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How Frequency Counter Works? And Build a Nanocounter using an FPGA, STM32 and a Bluetooth Android App

How Frequency Counter Works? And Build a Nanocounter using an FPGA, STM32 and a Bluetooth Androi ...

The MCU

The MCU that I’ve selected for this design is the STM32F072CBT6 in a 48-pin LQFP package. The 48-pin package gives me just enough I/O to complete this design and this 072 model comes with 128kb flash and 16kb SRAM. The large flash space was the key reason for the selection of this model because I’ll be compiling in the FPGA bitstream which will require around 60kb.

A nice extra is the inclusion of a USB PHY in this device. I’ll connect up the USB data lines just in case I decided to do something with them in future. In common with all F0 models, this one runs a core clock of 48MHz and can source that clock from an internal PLL fed by a built-in internal 8MHz oscillator.



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Most of the I/O is self explanatory. You’ll see the FPGA, PLL and LTC6957 control pins as well as the USB data lines and the SWD programming pins. I’m including a full 20 pin header that will connect directly to the ST-Link/v2 programming device.

A number of status LEDs are provided. The power LED is self-explanatory. The link LED will provide an indication of recent bluetooth activity. The lock LED will light when the PLL is locked. The xref LED will light when the external reference is selected as the active input and the active LED will light when the FPGA is actively counting.

Bluetooth connectivity is provided by the cheap and easy to use HC-06 module.


The HC-06 bluetooth board

The HC-06 pairs to an Android device without MCU intervention and, once a connection is established you can just treat it as a 9600/8/N/1 UART.

 

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Bill of Materials

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