STM32 'Blue Pill' Breakout Board

**Port breakout board for the generic STM32 'Blue Pill' development boards**   *May also support Red/Black Pill boards where pinout/size is compatible with the Blue Pill board.* # Description: # This board breaks out the ports of the STM32 Blue Pill development board, and was designed as a more permanent but similarly flexible alternative to a breadboard solution. I plan to use this as part of a SCARA robot design as I needed a flexible MCU configuration that supports a modular approach (one that can adapt as the robot design evolves), whilst also working in a difficult environment (vibration etc.). # Status: # **Tested** - thr board has passed a basic continuity test and testing of the ports with a STM32 blue pill installed (uarts, gpio and i2c, not able to test spi). *Revisions identified incorporated in the the current PCB design* Revisions made: - inclusion of +5v jumper (J1b) to enable disconnection of +5v line to Blue Pill board (to enable USB power to be connected at same time). - rewired connections to PA8-12 & 15 GPIO pins (original board version inverted order). - PB0-PB15 silk screen labels rotated 180 degrees to the same orientation as PA & PC labels. # Features: # - Breakout ports - all available GPIO (Digital/ADC/PWM) pins, 3 x Serial, 2 x SPI and 2 x I2C ports plus an external NRST connection point (for a panel reset switch). - Ports offer +3.3v and GND as well as signal lines, where a port is +5V tolerant then a voltage selection jumper allows the selection of +5v or +3,3v. - GPIO pins are provided as GVS (ground, voltage, signal) configured headers. Both +3.3v and +5v (where a pin is +5V tolerant) GVS headers are available. - Supports an external power terminal block / soldered leads (rather than UNO style plug/socket setup on board) for +5v, GND and +3.3v. - MCU Blue Pill board can be powered from external +5v, external +3.3v or from its own USB port. - Power distribution pins (8x each rail: +5v, +3.3v and GND) - for powering external boards (low power only, not advised to use the +3.3v power distribution pins if using internal Blue Pill LDO +3.3v supply). - Battery connector for CR2032 style batter (uses vertical battery holder or can be wired to a separate battery pack) - for battery backup (RTC etc.) # Build Points: # Probably better to use SIL strips for headers/jumpers rather than the listed BOM components - e.g. use two 20 pin female strips for the STM32 MCU Blue Pill board (assuming MCU board has supplied pins soldered) to make the MCU board removable, and male pin strips for the ports, jumpers, power distribution and GPIO pins connections. The battery socket and power plug components are correct in the BOM. # Notes: # - The board has been manually routed rather than auto-routed (tool wasn't able to complete), and has additional grounding copper added through the use of via's *(probably overkill)*. - The STM32 MCU overloads multiple functions on the same pins, not all ports are available at the same time (please see ST documentation). - NRST offers GND connection only (has internal pull up on MCU), the signal pin can also be used to connect to RST pin on a STLink v2 programmer (original or dongle clone) to support allow SWD JTAG reset - GPIO pins are grouped in rows by port family, e.g. PA, PB and PC family pins grouped together (in numerical order). Each pin is configured as a column of GVS pins, signal pin centred and the +3.3v header connection pointing towards the centre of the board. Where a pin is +5v tolerant two further rows of pins offer an additional GND and +5V pin (point towards the edge of the board). This allows a signal pin to be configured in either +3.3v or +5v operation by simply plugging the cable either with the V line towards the center of the board (for +3.3v) or towards the edge of the board for +5v operation (i.e. rotating the plug/cable 180 degrees on the signal pin selects the desired voltage). - Flexible power supply options - can be powered via +5v and/or +3v.v external connector on the breakout board or via the Blue Pill's own USB port (potentially JTAG port as well, +3.3V only). This allows various power supply options for differing power supply/current demands. Also supports avoiding using the onboard Blue Pill's +3.3v LDO, which can fail on overload and over power the STM32 chip. - No onboard volatage regulators or protection on the breakout board to keep the board small, focussed on port expansion and the component count low. Care should be taken in connection power/port pins correctly. - The offboard PSU needs supply sufficient current to power the breakout board and any external boards connected. - High power demand boards (e.g. amps, motor drivers etc.) boards connected should be powered directly from a PSU/own regulator rather than via the breakout board power distribution pins. The breakout board is unlikely to supply sufficient current needed, and may also be impacted by electrical noise from the connected board. # Power Configurations # - J1a +3.3v Int/Ext Voltage Select - selects whether +3.3v to ports/gpio/power distribution is either powered from the external +3.3v supply or the Blue Pill's onboard LDO (not recommended). Not fitting the jumper isolates +3.3v from the port/gpio/power pins. - J1b MCU +5v selects whether the Blue Pill board is supplied +5v from the external power supply - useful if connecting the USB port to the Blue Pill board in order isolate the external +5v power supply from the USB power supply or 3.3v from JTAG. Also if powering Blue Pill from external +3.3v, allows isolation from +5v so the Blue Pill LDO is not used.  - +3.3V supply can be switched between an external +3.3V supply or an internal +3.3v from Blue Pill board (current limited, may damage the STM32 if too much current is drawn from the BLue Pill LDO). If using +3.3v power distribution outputs or multiple and/or power greedy devices from ports then an external +3.3v power source is recommended. - When using USB power and external +5v at the same time leave J1b open - disconnects the MCU 5V line (USB supplied) from the external 5v (external 5V supply used to power ports/GPIO only). Alternatively fit a Schottky Diode instead of the J1b header to allow both PSU to be used. - When using the USB power or external +5v, to power the Blue Pill MCU, and an external 3.3v supply at the same time then do not connect the Blue Pill 3.3V line to the external 3.3v supply (J1a must be set to *Ext*). - When using the external +3.3v **only** to power Blue Pill Board (i.e. all three pins on J1a connected) then J1b should be open - disconnects the +5v breakout board rail from the Blue Pill board to prevent any reverse current pull through the Blue Pill LDO if a +5v port/gpio is connected.