Turning an idea into a working prototype requires a place to work and tools that will get the job done. Mouser Electronics and Bob Martin, senior engineer and subject matter expert in rapid prototyping at Microchip Technology, provides a high-level overview of the resources you will need to build and test prototypes.
Corporate engineers or those who have hardware accelerator support will have access to equipment and hardware. Entrepreneurial engineers and makers must either build their own lab or find access to the equipment they need. Regardless of who you are, every engineer will need some basic tools to develop their hardware project.
Every engineer needs a lab of some kind. Many begin with a workbench in their basement or garage. A great place to start is one of a number of well-equipped fab labs and makerspaces available for use at a reasonable cost (Figure 1).
Many of these facilities are associated with university engineering programs, but there are often programs and arrangements available that give qualified people access even if they are not directly involved with the university. Martin, notes that these facilities often come with a built-in community of engineers and enthusiasts who like to share ideas.
“It’s amazing how much people at colleges love to talk about engineering projects,” he said.
Eventually, many engineers want to build out their own lab space. The basic ingredients of a good bench are plenty of workspace, good lighting, and a good bench power supply. In addition to these basics, you will need components and test equipment.
Parts and components
When you begin building early-stage prototypes, you will start collecting parts. You may use a generic evaluation board, and in scrounging for components, you will discover that certain parts are popular. In working out key aspects of a design, you might purchase breakout boards from vendors to quickly test concepts and do rapid prototyping in a process that’s like building with electronic Legos.
Eventually, you will need to take that early-stage prototype consisting of breakout boards, wires, sensors, and other components all plugged into a breadboard and start refining the design with actual parts and components. That’s when you see the real benefit of working in a lab with a large collection of parts.
“Those part collections are like tribal knowledge. They’re the canon of popular parts that lab managers collect because they trust those parts. With that knowledge comes the schematic symbols and footprints whatever CAD package you’re using,” Martin explains.
Hardware test equipment
Every well-equipped lab will need these basic pieces of test equipment:
- Digital multimeter (DMM) – used to measure voltage, current, and resistance. In selecting a DMM, consider resolution (more display digits typically indicate higher resolution), accuracy, auto-ranging, and true RMS capabilities.
- Oscilloscope – used for testing analog sections of a circuit, this is an essential tool for analysing waveforms, troubleshooting circuits, and evaluating signal quality. When choosing an oscilloscope, consider bandwidth, which specifies frequency ranges it can measure, sample rate, the number of channels it can measure, its ability to store waveforms and the record lengths it can store, triggering capabilities, and the types and configurations of probes that are compatible with the scope.
- USB logic analyzer — used to display and test digital signals.
“The USB logic analyzer is the real star of the show, especially if you’re working with microcontrollers,” Martin said.
Key features to consider include the number of channels it can track, how much continuous signal measurement it can store, and sample rate. Some logic analyzers have their own displays, and some are designed to plug into a computer and run with proprietary software.
In addition to test equipment, you will need electronic computer-aided design (ECAD) to create schematics and printed circuit boards (PCB) layouts.
ECAD and Electronic Design Automation (EDA), provide essential functionality for designing electrical circuits, creating schematics, creating printed circuit board (PCB) layouts, and generating all documentation needed to fabricate PCBs and build PCB assemblies. Although high-end ECAD solutions can be very expensive, there are good free and trial versions that provide sufficient functionality for many projects. Also, using trial versions is a great way to check them out before investing in a premium version.
ECAD applications use standard symbols for building schematics, and they offer comparable features commonly used in electronic design. However, there are certain things to look for when deciding on the right ECAD package. These include:
- Complete functionality
It used to be that schematics were created in one ECAD application and PCB layouts in a separate program. Now most ECAD applications provide integrated end-to-end design functionality that starts with schematics and carries through directly to the PCB layout portion of the program. This is an essential capability.
- Intuitive interface
One of the most important selection criteria is whether you are comfortable using the application.
“These applications all have different user paradigms in how they organise their interfaces. One of these user interfaces is going to click with you and be much more intuitive than others. That’s the one you want,” Martin explained.
Martin advises downloading trial versions and working with them to find one you like.
“All the good packages, free or not, have excellent video tutorials,” he said. “If it’s sparse on video tutorials, you probably want to look elsewhere.”
- Flat and hierarchical schematics.
Many projects work fine with flat schematics, but more complex designs benefit from hierarchical schematics that allow you to collapse sections of the diagram while still seeing all the connections that go into that section.
