L1 is driven via a low-impedance 125 KHz oscillator, can be a sine or a square wave So this configuration is probably one of the simplest forms of an RFID reader-tag pair: Since my chosen frequency was 125 KHz, my capacitor should be 1.62nF according to the following equation I picked 1n5 standard value. I’ve used a coil of about 1mH for both sides. I first started by creating a simple, non-filtered, non-processed reader.
Morse decoder source code parallax verification#
The data verification is been done from ATtiny13 by calculating the Even parity bit of each line and each column with the parity bits that had been received form the RFID Tag transmitted data. The PC1, PC2, PC3 bits represent the parity bits of the next 3 columns.The PC0 bit is the Even parity bit of bits D00, D04, D08, D12, D16, D20, D24, D28, D32 and D36 (the bits on the same column).
Morse decoder source code parallax serial number#
The next 4 bits are first part of the 32-bit Tag's serial number (D08.,D11).The next 1 bit (P1) is the Even parity bit of the previous 4 bits.The next 4 bits are the High Significant Bits of the customer ID (D04.,D07).The next 1 bit (P0) is the Even parity bit of the previous 4 bits.The next 4 bits are the Low Significant Bits of the customer ID(D00.,D03).The first 9 bits are the start communication bits ( always '1' ).The data transmission from Tag to the reader varies from 500 bits per second up to 8000 bits per second. The 'Ones' or 'Zeros' length depends on the serial transmission data rate.įor example, for 125 kHz carrier frequency we don't have 125000 bits per second data transmission! When the Tag doesn't require any additional power, it doesn't make a voltage drop.
When the Tag drops the voltage as we said before, the reader reads this voltage drop as logic '0'. Simultaneously, as long as the reader transmits the 125 kHz signal it reads the voltage of the transmitted signal trough the filters D1, C3 and R5, C1. That voltage level is logic '0' (picture 4). That will make a small voltage drop on the RFID reader side. When a Tag wants to send a logic '0' to the reader it puts a "load" to its power supply line to request more power from the reader. How an RFID Tag communicates with the reader? These transitions of L1 to logic '1' and logic '0' are made 125000 times in one second (125 kHz).ĭata communication between Tag and reader. The L1 goes in parallel with C2 creating an LC oscillator.
When PB0 pin rises (Logic '1') the T1 conducts and one side of L1 goes to GND. So the L1 is energized from R1 (100 ohm) with +5V. On the falling edge of the PB0 (Logic '0'), the T1 does not conduct. The ATtiny13 uses the PWM function to produce an 125 kHz square wave signal. I will try to explain with simple words how the RFID works.