This reverse engineering of the 125 kHz RFID reader was done in my leisure time and then I used it as a part of another project – an RFID Access Control. The hardware prototype of the project was tested by using the newest version of the EM-18 RFID Reader Module, after testing various versions of EM-18 available on the market.

This version of the EM-18 – with white PCB inside – uses STM8 microcontroller instead of ATtiny2313 – widely is used in other versions – and needs fewer components, which leads to a cheaper device. It is also faster, and can detect cards and tags from longer distance than the older versions and other similar reader modules.

The firmware was developed for STM8003F3 – same as the module – in IAR, implementing EM4100 protocol and Manchester (G. E. Thomas) decoding, after obtaining the schematic of the module and analyzing the circuit. This piece of circuit was added to the main project in order to embed its implementation, reduce the product cost, and solve the size issue.