Wednesday, May 14, 2014

STM32 Nucleo Boards

I have just received two nucleo boards: the L152RE and the F401RE. This is my first impression.

The Nucleo boards are the last entry level boards in the STM32 family.

STM32 Nucleo advertising
In the last years ST has provided the fantastic Discovery boards. Those boards, specially the STM32F3, STM32F4, STM32F401 and STM32F429 pack a lot of power for their price. Unfortunately they are not easy on the beginners. Of course there are projects like ChibiStudio or CoIDE that ease the programming of these boards but they are not as easy as Arduinos, for instance.

But that changes with the Nucleo boards. Those boards are mbed enabled. Mbed is a development platform for ARM microcontrollers. It started with the ARM Embed board based on NXP LPC microcontrollers. What is special about this platform is that it is web based. You don't need to install any toolchain in the computer and the source files are available everywhere. And, as in the Arduino case, you get libraries for all the board peripherals. Off course, a web based compiler is not the solution for everyone. For instance you cannot work offline.

mbed web compiler
You write the code from scratch or from one of the examples available. Hit the compile button and a binary file is generated that you can directly drop on the mbed board that shows on the PC as a mass storage drive. Quite easy.

The Nucleo F401RE Board

The nucleo boards are not the only mbed boards. They are only the last ones in the mbed world but are well positioned next to several cheap boards from Frescale that are mbed enabled too and range from the basic 32KB Flash FRDM-KL05Z to the 1MB Flash Ethernet enabled FRDM-K64F.
The original LPC mbed boards are not so well positioned in price or specs.

In this article I will talk about the F401RE Board that is the best specified nucleo board available. I don't have first hand experience on the Freescale mbed enabled boards buy they seem to be very interesting boards too.

Nucleo F401RE board
The Nucleo F401RE board includes an ARM Cortex M4 STM32F401RET6 microcontroller with 512KB of flash memory. As all nucleo boards are equally priced I see little point in buying any other nucleo board unless you have very special requirements.

In the above figure I have encircled the two clock crystal empty slots. Some figures show them populated but you must be aware that the they are not in the board. You will normally get the clock from the upper side of the board that includes the USB connector but if you separate both board pieces you will have no crystal clock for the board. And, of course, if you need a 32kHz clock for the real time clock you would need to solder it yourself.

The nucleo boards are compatible with the now "standard" Arduino headers.

F401RE Arduino headers
If, as in my case, you don't mind about Arduino compatibility you can use the dual row Morpho headers that include more signals that the Arduino headers and don't include the damm non 100 mil pitch space of the right arduino headers.

F401RE Morpho headers
This is a very capable board. The ARM Cortex M4 processor includes a FPU that speeds any 32bit floating point operation. As an example I have tested that the board can calculate 40000 times the square root of a float quotient in only 25ms. Its not as fast as a STM32F4 Discovery board but is a quite good spec for a board so cheap and easy to program.

All in all I'm quite pleased with this board. Packs a lot of power for its price and its very easy to program.
In the future I plan to try to program it using more traditional development tools under eclipse but for now mbed is working quite well. In fact I like this environment more that the Arduino one.

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