WiFi and Bluetooth capable microcontrollers are very popular for hobby projects, but at the best of times offer a range of around a hundred meters. Indoors, with with walls and other obstacles, the usable range is often less then 20 meters.
A radio using a much lower data rate and frequency can achieve many kilometers of range1. The low data rate allows even a very weak signal to be received, and lower frequencies are much better at going through walls, trees and other objects.
(Wireless communication and power)
(Computer programming)
This article is not about any particular method of error correction, but about the general and rather simple principle that underlies all of them. The goal of error correction is to convey information as reliably as possible over a noisy communication channel using fixed power and time.
To make this more concrete, I will try to send a 10 bit message over a (simulated) pair of wires. The simplest scheme is to send 1 bit per second, a one as 1 volt, and a zero as -1 volts.
(Wireless communication and power)
There are a lot of cases where multiple devices have to communicate simultaneously over a single radio channel, or wire. Examples include mobile networks, 2 way radios, satellite communications and local area networking.
The simplest solution is to have the devices take turns, also known as TDMA (Time Division Multiple Access), but this requires precise synchronization.
Another is using a different carrier frequency for the device, effectively splitting the channel into many subchannels.
(Wireless communication and power)
The core principal behind most wireless power systems is electromagnetic induction, where current flowing through a coil generates a magnetic field, and a magnetic field generates current in a coil.
Induction can be used to transfer power wirelessly by placing 2 coils next to each other; When alternating current is applied to one coil, it creates an alternating magnetic field, some of which then passes through the other coil, creating an electrical current in the coil:
(Electronics)
(Wireless communication and power)
Variations of the “Cantenna” project have been floating around on the internet for a long time (mostly intended for 2.4 GHz WiFi). However, despite the abundance of calculator tools, there is a lot of conflicting information and very little in the way of explanations. I will try to explain how they work, the math for designing one, and provide measurements for 2.4 GHz WiFi 5 GHz WiFi, and a correct calculator tool.
(Wireless communication and power)
NFC smart cards are commonly used for a wide variety of applications including contactless payments, building access control, and 2 factor authentication. These smart cards have no power source, yet are capable of bidirectional communication, storing data, and performing cryptographic operations. In each of these cards is a circuit straight out of the 1900s: The crystal radio.
Most of the card is taken up by a flat coil, which can often be seen if the card is held up to a bright light.
(nfc)
(Wireless communication and power)
Here are the full schematics for a (slightly improved) FM bug and beacon with a class-C output stage described in the last post.
Bug:
Beacon:
The improvements consist of 2 modified resistor values, the emitter resistor on the oscillator stage (Not much power is needed for the output stage), and the bias resistor for the amplifier.
Together these changes allow the device to run 1.5x as long with almost no effect on output power, and run down to 2V with a reduced output.
(Wireless communication and power)
It is surprisingly easy to make a working FM transmitter with just one transistor and a handful of passive components.
This circuit runs best off single 9 volt battery (or another power source with the same voltage), but can function as low as 3v at the cost of output power and range. The coil should be 6 turns of insulated solid core hook up wire wrapped around a 3mm form (Thinner wire works but allows vibrations to effect it), and the antenna is 30-60cm of wire.
(Wireless communication and power)
A Crystal radio is a great project, with just a coil of wire, a diode, and a variable capacitor you can build a working AM radio. Unfortunately, getting any kind of sensitivity and volume with a Crystal set requires lots of effort and fine tuning, and even then, the sensitivity leaves a lot to be desired.
A simple form of amplified receiver, the regenerative set, requires only a single amplifying element.
(Wireless communication and power)