“If your design is only a few pages long, flat schematics work fine. At some point, hierarchical becomes more manageable.You might start with a flat schematic, and if your design is getting to six or seven pages, you probably want to start looking at hierarchical,” said Martin.
- Back annotation.
Back annotation allows you to make a change at the PCB layout stage which automatically updates netlists and the schematic. For example, you may discover during layout that routing would be a lot easier if you switched some pins around, which you can easily do. This changes the PCB netlist, but with back annotation, it will also change the schematic netlist.
Creating a schematic is just the beginning of the design process. Once you have a good schematic,
you will need to turn it into a PCB layout for fabrication.
Most ECAD packages have PCB layout functionality integrated into the application. Here are some key features you want to consider when evaluating ECAD packages:
- Seamless integration and design constraints.
Seamless integration is complete functional integration between schematic design and PCB layout. You should be able to work on either and have those results reflected in the other. Design constraints are design rules such as board dimensions, trace dimensions, hole sizes, number of layers, and other essential design features. Being able to specify these design constraints in detail is fundamental to creating a board layout that will work and that can be fabricated.
- Trace length matching.
This is a very important aspect of PCB layout, especially in designs that involve high-speed signals where uneven trace lengths can cause variations in how long it takes signals to move through the traces. PCB layout functionality should support trace length matching.
- Auto-routing — proceed with caution.
Many ECAD applications support auto-routing, and some work better than others. It’s important that the auto-routing be fully controllable by design constraints. Auto-routing is not a function you would use to layout an entire board. It should only be used in certain cases, for instance in highly repetitive non-critical sections of a layout.
“Most applications do trace length matching automatically, and that is more important than auto-routing,” said Martin.
This is a standard but essential function of the ECAD application. This includes maintaining and outputting all the documentation for fabrication and assembly, including bill of materials (BOMB), assembly plots for board layers, and drill tables. Part of the documentation includes Gerber or ODB++ output files, which are used by the PCB manufacturer to fabricate your boards.
In addition to creating schematics, PCB layouts, and documentation, there is one other important function provided by design software. That is circuit simulation.
A circuit simulator uses schematic and mathematical models to simulate analog circuit operation for analysis. Without building an operational prototype, you can use circuit simulation to look at signal propagation in a circuit, power levels, and thermal dissipation. This is useful in early design stages to verify a design and help in component selection.
Simulation functionality is increasingly becoming a feature of ECAD applications, either through linking to Simulation Program with Integrated Circuit Emphasis (SPICE) a widely used open-source circuit simulator, or as an integrated part of the ECAD application. It can be very helpful in designing analog circuits, but it is less useful for digital components such as those involving microcontrollers.
For designs involving radio transmission or wireless connectivity, radio frequency (RF) simulation is essential in antenna design and evaluating the circuit for regulatory compliance.
RF simulation is a very expensive, specialised service. That, and the cost of getting Federal Communications Commission (FCC), certification for a wireless design is one reason many engineers use pre-certified modules in their RF designs.
When you have designed, bolt, and tested your PCB assembly, you will need to put it into an enclosure. For that, you will need mechanical CAD.
Many mechanical CAD applications provide 3D modelling functions capable of creating enclosures and supporting 3D printing. From the electrical engineer’s perspective. A key mechanical CAD capability is being able to import a 3D step model of the PCB board that is generated by your ECAD application. This enables you to quickly see now the assembled board fits into the enclosure and where all the touchpoints will be.
“PCB board designers work with mechanical Packaging guys,” explained Martin. “They’ll generate that 3D STEP model and hand it off to the mechanical CAD guys who will pull it into the enclosure, rotate it, and take dimensions from it if necessary.”
Working with Digital Components
In addition to the ECAD tools and test equipment discussed so far, many designs require digital components such as microcontrollers and field-programmable gate arrays (FPGAs) that need their own development tools and strategies. Many development tools used to program these pals, such as the integrated development environment (IDE) for microcontrollers, will be specific to the part or part family you are using. In the case of FPGAs. you will likely be using a hardware description language such as Verilog or VHDL. In both cases, you will need logic simulators designed for digital circuits that allow you to incrementally step through code one instruction at a time and measure how each line of code affects signals in the circuit.
You will also use testing strategies, such as function partitioning, which allow you to isolate just one portion of the digital circuit to test its functions independent of what is happening in the rest of the circuit. This becomes necessary in complex circuits in which a microcontroller may be performing one kind of process while an FPGA is performing a different but dependent process.
Reprinted with permission from Mouser Electronics. https://au.mouser.com/