Monday, February 18, 2013

Four STM32-Discovery BaseBoards

BusBoard has developed three baseboards for the Discovery-F4, Discovery-F3, and Discovery-VL modules.  These were originally developed for use in Kornak Technologies projects.  The baseboards are now available for purchase as bare PCBs.

Discovery-F4 BaseBoard

Click to Enlarge
STM32-F4B1 BaseBoard Features [Click to Enlarge]
The baseboards  are designed to maximize the number of UART ports and peripherals that can be added to the Discovery boards.  The STM32-F4B1 baseboard is a 4-layer PCB that measures 160x160mm. 
Three serial interfaces can be added using ComBoard modules.  ComBoard is an open standard developed by BPS for adding UART peripherals to development boards.  ComBoards have 10 pins for all RS232 handshaking signals plus power, although many modules will just use Tx/Rx and possibly RTS/CTS. 
ComBoards were first used on the AVR-1284 board.  The most obvious UART use is for RS232 or RS485 interfaces.  USB ComBoards are helpful when using newer PCs without DB9 serial ports.  Other UART driven peripherals also lend themselve to ComBoard modules, such as GPS and WiFi modules.

For other peripheral types, the baseboard can accept two APSICE interface boards.  ASPICE is a 14-pin module standard.  ASPICE stands for Analog+SPI+I2C, and the expansion boards can use one or more of these interfaces.  The first two ASPICE boards created are the AS-RTC1, a STMicro M41T93 super-accurate RTC module (SPI interface) and the AS-TEMP1, a digital thermometer (I2C interface).

I will be writing articles about ComBoard and ASPICE in the near future.  For now the pinouts can be seen on the baseboard schematics (see links below).

A SD-Card with SPI interface is provided with a FET to control power to the card.  A 20-pin JTAG header is available allowing an external JTAG programmer to be used.  JTAGs are faster than the SWD (serial) programmer provided on the Discovery module which helps to speed up bigger projects.

Every 16 bit GPIO port is brought out to two 16-pin headers.  Each header has 8 data bits and +5V, +3V3 power and ground.  They make it easy to connect to solderless breadboards with jumper wires or with DIP16 cables.  The GPIO headers are designed so that all 16 GPIO pins can be brought out to a single header if needed by soldering in some wire jumpers.

If you are designing with the STM32-F4, you may find a spereadsheet I have created useful for planning which pins to use for your project.  "Pinout Spreadsheet for the STM32F4-Discovery"

Datasheets and photos are on the BusBoard web site for PCB-STM32-F4B1.

The STM32-F4B1 schematics and BOM can be found at

Discovery-F3 BaseBoard

The STM32-F3U baseboard for the Discovery-F3 is smaller at 100x160mm.  This standard 3U format fits some off-the-shelf 3U sized enclosures [pdf].  It uses a 4-layer PCB to bring out all of the Discovery-F3 signals.
STM32-F3U BaseBoard Features [Click to Enlarge]

Like the F4 baseboard, each GPIO port is brought out to separate headers.  However, to save space, expansion is achieved by using four UEXT style headers.  UEXT provide UART, I2C, and SPI signals on a 10-pin header and it uses 10-pin ribbon cables to connect to peripheral boards.  UEXT is and open standard developed by Olimex, and many UEXT peripheral modules are available.  The down side to UEXT is that only RX/TX are available for the UART.

On the STM32-F3U, each of the four UEXT connectors uses a different USART.  Two different I2C ports are available.  The SPI strobes can be disconnected at jumpers and connected to different signals if needed for flexibility.

If you are not sure whether to use a ST-Micro Discovery-F3 or Discovery-F4, I have written two summaries, one comparing the microcontrollers and another on comparing the Discovery boards.
"STM32 Discovery-F3 and Discovery-F4 Differences"
"Introducing the STMicro F3 Family of ARM Cortex-M4 Microcontrollers"

Datasheets and photos are on the BusBoard web site for PCB-STM32-F3U.

