Arduino has been traditionally dominated by Microchip-Atmel chips. The Uno uses a 8 bit AVR, and the newer boards have a 32 bit SAMD21 ARM core. Enters a new alternative, code name “blue pill”; and it’s fantastic!
What is the STM32 Blue Pill?
The STM32 “Blue Pill” is a development board based on the STM32F103C8T6 micro-controller from STMicroelectronics. It has the following characteristics:
- 72Mhz ARM 32-bit M3 CPU Core
- 64 kb of flash
- 20 kb of RAM
- Lots of peripherals (2 I2C, 3 USART, 2 SPI, 1 CAN and even a USB 2.0!)
- 3V3 logic
It is named “Blue Pill” as a cheeky reminder that there are alternatives to the official Arduino/Atmel-based boards out there. Not only that; the chip is incredibly cheap for this level of performance. The board can be bought off Aliexpress for less than $2! With that in mind; it is impossible to justify the $42 price tag an Arduino Zero (48 Mhz Cortex M0+) commands.
What do you get?
The board is extremely bare, with just enough components to make it run. You can power it through the micro-USB connector but this is not really recommended. When powered through USB a tiny SOT23-5 regulator steps down the 5V input to 3.3V. The RT9193-33 supposedly used is capable of delivering up to 300mA. In practice, the regulator is a cheap knock off and going over 100mA will be enough to fry it. This will in turn feed 5V on the 3V3 rail which will fry the whole board.
Because of this severe limitation, power the board directly from a 3V3 regulated power supply if you can. If not, don’t even try to power anything from the board; not even a tiny temperature sensor.
The board has Arduino support through the stm32duino project but the code you program will have to be uploaded through a SWD (Serial Wire Debug) programmer. In order to save up on cost, the blue pill comes completely devoid of any proper USB interfacing. A ST-LINK/V2 works well and Chinese copies can be bought for about US$2. It’s therefore not really an issue but something to keep in mind nonetheless.
In a vacuum, the Blue Pill development board is a pretty mediocre board. It’s rather shoddily built and doesn’t offer much else than the raw micro-controller. But at the same time, it’s hard complain because it’s incredibly cheap and gives you access to a breadboard friendly, 72 Mhz 32 bit processor board!
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