RFID Reader

A not so simple 125KHz rfid reader based on a ATTiny and EM4095

Build around a single timer (Timer0), uses two interrupts pin change and INT0 Manchester code decoding based on Timing approach. Base clock 16.5MHz.

Input

• PB2 - Input of Card data (after EM)

Outputs

• PB1 - EM4095 disable / Red led
• PB0 - Green led

Quite interseting

This device tries to calibrate itself to 16.5MHz by measuring usb packet lenght. It also stores its last calibration value to EEPROM byte address 0 (first byte as this can be read by avrdude)

Also never compile this with optimization level -O3 as USB will not work. -Os (size) seems to be ok

Makefile

For convinience there is a make file with instructions:

• make - compiles the compileables
• make flash - flashes flash with a flash file
• make fuse - tries to fuse the fuses
• make install - compiles, flashes, fuses

PCB

Double layer SMD in KiCad format

AVR Memory Usage

Device: attiny85

Program:    2456 bytes (30.0% Full)
(.text + .data + .bootloader)

Data:         70 bytes (13.7% Full)
(.data + .bss + .noinit)

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Thanks to:

• Vassilis Serasidis - Manchester code ideas
• V-USB - Software USB support :)