Welcome to my PCB layout and design/development blog site!

The main purpose of the site is to document some of my personal projects and design concepts for projects in the works. My current project is a small embedded ARM based computing module called the PMX42.

I’ve been using Eagle for over 15+ years and all of the PCBs shown here were designed and built in Eagle PCB by Autodesk Corporation.

PMX42 – Accelerating Product Development Nucleus

The PMX42 is a design concept I came up with for a 1/8 DIN size computing module with a 128×64 amber OLED display.  It’s not really a “meter” in the classic sense, but an open architecture computing module nucleus that accepts custom I/O cards to meet a wide variety applications. In effect, the I/O cards and firmware define the application and it’s use. So, for now, we’ll dub this module as the “Accelerating Product Development Nucleus“!

The PMX42 has lots of horsepower under the hood and is powered by  a powerful Texas Instruments Tiva TM4C1294NCPDT ARM® Cortex™ M4F microprocessor. The Tiva processor operates at 120-MHz and achieves 150 DMIPS performance while providing 1024 KB Flash memory for code and 256 KB single-cycle system SRAM for dynamic memory use.

The onboard peripherals includes a 10/100 Ethernet MAC, USB 2.0 OTG, SD memory card slot and option slot for internal WiFi or Bluetooth card. The PMX42 also provides on-board power and regulation to provide 3.3V, 5V and +/-12V to each  I/O card slot on the motherboard.

Each slot contains I/O pins to the Tiva’s quad synchronous serial interface (QSSI) modules with advanced high speed quad SSI support. The first two slots are wired to one SSI controller and the second two slots are wired to a second SSI controller. Each slot has it’s own dedicated interrupt and slave select line wired to the processor GPIO’s. Additional multifunction GPIO’s are available on each slot as well. Slots 3 & 4 have dedicated high speed UART and serial lines to support a variety of communications options.


The entire PMX42 enclosure and boards were all 3D modeled and designed in Geomagic by 3D Systems. All of the sheet metal pieces in this design were laser cut and formed to tight tolerances (within 5 mil) by PCI Pro Coaters Inc right here in Atlanta Georgia. Give the guys at PCI a call if you need any professional sheet metal work done – they do amazing work and are the best folks around!!


One of the first cards I designed was a generic RS-232 and RS-422 high speed serial card. The RS-232 is supported by the MAX3223 and supports speeds up to 250kbps with CTS/RTS flow control. The full duplex RS-422 port is supported by the SN65HVD1473D part with data rates up to 20Mbps.


A Bluetooth I/O card is available also which uses an off the shelf module for ease of integration. The Bluetooth module communicates to processor via a high speed UART interface.


The small signal relay card provides two SPDT relays for low-level switching and signal control. It also features three opto-isolated inputs that can be used to trigger from external events by pulling the inputs low to ground.


A dual 3-wire RTD temperature measurement card using Analog Devices AD7793 ADC’s in the works also. The AD7793 is a 24-bit low power, low noise, complete analog front ends for high precision RTD temperature measurement applications.

PMX42 – Firmware & TI-RTOS

The PMX42 operates under Texas Instruments TI-RTOS product as the operating system for maximum flexibility and ease of software development and hardware integration. This allows integration of stable drivers and software for the Ethernet, USB, WiFi and other peripheral devices by Texas Instruments.

The latest v7.0 version of Code Composer Studio is available for FREE and includes the compiler, debugger, analyzer and all tools for the complete line of Texas Instruments processors. Code Composer Studio provides a complete suite of tools used to develop and debug embedded applications. Also, TI provides a huge code base of networking components and drivers for a variety of TI parts and devices.



The best place to reach me is via my bobstarr.net contracting website.  Email is the best way to reach me, but you can call and leave a message if you like. Unfortunately, we’ve been forced to send all calls to the answering machine due to the daily constant onslaught of robo/spam calls.  I do check my messages frequently and will return calls if you leave a message with your number. I’m generally check email all day during working hours and try to respond quickly. Thanks for visiting my site!