RFID Stands for Radio-frequency identification.
It uses electromagnetic fields to automatically identify and track tags attached to objects.
I've never worked with frequencies above 20khz as I'm always working on audio circuits.
so I did some research, asked few people and searched on the internet.
First of all, you have to know that mainly there is two kind of RFID systems.
1.Active 2.Passive
1. Active tags have a local power source (such as a battery) and may operate hundreds of meters from the RFID reader.
2. Passive tags collect energy from a nearby RFID reader's interrogating radio waves.
First, I decided to go for the active one as it's working with an external power source and it can work at long ranges.
All RFID systems contain receiver and tag.
I decided to build the receiver first and go for the tag after that.
as I didn't know anything about rf circuits I did some search on the internet for some active RFID receiver circuits and BOOM.
the active receiver circuits were really hard to build and the components were hard to find and forget about the tag part.
Plus, this kind of systems is getting used at big factories and mainly they are using it to transmit sensor data and .....
so I decided to go for the passive one because I'm a Genius.
There are 3 types of passive RFID systems.
LF Passive < 135 kHz
HF Passive 13.56 Mhz
UHF Passive 868 - 950 Mhz
(this one is active)
UHF Active 433 - 5.8 GHz
(you can find more data about differences in range and frequency at the table below.)
there is plenty of passive receiver circuits on the internet , and all of them works almost in the same way.
there is a Carrier wave oscillator which is made using LC circuit.
An LC circuit, also called a resonant circuit, tank circuit, or tuned circuit is an electric circuit consisting of an inductor, represented by the letter L, and a capacitor, represented by the letter C, connected together. The circuit can act as an electrical resonator, an electrical analogue of a tuning fork, storing energy oscillating at the circuit's resonant frequency.
in order to transmit information trought air using electromagnetic wave, we need to modulate the signal using a carrier signal..
In telecommunications, a carrier wave, carrier signal, or just carrier, is a waveform (usually sinusoidal) that is modulated (modified) with an input signal for the purpose of conveying information. This carrier wave usually has a much higher frequency than the input signal does. The purpose of the carrier is usually either to transmit the information through space as an electromagnetic wave.
How LC tank circuits work?!
Well LC circuits need square wave at their input to keep resonating .
for this project we need 125Khz square wave to feed into LC circuits witch it's component values is tuned to 125Khz too.
to give you an example i'm going to show you a simulation that i made using circuit simulating software.
as you can see I'm using a series LC circuit, feeding it with a 0-5 V square wave with the frequency of 125Khz and with the inductance of 220uH and capacitance of 7.37uF the resonating frequency is tuned to 125Khz so the voltage is building up around 120V pick.
this kind of tuning is a bit hard in real life but it's possible.
so this is gonna be our carrier wave, a pure sin wave with the frequency of 125Khz.
I used an online inductance calculator to be able to build my coil, you can find one of them online easily or follow the link below :
(i suggest you use thin wire)
for square wave source, I used an Arduino UNO PWM output to generate it.
when it's all done, and circuit starts to work there will be electromagnetic wave around the coil and on the other hand we got passive tags which are made of two parts, a coil, and a small microcontroller.
when the tag is near the receivers coil it acts like transformers secondary and the magnetic field of receivers coil passes through tags coil and generate current inside the coil, this power is enough to run the tags microcontroller and sends some data using its coil to receivers coil.
then at the receiver, this modulation can be detected using a simple envelope detector circuit as a voltage drop and .....
the rest of the process is dc coupling and amplification of the signal in order to feed it back to the same Arduino Uno to read the data and ID of the tag.
If you are professional and got some measurement instruments like Oscilloscope, frequency counter and... I suggest you follow this link and build this receiver circuit.
but if you are not so professional or you don't have enough gear to fine-tune the circuit and LC tank, then I suggest you go for chip kits like this one:
rdm6300 RDM6300 125Khz RFID reader
it's pretty chip and really easy to set up, just connect the antenna , connect the pins to Arduino and upload the code and you're ready to go.
it's possible to monitor the data using Serial Monitor or Arduino IDE or use an sd card to save data.
Follow the link below for pin diagram and Arduino codes:
https://www.mschoeffler.de/2018/01/05/arduino-tutorial-how-to-use-the-rdm630-rdm6300-rfid-reader/
Passive Tag:
You can easily build a passive tag using few passive components like coils , capacitors and an AVR microcontroller , there is plenty of projects in the internet to build this kind of tags like this link below :
https://scanlime.org/2008/09/using-an-avr-as-an-rfid-tag/
But again i suggest you to buy chip tags like this:
Building tags is fun but for me it turned out to be a little bulky and not good looking while this 1$ tags is really small and chip.
Passive Tag:
You can easily build a passive tag using few passive components like coils , capacitors and an AVR microcontroller , there is plenty of projects in the internet to build this kind of tags like this link below :
https://scanlime.org/2008/09/using-an-avr-as-an-rfid-tag/
But again i suggest you to buy chip tags like this:
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