In this library I’m talking about RFID (Radio-Frequency IDentification).
Radio-frequency identification (RFID) is the wireless non-contact use of radio-frequency electromagnetic fields to transfer data, for the purposes of automatically identifying and tracking tags attached to objects. The tags contain electronically stored information. Some tags are powered by and read at short ranges (a few meters) via magnetic fields (electromagnetic induction). Others use a local power source such as a battery, or else have no battery but collect energy from the interrogating EM field, and then act as a passive transponder to emit microwaves or UHFradio waves (i.e., electromagnetic radiation at high frequencies). Battery powered tags may operate at hundreds of meters. Unlike a barcode, the tag does not necessarily need to be within line of sight of the reader, and may be embedded in the tracked object.
For that usage, I used Mifare RC522 RFID reader from NXP. I got it on Ebay almost for free with 2 RFID cards included. This chips works with RFID on 13.56MHz. To get this to work, you also need RFID cards with same working frequency (included in packet from ebay).
I got this working on STM32F429 Discovery board with SPI communication and display data on LCD on board. Detection distance was about 10cm from receiver.
Finally I got it working properly. Reading SDcard was very awesome for me for first time, so I decided to make a library for STM32F4xx devices and post it to my website. It’s basically just communication interface between STM32F4xx and FatFS library by Chan.
It’s been some time when I post last library. Next one is internal RTC library. STM32F4xx devices have Real Time clock inside, with support of internal calibrated 32768 Hz oscillator or external (more accurate) 32768 Hz oscillator.
RTC peripheral has also backup register support, which means that when you reset MCU, registers are not reset or if power is off and you have battery connected on Vbat pin, clock is still working.
RTC can also wakeup MCU from all powerdown modes.
Library also provide converting time to epoch time (seconds from 01.01.1970 00:00:00) and back.
Support Internal or external clock source
PC14 and PC15 pins are used for external crystal oscillator
STM32F4/24 Discovery does not have RTC crystal onboard. Check board’s manual on how to set it up
Support wakeup interrupt
Get seconds from 01.01.1970 00:00:00
Get readable time from seconds from 01.01.1970 00:00:00