The STM32-F3U schematics and BOM can be found at

Discovery-VL BaseBoard

 The STM32-VLB1 baseboard is designed for STMicro's first ARM module, the Discovery-VL.   It is a 2-layer 160x160mm PCB.  Three ComBoard modules and six ASPICE modules can be populated.  It also has a SD-Card and a JTAG interface similar to the F4 board.
STM32-VLB1 BaseBoard Features [Click to Enlarge]

If you don't need the memory or features of the F4, I recommend the Discovery-VL module.  It has a nice STM32F100 MCu and it costs less than the other modules.  It has SIL headers that allow it to be directly plugged in to solderless breadboards.

Datasheets and photos are on the BusBoard web site for PCB-STM32-VLB1.

The STM32-VLB1 schematics and BOM can be found at

Bare BaseBoard PCBs Available

I have baseboard PCBs available if you would like to build your own.  The prices for them are below.  The STM32-F3U board includes a bare UEXT board to build a serial interface.  I am also including two 50-pin DIL sockets with F3 and F4 boards because the sockets can be expensive to buy in low quantity.  The VLB1 board has the necessary SIL sockets (two 28-pin and one 6-pin).

PCB-STM32-F4B1    $28 USD (bare PCB and two 50-pin sockets)
PCB-STM32-F3U     $22 USD (bare PCB and two 50-pin sockets)
PCB-STM32-VLB1   $18 USB (bare PCB three SIL sockets, two 28-pin and one 6-pin)

Please send me an email to if you have any suggestions or comments, or would like to arrange a purchase.  Shipping is not included.

Another F4 BaseBoard, with Ethernet

The STM32-F4B1 baseboard is designed for flexibility to attach multiple UART, SPI, I2C, GPIO and analog driven peripherals.  However, it doesn't take advantage of the Discovery-F4 board's Ethernet interface.  Some of the the Ethernet pins are used for other interfaces.

If you need Ethernet, EmBest/Element14 have a new Discovery-F4 baseboard which has Ethernet, one UART, a micro-SD card, and an expansion header.  It is called the STM32F4DIS-BB extension board and it sells for $35.  A color LCD and a camera board are also available for it.
STMicro's page for the STM32F4DIS-BB

EmBest Manufacturer's page for the STM32F4DIS-BB

The three Embest boards can be bought from Element14/Newark at this link.
Element14 community page for the STM32F4DIS-BB.

Why are Breakout BaseBoards Needed for Discovery-F3 and F4?

1. The Discovery-VL, L, and F0 modules use single row headers which can plug into a solderless breadboard for prototyping.

The Discovery-F4 and Discovery-F3 use dual row headers which prevent a solderless breadboard from being used because adjacent pins will be short circuited. A baseboard provides breakout connectors to allow the easier connections to the port signals. It simplifies prototype assembly if you need to connect to a lot of pins.

There are other ways to connect to a lot of  Discovery-F4 pins, but they take more work than a ready made baseboard. See the blog page “A Breakout Board for the STM32F4-Discovery” for one example.
It shows a way to break out the Discovery-F4 connectors using zig-zag pattern BusBoard, but it requires some track cutting and soldering.  Kits are available that include two BusBoard proto boards and the two required 2x25 pin sockets, KIT-BB2-F3+F4 (size 2) or KIT-BB3-F3+F4 (size 3).

2. Engineers and technicians often want a quick way to get a prototype running to start firmware development while waiting for the hardware team to complete the application hardware.

A Discovery board with a few serial port and peripheral modules provides enough functionality to allow firmware development to begin.  I have used Discovery boards for several projects in this manner.

Sometimes Discovery boards are better than the more expensive ST Micro Eval boards for prototyping because they have more uncommitted ports and pins. This is due to fewer on-board peripheral chips.  Sometimes eval board pins are connected to ICs that can’t be easily disconnected (and I hate damaging a nice eval board to remove functionality).

Please send me an email at if you have any questions, suggestions, or comments.