacLeod - George Street Shuffle
Heatley Bros. - Otherworld
Lukrembo - This is for you