Sometimes I get asked what exactly it is I do as a Digital Engineer. The answer is: a lot. A large part of this job is designing digital sub-systems and interfaces for our amplifier projects.

On the more complex end, we have requirements for a "system" composed of multiple chassis, each of which work together and need to communicate with one another. The system as a whole has to communicate with the user via interface. This seems like a good example to illustrate what a typical digital platform might look like.

The main two digital boards that are responsible for a majority of the work are the Master Digital Board and the Control Board.

Master Digital Board:

• This board is the "brain" of the digital architecture, and usually resides in it's own chassis. There is only one Master Digital Board in a given system.
• Controls and monitors local peripheral circuits for functionality and fault detection.
• Controls and monitors "Control Boards" located in other chassis, using an internal communication bus (e.g. RS-485).
• Handles commands and queries from the user interface, oftentimes a serial (e.g. RS-232) or Ethernet interface.

Control Board:

• This board is responsible for control of sub-chassis; there is one Control board per chassis (usually between 4 to 12 chassis for a given system).
• This board is controlled by, and reports to, the Master Digital Board.
• Controls and monitors local peripheral circuits for functionality and fault detection.

In addition, there are several other small digital boards in each chassis that provide supporting behavior to these two.
The Master and Control boards always contain microcontrollers to handle their sophisticated tasks.

I design the digital circuitry, and write the firmware, for the entire digital architecture myself; from inception through testing to system integration.

The design elements include:

• PCB designs (schematic, BOMs)
• Firmware design (microcontroller)
• Logic design (CPLD/FPGA)
• Board interconnections
• Internal serial bus design (typically RS-485)
• User interface design (typically RS-232 or Ethernet)
• Diagnosic port design (serial, typically RS-232)
• Test fixturing for hardware testing
• Documenation (instructions, procedures, test data sheets, etc)

There is one additional design element. The customer describes the interface protocol in a design specification, but does not provide anything to simulate their control system. So I also need to create some kind of custom software that can "speak" to the amplifier, so that we can control and test it.

This is actually my favorite part of the job - programming an interface on a microcontroller in the system, and then programming a GUI that can drive that interface. It's so much fun designing both halves of the interface, and seeing them work together!

Below is a diagram illustrating how all of these concepts work together, as well as some other images.