Blue Pill

As a lot of other people, when I decided to check out the STM32, the first development board I ordered was a so-called Blue Pill board (so named because most of them are indeed using a PCB with a blue solder mask. These boards are readily available and they can be extremely cheap at around $1.50 (on AliExpress).

These Blue Pill boards generally follow the same recipe:

• (Claim to be) Based on a STM32F103 processor
• Same footprint (I/O pins)
• 8 MHz main crystal
• 32.768 kHz RTC crystal
• USB Micro-B connector
• Programming header

Fakes and Clones

Unfortunately, these boards often retail well below the cost of an actual STM32F103 processor (they are starting around $2), so most (if not all) of them are using various STM32F103 clones. ST themselves did not design the core in these processors. That was designed by and licensed from ARM. Other vendors can - and do - license the same core and build a processor which might not be exactly identical but almost and some of these are quite a lot cheaper than the original ST version.

A few of these board clearly use one of the clone processors and that is quite OK. Unfortunately, as is clear above, some also use clones which are LABELLED as something they are not.

In short - avoid these cheap clones as you would the plague and get something else - for example a Black Pill. They are not worth your time guessing.

There are a number of "clones" of the STM32F103 available. Most of those are likely properly licensed Cortex-M3 cores with peripherals designed to match the original STM32 and most can be used as drop-in replacements with some "quirks".

Unfortunately there are also quite a lot of fake chips available:

Confirmed fake STM32F103 (possibly a HK32) from some random Blue Pill	100 % real STM32F103 from my own Green Pill board

These are chips labelled STM32F103xxx but they are not. Notice the rough surface of the chip in the left image above, indicting the original label have been sanded off before a new one applied.

Pinout

The pinout of the Blue Pill boards is largely identical to the Black Pill boards and is shown in the following diagram.