STM32 board a.k.a Blue Pill is a Development board for the ARM Cortex M3 Microcontroller. It looks very much similar to the Arduino Nano but it packs in quite a punch. The Development board is shown below.

These boards are extremely cheap compared to the official Arduino boards and also the hardware is open source. The microcontroller on top of it is the STM32F103C8T6 from STMicroelectronics. Apart from the Microcontroller, the board also holds two crystal oscillators, one is an 8MHz crystal, and the other is a 32 KHz crystal, which can be used to drive the internal RTC (Real Time Clock). Because of this, the MCU can operate in deep sleep modes making it ideal for battery operated applications.

Since the MCU works with 3.3V, the board also houses a 5V to 3.3V voltage regulator IC to power the MCU. Even though the MCU operates at 3.3V most of its GPIO pins are 5V tolerant. The pin of the MCU are neatly pulled out and labelled as header pins. There are also two on-board LEDs, one (red colour) is used for power indication, and the other (green colour) is connected to the GPIO pin PC13. It also has two header pins which can be used to toggle the MCU boot mode between programming mode and operating mode

specifications

• Architecture: 32-bit ARM Cortex M3
• Operating Voltage: 2.7V to 3.6V
• CPU Frequency: 72 MHz
• Number of GPIO pins: 37
• Number of PWM pins: 12
• Analog input Pins: 10 (12-bit)
• USART Peripherals: 3
• I2C Peripherals: 2
• SPI Peripherals: 2
• Can 2.0 Peripheral: 1
• Timers: 3(16-bit), 1 (PWM)
• Flash Memory: 64KB
• RAM: 20kB