MSP430 Development with Linux
Flashing LEDs get boring pretty quickly. Once you get the bugs worked out of your blinking LED, you probably are going to want to design a custom PC board with interfaces to the outside world. One of my projects is a one-wire lock controller with an RS232 interface that uses Dallas Semiconductor iButtons for access control.
For this project, I chose one of the smallest of the family, the MSP430F1101 with 1KB of Flash and 128 bytes of RAM. It uses a pair of transistors to switch a DC motor on and off and a MAX3221 for serial communications with a PC. The C code to control the lock just barely fits into the 1K Flash space of the '1101. A low dropout voltage regulator is used to power the board and provide a clean reset to the processor. I drew the schematic and designed the board using Eagle CAD Lite under Linux. Eagle has several versions of its schematic and PCB auto-router, including a free version for noncommercial use:
Free for noncommercial use.
Board size limited to 3.2"x4" and two layers.
One schematic sheet.
Lite version for $49 US with same limitations as the free version.
Standard version for $600 US.
Pro versions for $1,200 US.
Linux, Windows and Mac versions are available
Eagle CAD is easy to get started with, low cost and very powerful. A user scripting language allows you to add features and customize the program to fit your needs. User support for Eagle is very strong, and the Web site has an extensive collection of user-created libraries.
The Eagle auto-router supports advanced features like back-annotation, keepout areas, design rules checks and one of my favorites—flood fill with thermal relief. If you have ever tried to solder a pin surrounded by a large ground plane, you will appreciate the advantage of thermal relief on power pins. Without it the ground plane acts like a large heat-sink and solder won't stick. All levels of the PCB and Schematic editor support the concept of back (and forward) annotation. You can make changes on the PCB, and they will be reflected on the schematic and updates made to the schematic are reflected on the PCB.
After designing a PC board, you actually need to make one. You can etch your own, but it is difficult to match the quality of even the least-expensive board manufacturers. Some manufacturers will accept Eagle PCB files directly, which saves you the step of converting the design to the Gerber format. The Gerber format is a lot like an old pen plotter, it tells PCB etching equipment where to draw the trace and how large a line to draw. Most PCB manufacturers still require Gerber files, so Eagle includes a script to output the necessary Gerber files.
One difficulty in dealing with Gerber files is that although Eagle can export the PCB in the correct format, it has no way to view the output to verify it was converted correctly. Linux has needed a good Gerber viewer for years, but it has been available only with recent releases of the gerbv program. It isn't as intuitive as I would like, but it does function well enough to display the Gerber files so that you can check the final output before sending it off to have 1000 of your latest widget design created.
I have used four different PCB manufacturers myself. Their prices and features vary, but customer service and quality from all four have been excellent. Olimex and PCB Pool both accept Eagle CAD files directly, with no need for conversion to Gerber. Olimex is in Bulgaria, and turn-around time can be up to three weeks, but prices are excellent. PCB Pool is in Ireland and has quick turn-around or longer turn-around times, depending on price (as do most). I used PCB Pool for the one-wire Wi-Fi boards (Figure 6).
AP Circuits is in Canada and has very good prices and very fast turn-around. The bare one-wire lock boards were ordered on a Saturday, and I received them on Wednesday. I ordered them with no silkscreen or solder mask in order to keep the price low. For production, I used E-Teknet for my DT-1A temperature sensor boards with excellent results.
The MSP430 is a fun and easy-to-use processor; its wide range of features and access to free development tools and low-cost JTAG hardware make this processor a good choice for both the hobbyist and the professional developer. Using the GNU gcc toolchain reduces the learning curve and allows you to use the same tools for developing code on the MSP430 that you would use for Linux projects. My set of development tools includes make, gcc, gdb and joe.
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Brian C. Lane lives in Port Orchard, Washington, with his wife and son, who is a huge Tux Racer fan. He serves as Webmaster For Life for the Kitsap Peninsula Linux User Group and writes Linux apps in his spare time.
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