Implementing Design Ideas Gets Easier


A few years ago, I tried to push for a standard low- to medium-speed connector and board layout for small peripherals because the typical expansion board standards like PC/104 were pushing rather large boards. This type of connector also could find a home with prototype boards, which had been sporting any number of proprietary, one-off interfaces designed specifically to highlight the device or microcontroller they were hosting.

Standard interfaces likes Mini PCI Express (PCIe) and SUMIT have nice compact form factors, but they have many problems in the low-end space (see “SUMIT Brings Big Improvements In Small Packages” at First, PCIe is not available with most microcontrollers. PCIe board layout is also a challenge. Finally, the connector is expensive compared to simple pin headers.

Platforms like Stackable USB utilize interfaces that are more common with microcontrollers, and they have smaller board form factors (see “USB Thinks Inside The Box” at The problem is that they have not achieved wider adoption outside of some embedded applications.

Platforms Dominate

What has happened is the rise of open-source hardware platforms including Arduino, Raspberry Pi, and BeagleBone (Fig. 1), to mention just a few of the more popular platforms (see “Arduino, Raspberry Pi, Or BeagleBone?” at There are more out there, but these three tend to dominate the prototype/hobbyist market because of their low cost, simplicity, and extensive support.

It would have been nice if the various platforms had been built using a common expansion interface, but they were more likely put together in an ad hoc fashion. Like many prototype kits, they were based on the available I/O. No more and no less.

The popularity of these platforms has led to some interesting combinations, though. Take Microchip’s new chipKIT Pi (Fig. 2). This Arduino form-factor board includes a 32-bit MIPS-based PIC32 microcontroller that also has a Raspberry Pi expansion socket.

Blending the Arduino and Raspberry Pi is not as easy as just dropping a few sockets onto the board. The Raspberry Pi uses a 3.3-V microcontroller. The Arduino is specified as a 5-V part so the peripheral cards need to be designed for their intended hosts.

The Arduino and Raspberry Pi form factors have generated a lot of peripheral board designs, from cameras to LCDs. They provide a way to prototype quickly and to gain access to new peripheral chips like 10-DOF (degrees of freedom) microelectromechanical systems (MEMS) sensors delivered on matching peripheral boards.

Microchip isn’t the only vendor with boards that follow these popular form factors. Freescale’s Freedom line supports Arduino expansion boards. The Freedom FRDM-KE02Z boards run a 20-MHz Arm Cortex-M0+ microcontroller.

These platforms were not designed for production use, but they can be suitable for building mock-ups of a final product. A low-profile connector and better mounting support would be required. Likewise, most final designs would be based on a custom board that would be much smaller than the prototype. Designing that board would be much easier since most of these platforms are open-source designs.

I would have preferred a standard that vendors could support with more rugged boards, but it is hard to argue with success. These platforms have garnered a wide audience and have become important for education as well.

By the way, the chipKIT Pi is only $28, and the microcontroller is in a DIP socket. 

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William Wong

Bill Wong covers Digital, Embedded, Systems and Software topics at Electronic Design. He writes a number of columns, including Lab Bench and alt.embedded, plus Bill's Workbench hands-on column....
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